A method for recovering the performance of a fuel cell

Abstract

The application discloses a kind of fuel cell performance recovery method, using humidity saturated nitrogen to the anode and cathode of fuel cell are purged, after fuel cell voltage stabilizes;Using humidity saturated hydrogen to the anode of fuel cell is purged, using humidity saturated nitrogen to the cathode of fuel cell is purged, after fuel cell voltage stabilizes, into first cycle voltammetry test, after completing first cycle voltammetry test;Adjust the gas flow of cathode, so that the gas flow of cathode and anode remains equal, carries out second cycle voltammetry test, until connecting multiple cycle voltammograms coincide.The fuel cell performance recovery method provided in the application is safer, more efficient, and has strong operability, can effectively restore the performance of fuel cell in a short time, improve the power output performance and life of fuel cell.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for recovering the performance of a fuel cell, and belongs to the technical field of fuel cells. BACKGROUND

[0002] Fuel cells are widely used in the fields of transportation and engineering machinery as clean energy. In actual application, the environment has an important influence on the performance of fuel cells. In the process of operation, the environment air is generally used, so the impurities in the air have an influence on the performance and service life of fuel cells. In the long-term operation process, the electrode catalyst surface of the fuel cell will adsorb impurities and generate an oxide film, covering the active sites of the catalyst, causing the performance of the fuel cell to decline. Especially in the application field of engineering machinery, such as heavy trucks, mining trucks, excavators and loaders, the working scene is mostly in the wild environment, and the environmental conditions are harsh, with the characteristics of high dust, high salt mist and high heat and humidity, which will have a greater influence on the performance of the fuel cell.

[0003] The commonly used method for removing the oxide film on the surface of the electrode catalyst at present is the cathode gas starvation method, that is, stopping the supply of gas to the cathode in the working state of the fuel cell, generating a low potential to reduce the oxide film on the surface of the catalyst. This method will cause a large pressure difference between the cathode and the anode, and even cause reverse polarity, which will cause irreversible damage to the fuel cell. With the increase in the application of fuel cell vehicles and engineering machinery, it is very important to recover the performance decline caused by the coverage of impurities and oxide film on the surface of the electrode catalyst in the long-term operation process, and it is necessary to design a method for removing the impurities and oxide film on the surface of the electrode catalyst, which is applied to the regular maintenance of the fuel cell in the long-term operation process and restores the performance.

[0004] The first prior art avoids the irreversible decay problem caused by the low voltage of the single battery by improving the voltage inspection to detect the lowest voltage of the single battery, but this cathode gas starvation technology will cause a large pressure difference between the cathode and the anode. A large pressure difference between the cathode and the anode will cause the film to break, causing irreversible damage to the stack. At the same time, when the cathode is starved, the anode gas will flow to the cathode, directly reacting to generate a large amount of heat, which is easy to form local hot spots, causing local irreversible damage to the membrane electrode.

[0005] The second prior art produces a lot of water in the rated current environment to provide a recovery environment for desorbing the impurities brought by the sulfides in the air on the cathode catalyst layer, and purifies the impurities, but the reduction potential is not enough to completely reduce the oxide film on the surface of the cathode catalyst layer, and the oxide film cannot be completely removed, which will reduce the recovery effect of the fuel cell.

[0006] In summary, the method of reducing the oxide on the surface of the cathode catalyst proposed by the existing patented technology cannot completely remove the oxide film on the surface of the catalyst during actual operation, and is prone to problems such as too low cathode potential, too large anode-cathode pressure difference, and gas blowby, thereby causing reverse polarity, membrane rupture, and local hot spots, causing irreversible damage to the fuel cell and posing a high risk.

[0007] Therefore, the present invention proposes a safer and more efficient fuel cell system performance recovery method to solve the above problems. Summary of the Invention

[0008] Objective: To overcome the deficiencies in the prior art, the present invention provides a method for restoring fuel cell performance.

[0009] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A method for restoring fuel cell performance comprises the following steps:

[0011] Step 1: Use humidity-saturated nitrogen to purge the anode and cathode of the fuel cell. After the fuel cell voltage stabilizes, proceed to step 2.

