Rapid activation method and system of PEM fuel cell stack

Abstract

The invention relates to the technical field of fuel cells, and provides a PEM fuel cell stack rapid activation method and system, and the method comprises the following steps: S1, connecting a to-be-activated fuel cell stack to a load, introducing air into a cathode of a fuel cell, introducing hydrogen into an anode of the fuel cell, and loading to a rated current or a rated voltage of the fuel cell for self-humidification; s2, changing the load to a first single-chip voltage, and recording a first current corresponding to the first single-chip voltage; s3, greatly reducing the air supply of the cathode of the fuel cell, and adjusting the load to adjust the current to a second current after the voltage of the single sheet is reduced to be lower than the second voltage of the single sheet, so that the membrane electrode of the fuel cell is subjected to hydrogen pump reaction; s4, recovering the air supply amount of the cathode of the fuel cell, recovering the current to the first current, and recording a third monolithic voltage; s5, repeating the steps S3 and S4 until the voltage of the third single chip is stable; and S6, loading the rated current or the rated voltage of the fuel cell to carry out self-humidification. The method has the advantages of accelerating activation of the fuel cell stack and reducing the hydrogen consumption.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and more specifically, to a rapid activation method and system for a PEM fuel cell stack. Background Art

[0002] After the proton exchange membrane (PEM) fuel cell is manufactured and assembled, due to its low initial performance, it needs to undergo a process called break-in to maximize the performance of the fuel cell. The main body of the activation is the membrane electrode (MEA) called the power generation unit, and its structure is mainly composed of the anode and cathode gas diffusion layers (GDL), catalyst coating (CL) and proton exchange membrane (PEM). Fuel cells that have not been activated have low activity due to impurities and oxidation on the surface of their catalysts, large contact resistance between components after assembly, impurities affecting electronic conduction, proton exchange membranes not being humidified and impurities affecting proton transfer speed, and the mass transfer channels of the three-phase interface and water vapor not being optimized. These adverse factors will affect the performance of the fuel cell.

[0003] With the advancement of fuel cell industrialization, traditional forced current or forced voltage activation often takes several hours or even dozens of hours to activate. Traditional activation methods not only require a lot of time cost, but also consume a lot of fuel (hydrogen) for a long time with high current activation. With the advancement of fuel cell technology, the power requirements for fuel cells are also constantly increasing. Many existing activation methods can often only optimize one or two of the activation loss, ohmic loss, and mass transfer loss of fuel cells.

[0004] In patent CN106450381A, the patented method supplies oxygen and hydrogen to the fuel cell stack and then cuts off the supply of oxygen and hydrogen; then short-circuits the adjacent cells of the stack electrically; after the voltage drops to 0V, oxygen and hydrogen are supplied to the stack again and a predetermined current is applied; then the voltage is reduced to 0V by short-circuiting the electrical connection to remove the oxygen remaining in the stack; after a short break, oxygen and hydrogen are supplied to the stack again; after the above steps are repeated several times, activation is completed. This method requires an additional electrical short-circuit device between the cells, and the current is huge and uncontrollable when the cells are short-circuited. This method cuts off the supply of oxygen and hydrogen at the same time when the short circuit occurs. Cutting off the hydrogen supply has the risk of local lack of hydrogen causing reverse polarity damage to the fuel cell membrane electrode.

[0005] Therefore, it is of great practical significance to study an activation method that is fast, efficient and can stably improve the performance of fuel cells. Summary of the invention

[0006] The present invention aims to overcome at least one defect (shortcoming) of the above-mentioned prior art and provide a method and system for rapidly activating a PEM fuel cell stack to efficiently activate the fuel cell.

[0007] An object of the present invention is to provide a method for rapid activation of a PEM fuel cell stack, comprising the following steps:

[0008] S1. Connect the fuel cell to be activated to a load, introduce air into the cathode of the fuel cell, introduce hydrogen into the anode, and load the rated current or rated voltage of the fuel cell for self-humidification;

[0009] S2, changing the load to the first single-chip voltage, and recording the corresponding first current;

[0010] S3, greatly reducing the air supply to the cathode of the fuel cell, and when the single-chip voltage drops below the second single-chip voltage, adjusting the load to adjust the current to the second current, so that the fuel cell membrane electrode performs a hydrogen pump reaction;

[0011] S4, restore the air supply to the cathode of the fuel cell to restore the current to the first current, and record the third single-chip voltage;

[0012] S5, repeating steps S3 and S4 until the voltage of the third single chip is stable;

[0013] S6. Load the rated current or rated voltage to the fuel cell for self-humidification to complete activation.