[0012] Step 2: Use humidity saturated hydrogen to purge the anode of the fuel cell, and use humidity saturated nitrogen to purge the cathode of the fuel cell. After the fuel cell voltage stabilizes, enter the first cyclic voltammetry test. After completing the first cyclic voltammetry test, enter step 3.

[0013] Step 3: Adjust the gas flow rate of the cathode to keep the gas flow rate of the cathode and anode equal, and perform a second cyclic voltammetry test until the multiple cyclic voltammetry curves overlap.

[0014] As a preferred solution, the step 1 includes:

[0015] Use saturated nitrogen to purge the anode and cathode of the fuel cell. Keep the gas flow F1 of the anode and cathode equal and ventilate for 5-60 minutes. When the fuel cell voltage gradually drops to close to 0 V, continue to ventilate for 5-60 minutes. After the fuel cell voltage stabilizes, proceed to step 2.

[0016] As a preferred solution, the gas flow rate F1 is 0.5*n-50*n NLPM, where n is the number of cells in the fuel cell module.

[0017] As a preferred solution, the step 2 includes:

[0018] The anode of the fuel cell is purged with saturated hydrogen, and the cathode of the fuel cell is purged with saturated nitrogen. The flow rate of saturated hydrogen introduced into the anode is set to N times the flow rate of saturated nitrogen introduced into the cathode, where N ranges from 2 to 5. The gas is introduced for 1 to 20 minutes. After the fuel cell voltage stabilizes, the first cyclic voltammetry test is performed. After the first cyclic voltammetry test is completed, step 3 is performed.

[0019] The scanning voltage range of the first cyclic voltammetry test was (0.05-1.5)*n V, and the scanning rate was set to low-speed scanning V1, with the range of V1 being 0.01-0.05 V·s -1 , V·s -1 represents the voltage scan rate, the number of cycles is 1-100 times, and n is the number of cells in the fuel cell module.

[0020] As a preferred solution, the flow rate of the humidified nitrogen gas introduced into the cathode is 0.02*n-20*n NLPM, where n is the number of cells in the fuel cell module.

[0021] As a preferred solution, the relative humidity of the humidity-saturated hydrogen and the humidity-saturated nitrogen are both greater than or equal to 100%.

[0022] As a preferred solution, the voltage range of the second cyclic voltammetry test is (0.05-1.5)*nV, the scanning rate is set to high-speed scanning V2, and the range of V2 is 0.02-0.2 V·s -1 , the number of scans is 1-100 times, and n is the number of single cells in the fuel cell module.

[0023] As a preferred solution, the fuel cell in step 1 adopts an active area of ​​25 cm 2 The number of the single-chip battery is 1, the gas flow rate F1 is 2 NLPM, the ventilation time is 5 minutes, and when the fuel cell voltage continues to drop to close to 0 V, the gas is continuously fed for 5 minutes.

[0024] As a preferred solution, the fuel cell in step 2 adopts an active area of ​​25 cm 2 The number of the monolithic battery is 1, the flow rate of the humidified nitrogen gas introduced into the cathode is 0.075 NLPM, N is 2.67, and the gas is introduced for 1 minute and 10 seconds.

[0025] As a preferred solution, the number of scans in the first cyclic voltammetry test in step 2 is 15 times.

[0026] As a preferred solution, the fuel cell in step 3 adopts an active area of ​​25 cm 2 The number of the single-chip battery is 1, and the number of scans in the second cyclic voltammetry test is 5 times.

[0027] Beneficial effects: Compared with the prior art, the method for restoring fuel cell performance provided by the present invention has the following beneficial effects:

[0028] (1) The fuel cell performance recovery method provided by the present invention adopts cyclic voltammetry in a hydrogen and nitrogen atmosphere, which does not cause reverse polarity and does not generate an excessive pressure difference between the cathode and the anode. It is safer, more efficient, and has strong operability, and can effectively restore the performance of the fuel cell in a short time.