[0014] In step S1, the membrane electrode is the core component of the fuel cell stack. Since the newly produced membrane electrode is not humidified and due to the hydrophobic characteristics of the gas diffusion layer, it is still difficult to enter the catalyst layer and the proton exchange membrane by simply relying on gas humidification to carry water. This solution uses the self-produced water characteristics of the membrane electrode itself at high current to perform self-humidification before the hydrogen pump is activated, which greatly shortens the activation time of the hydrogen pump; preferably, in step S1, the humidity of the air and hydrogen is 80%-150%; the self-humidification time is 5 to 10 minutes; the anode and cathode back pressures and stoichiometric ratios are the back pressures and stoichiometric ratios designed for the stack; the stack cooling water temperature is in the range of 60-80°C for normal stack operation.

[0015] In step S2, preferably, the first monolithic voltage is 0.7-0.8V, and the first monolithic voltage is maintained for 10-60s. The anode hydrogen flow mode is set to a stoichiometric ratio mode, and the stoichiometric ratio used is the designed stoichiometric ratio of the stack. The cathode air mode is set to a fixed flow mode, and the fixed flow used is the designed flow of the stack corresponding to the first current. Since the catalyst in the membrane electrode catalyst layer is usually platinum, and an excessively high monolithic voltage will accelerate the dissolution of platinum, an appropriate first monolithic voltage setting can prevent the dissolution of the platinum catalyst, thereby extending the service life of the fuel cell.

[0016] In step S3, the air supply is greatly reduced, which means reducing the air supply by more than 90%. The fuel cell quickly consumes the oxygen at the cathode, the catalyst active sites can be activated to the maximum extent, and the single-chip voltage drops rapidly to below the second single-chip voltage. At this time, a "hydrogen pump reaction" is formed, and the protons generated at the anode are converted into hydronium ions (H3O + ) is conducted through the proton exchange membrane in the form of hydrogen and then reduced to hydrogen in the absence of oxygen at the cathode. This not only wets the membrane electrode, but also this part of hydrogen can further reduce and remove oxides and other impurities on the surface of the cathode catalyst. The hydrogen pump reaction of this scheme does not require an external power supply. At the same time, the nitrogen remaining after the oxygen in the air is consumed can be used as a protective gas, and there is no need to provide additional nitrogen protective gas. This simplifies the operation steps and reduces costs. Preferably, the second single-chip voltage is 0.01V~0.1V, and the second current is 1~50A. More preferably, the second single-chip voltage is 0.05V~0.1V, and the second current is 5~15A.

[0017] In addition, if the air supply is directly cut off, due to the natural back pressure, the remaining air in the pipeline can only be discharged along the battery flow channel after the air is cut off, and the diffusion is slow, which will greatly increase the voltage drop time. There are differences in the flow resistance of each membrane electrode in the battery stack, and the speed of consuming the remaining air is different. The inconsistent voltage drop speed of the single membrane electrode will cause differences in the activation effect, and even the voltage drop speed of individual membrane electrodes is too fast, which can easily lead to negative voltage reversal. Although the air supply in this solution is greatly reduced, it is still in a continuous supply state. The air is flowing in the cathode cavity, and the voltage of the single membrane electrode can drop rapidly with good uniformity. By discharging a large amount of excess air, the remaining gas in each membrane electrode is small and relatively consistent, which is conducive to maintaining the consistency of the voltage of the single membrane electrode and avoiding differences in the activation effect. In this way, the fuel cell can be effectively activated in a shorter time and the activation efficiency is improved.

[0018] Preferably, the hydrogen pump reaction time is 3 to 10 seconds. Since the hydrogen pump does not produce water and is a heat reaction, it should not be continued for too long to avoid affecting the activation effect and battery performance.

[0019] In step S4, the air supply is restored to the amount before the reduction, and the fuel cell produces water for self-humidification. As the activation proceeds, the performance of the fuel cell continues to rise. After the air supply is restored, the single-chip voltage will change at the first current. Preferably, in step S5, after repeating steps S3 and S4, when the third single-chip voltage does not change for three times, it means that the activation of steps S3 and S4 has been basically stable, and step S6 can be entered. In one or more embodiments of the present invention, in step S5, the number of times steps S3 and S4 are repeated is 30 to 150 times.

[0020] Preferably, in step S3, substantially reducing the air supply to the cathode of the fuel cell comprises: substantially reducing the air supply to the cathode of the fuel cell by controlling a bypass channel. In step S4, restoring the air supply to the cathode of the fuel cell comprises: restoring the air supply to the cathode of the fuel cell by controlling a bypass channel. In one or more embodiments of the present invention, the increase and decrease of the air supply is controlled by the on-off control of the bypass channel. Specifically, a bypass is connected to the air supply channel and a bypass valve is provided. When the bypass valve is opened, most of the air flows to the bypass channel, and a small part flows into the cathode chamber. When the bypass valve is closed, all the air flows into the cathode chamber, thereby restoring the original air supply. The amount of cathode air supply can be adjusted and controlled by the degree of switching of the bypass valve.

[0021] In step S6, forced high current self-humidification activation is performed again, preferably, the self-humidification time is 10 to 20 minutes. With the operation of the peak current, the contact interface and the electronic path structure between the components can be optimized to the maximum extent, reducing the ohmic loss; at the same time, when the peak current is running, the drainage channel and the gas transmission channel can be optimized to the maximum extent, achieving the purpose of optimizing the mass transfer loss.

[0022] Another object of the present invention is to provide a PEM fuel cell system, based on which any of the above-mentioned rapid activation methods is implemented, the PEM fuel cell system comprises: the PEM fuel cell system comprises a fuel cell stack, an air supply branch and a hydrogen supply branch, the air supply branch is used to provide air for the fuel cell stack system, and the hydrogen supply branch is used to provide hydrogen for the fuel cell stack system;

[0023] The air supply branch includes an air compressor, which is connected to the air inlet of the fuel cell stack through an air intake channel, and the air outlet of the fuel cell stack is connected to an air outlet channel. A cathode bypass channel is connected between the air intake channel and the air outlet channel, and a cathode bypass valve is provided on the cathode bypass channel.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The activation method of the present invention can greatly shorten the activation time of the fuel cell stack and save a large amount of hydrogen, thereby achieving rapid activation and saving costs.

[0026] (2) The activation method of the present invention has high consistency in the activation of the single-piece membrane electrode of the fuel cell, and can efficiently activate the fuel cell to give full play to the optimal performance of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural diagram of the PEM fuel cell system of Example 1.

[0028] Figure 2 This is a flow chart of the rapid activation method of Example 2.

[0029] Figure 3 This is the voltage diagram of the fuel cell stack activation process of Example 2.

[0030] Figure 4 This is the voltage diagram of the fuel cell stack activation process of Example 3.

[0031] Figure 5 This is a consistency diagram of the membrane electrode voltage drop of Example 2 and Comparative Example 2.

[0032] Figure 6 This is the voltage diagram of the activation method of Comparative Example 1.

[0033] Figure 7 It is a performance test diagram of the fuel cell stack after activation of Example 2, Example 3 and Comparative Example 1.

[0034] Figure numerals: fuel cell stack 100, air compressor 200, air intake channel 210, air intake valve 211, air outlet channel 220, air outlet valve 221, cathode bypass channel 230, cathode bypass valve 231, tail exhaust tank 240, hydrogen cylinder 300, hydrogen intake channel 310, hydrogen intake valve 311, gas-water separator 400, hydrogen outlet channel 410, tail exhaust channel 420, drain valve 421, circulation channel 500, hydrogen circulation pump 510. DETAILED DESCRIPTION

[0035] The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0036] Example 1

[0037] like Figure 1 As shown, this embodiment provides a PEM fuel cell system for activation, wherein the PEM fuel cell system includes a fuel cell stack 100, an air supply branch and a hydrogen supply branch, wherein the air supply branch is used to provide air to the fuel cell stack 100 system, and the hydrogen supply branch is used to provide hydrogen to the fuel cell stack 100 system.

[0038] The air supply branch includes an air compressor 200. The air compressor 200 is connected to the air inlet of the fuel cell stack 100 through an air intake channel 210, and the air outlet of the fuel cell stack 100 is connected to an air outlet channel 220. The air intake channel 210 and the air outlet channel 220 are respectively provided with an air intake valve 211 and an air outlet valve 221. The air intake channel 210 and the air outlet channel 220 are connected to a cathode bypass channel 230, and the cathode bypass channel 230 is provided with a cathode bypass valve 231. The air outlet channel 220 is connected to a tail exhaust tank 240.

[0039] The hydrogen supply branch includes a hydrogen bottle 300 and a gas-water separator 400. The hydrogen bottle 300 is connected to the hydrogen inlet of the fuel cell stack 100 through a hydrogen inlet channel 310, and a hydrogen inlet valve 311 is provided on the hydrogen inlet channel 310. The gas-water separator 400 is connected to the hydrogen outlet of the fuel cell stack 100 through a hydrogen outlet channel 410. The gas-water separator 400 is connected to the hydrogen inlet channel 310 through a circulation channel 500, and a hydrogen circulation pump 510 is provided on the circulation channel 500. The gas-water separator 400 is connected to the air outlet channel 220 through a tail discharge channel 420, and a drain valve 421 is provided on the tail discharge channel 420.

[0040] Example 2

[0041] like Figure 2 As shown, this embodiment provides a method for rapid activation of a PEM fuel cell stack, and the rapid activation method is based on the PEM fuel cell system provided in Example 1, comprising the following steps:

[0042] S1. Connect the fuel cell to be activated to the load, introduce air to the cathode of the fuel cell with an air humidity of 80%, introduce hydrogen to the anode with a hydrogen humidity of 80%, load to 565A (specific rated current or rated voltage), and perform self-humidification for 6 minutes;

[0043] S2, change the load to 0.7V for 10s, and record the corresponding first current as 295A.

[0044] S3, open the bypass valve, wait until the single-chip voltage drops below 0.1V, adjust the load to adjust the current to 10A, so that the fuel cell membrane electrode performs a hydrogen pump reaction, and the hydrogen pump reaction time is 3s;

[0045] S4, close the bypass valve to restore the current to the first current of 295A, and record the voltage of the third single chip as 0.71V;

[0046] S5, repeating steps S3 and S4 until the voltage of the third single chip does not change for three consecutive times, and repeating for about 130 times in total, and the voltage of the third single chip is stabilized at 0.752V;

[0047] S6. Load to 565A for self-humidification for 18 minutes to complete activation.

[0048] Example 3

[0049] This embodiment provides a method for rapid activation of a PEM fuel cell stack. The method is based on the PEM fuel cell system provided in Embodiment 1 and includes the following steps:

[0050] S1. Connect the fuel cell to be activated to the load, introduce air to the cathode of the fuel cell with an air humidity of 150%, introduce hydrogen to the anode with a hydrogen humidity of 150%, load to 565A, and perform self-humidification for 10 minutes;

[0051] S2, change the load to 0.76V for 20s, and record the corresponding first current as 215A.

[0052] S3, open the bypass valve, wait until the single-chip voltage drops below 0.05V, adjust the load to adjust the current to 15A, so that the fuel cell membrane electrode performs a hydrogen pump reaction, and the hydrogen pump reaction time is 10s;

[0053] S4, close the bypass valve to restore the current to the first current of 215A, and record the voltage of the third single chip as 0.766V;

[0054] S5, repeating steps S3 and S4 until the voltage of the third single chip does not change for three consecutive times, and repeating for about 80 times in total, and the voltage of the third single chip is stabilized at 0.785V;

[0055] S6. Load to 565A for self-humidification for 12 minutes to complete activation.

[0056] Comparative Example 1

[0057] In this comparative example, the fuel cell stack is subjected to conventional constant current activation, and the method steps are as follows:

[0058] S1. Connect the fuel cell to be activated to the load, introduce air to the cathode of the fuel cell with an air humidity of 100%, introduce hydrogen to the anode with a hydrogen humidity of 100%, gradually load to 565A, and operate at a constant current;

[0059] S2. Record the battery voltage. If the voltage does not rise within 5 minutes, reduce the load and stop the battery to complete activation.

[0060] Comparative Example 2

[0061] This comparative example provides a method for rapid activation of a PEM fuel cell stack, and the rapid activation method is based on the PEM fuel cell system provided in Example 1, comprising the following steps:

[0062] S1. Connect the fuel cell to be activated to the load, introduce air to the cathode of the fuel cell with a humidity of 80%, introduce hydrogen to the anode with a humidity of 80%, load to 565A, and perform self-humidification for 10 minutes;

[0063] S2, change the load to 0.7V for 20s, and record the corresponding first current as 295A.

[0064] S3, directly cut off the air supply, wait until the single-chip voltage drops below 0.1V, adjust the load to adjust the current to 10A, so that the fuel cell membrane electrode performs a hydrogen pump reaction, and the hydrogen pump reaction time is 5s;

[0065] S4, restore the air supply to restore the current to the first current of 295A, and record the voltage of the third single chip as 0.71V;

[0066] S5, repeating steps S3 and S4 until the voltage of the third single chip is recorded to be unchanged for three consecutive times, and repeating for a total of about 100 times;

[0067] S6. Load to 565A for self-humidification for 20 minutes to complete the activation.

[0068] The activation method time and hydrogen consumption of Example 2 and Comparative Example 1 are shown in Table 1.

[0069] Table 1

[0070] project Comparative Example 1 Example 2 Activation completion 99％ 100％ time More than 4 hours 1 hour Hydrogen consumption 4 units 0.75 units

[0071] The activation time of Example 2 of the present invention is about 1 hour, and the activation time of Comparative Example 1 is more than 4 hours (reference Figure 6 ), indicating that the activation method of the present invention greatly shortens the activation time, and the performance effect of the fuel cell stack after activation of the present invention is also higher than that of the conventional constant current activation method (reference Figure 7 ). And it can be seen from Table 1 that, compared with the conventional activation method of Comparative Example 1, the present invention can save about 81% of hydrogen consumption.

[0072] Depend on Figure 5 It can be seen that the voltage drop time of Example 2 is significantly shortened compared with Comparative Example 2; and the time of the battery with the fastest voltage drop and the battery with the slowest voltage drop in the battery stack of Example 2 is very close, while the voltage drop time in the battery stack of Comparative Example 2 varies greatly, thereby affecting the consistency of the hydrogen pump time of each battery in the battery stack; this shows that compared with the method of directly cutting off the air supply, the method of reducing the air supply in the present invention shortens the voltage drop time and improves the consistency of the activation effect of the single-piece membrane electrode in the battery stack.

[0073] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for rapid activation of a PEM fuel cell stack, characterized in that: The following steps are involved: S1. Connect the fuel cell stack to be activated to the load, introduce air into the cathode of the fuel cell, introduce hydrogen into the anode, and load the rated current or rated voltage of the fuel cell for self-humidification; S2, changing the load to the first single-chip voltage, and recording the corresponding first current; S3, greatly reducing the air supply to the cathode of the fuel cell, and when the single-chip voltage drops below the second single-chip voltage, adjusting the load to adjust the current to the second current, so that the fuel cell membrane electrode performs a hydrogen pump reaction; S4, restore the air supply to the cathode of the fuel cell to restore the current to the first current, and record the third single-chip voltage; S5, repeating steps S3 and S4 until the voltage of the third single chip is stable; S6. Load the rated current or rated voltage to the fuel cell for self-humidification to complete activation.

2. The method for rapid activation of a PEM fuel cell stack according to claim 1, characterized in that: In step S3, the second single-chip voltage is 0.01V to 0.1V, and the second current is 1 to 50A.

3. The method for rapid activation of a PEM fuel cell stack according to claim 1, characterized in that: In step S3, the hydrogen pump reaction time is 3 to 10 seconds.

4. The method for rapid activation of a PEM fuel cell stack according to claim 1, characterized in that: In step S1, the self-humidification time is 5 to 10 minutes; in step S6, the self-humidification time is 10 to 20 minutes.

5. The method for rapid activation of a PEM fuel cell stack according to claim 1, characterized in that: In step S2, the first single chip voltage is 0.7-0.8V, and the first single chip voltage is maintained for 10-60s.

6. The method for rapid activation of a PEM fuel cell stack according to claim 1, characterized in that: In step S1, the humidity of the air and hydrogen is 80% to 150%.

7. The method for rapid activation of a PEM fuel cell stack according to claim 1, characterized in that: In step S5, steps S3 and S4 are repeated 30 to 150 times.

8. The rapid activation method for a PEM fuel cell stack according to any one of claims 1 to 7, characterized in that: In step S3, substantially reducing the air supply to the cathode of the fuel cell includes: substantially reducing the air supply to the cathode of the fuel cell by controlling a bypass channel.

9. The method for rapid activation of a PEM fuel cell stack according to claim 8, characterized in that: In step S4, restoring the air supply to the cathode of the fuel cell includes: restoring the air supply to the cathode of the fuel cell by controlling a bypass channel.

10. A PEM fuel cell system, characterized in that: Based on the PEM fuel cell system, the rapid activation method according to any one of claims 1 to 9 is implemented, and the PEM fuel cell system comprises: the PEM fuel cell system comprises a fuel cell stack, an air supply branch and a hydrogen supply branch, the air supply branch is used to provide air for the fuel cell stack system, and the hydrogen supply branch is used to provide hydrogen for the fuel cell stack system; The air supply branch includes an air compressor, which is connected to the air inlet of the fuel cell stack through an air intake channel, and the air outlet of the fuel cell stack is connected to an air outlet channel. A cathode bypass channel is connected between the air intake channel and the air outlet channel, and a cathode bypass valve is provided on the cathode bypass channel.

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