[0029] (2) The cyclic voltammetry method designed in the present invention can reduce the oxide covering layer formed on the surface of the electrode catalyst during long-term operation, exposing more catalyst active sites, improving the catalytic activity, and thus improving the power output performance of the fuel cell.

[0030] (3) The cyclic voltammetry method designed in this invention can provide an environment for desorbing impurities from the electrode catalyst surface during the potential cycling process. During the discharge of liquid water condensed from the humidity-saturated intake air in the fuel cell, the impurities desorbed from the catalyst surface can be removed, thereby purifying the impurities adsorbed on the catalyst surface and restoring the performance of the fuel cell. At the same time, the purification of impurities on the catalyst surface, such as sulfides, can solve the problem of catalyst poisoning and thus extend the service life of the fuel cell.

[0031] (4) The method described in the present invention uses humidity-saturated gas at the anode and cathode, which can produce a large amount of liquid water environment, which can moisten the membrane, solve the performance degradation problem caused by membrane drying during long-term operation of the fuel cell, and improve the performance of the fuel cell.

[0032] (5) The method provided by the present invention can be applied to the performance recovery and regular maintenance of fuel cells during long-term use in different usage environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method for restoring the performance of a fuel cell in long-term operation according to the present invention.

[0034] Figure 2 Cyclic voltammetry curves of different scan numbers during the fuel cell performance recovery process provided by one embodiment of the present invention.

[0035] Figure 3 Polarization curves and power curves of a fuel cell before and after performance recovery provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to specific embodiments.

[0037] like Figure 1A method for restoring fuel cell performance is shown. The fuel cell to be restored is connected to an electrochemical workstation and a gas system. The gas system allows hydrogen or nitrogen to be passed through the anode of the fuel cell and nitrogen to be passed through the cathode, and includes a humidifier to adjust the relative humidity of the gas.

[0038] Cyclic voltammetry is used to restore the performance of the fuel cell. The specific steps are as follows:

[0039] Step 1: Humidity saturated nitrogen purge: Saturated nitrogen is introduced into the anode and cathode of the fuel cell for purge. The gas flow rates of the anode and cathode are kept equal. The gas flow rate is set to F1 and the gas is ventilated for 5-60 minutes. When the fuel cell voltage gradually drops to close to 0 V, the gas is continuously introduced for 5-60 minutes.

[0040] The value of F1 is set based on the number of cells in the fuel cell module. For a fuel cell module with n cells, F1 ranges from 0.5*n to 50*n NLPM (standard liters per minute). Nitrogen purging prevents the formation of a hydrogen-air interface. The water vapor in the saturated gas condenses into liquid water, which wets the membrane and prevents performance degradation caused by membrane drying during long-term fuel cell operation.

[0041] The active area of ​​the embodiment is 25cm 2 In the case of a single cell (n=1), during the humidity-saturated nitrogen purge process, the flow rate F1 was 2 NLPM. When saturated nitrogen was passed through the anode and cathode for 5 minutes, the fuel cell voltage continued to drop to nearly 0 V. The anode and cathode were kept flowing with saturated nitrogen for another 5 minutes, and the fuel cell voltage did not change.

[0042] Step 2: Introduce saturated hydrogen and nitrogen: After the fuel cell voltage stabilizes, stop purging the anode and cathode with saturated nitrogen. Saturated hydrogen is introduced to the anode, and saturated nitrogen is introduced to the cathode. The dew point temperature is set so that the relative humidity of both the saturated hydrogen and saturated nitrogen at the inlet is greater than or equal to 100%. Saturated hydrogen is introduced to the anode, and saturated nitrogen is introduced to the cathode. The gas flow rates to the anode and cathode are set according to the following two different flow modes.

[0043] Anode high flow, cathode low flow mode M1: The flow rate of saturated hydrogen at the anode is set to N times the flow rate of saturated nitrogen at the cathode, with N ranging from 2 to 5. The cathode nitrogen flow rate is F2, ranging from 0.02*n to 20*n NLPM, where n is the number of cells in the fuel cell module. The gases are passed for 1-20 minutes. After the fuel cell voltage stabilizes, the electrochemical workstation is turned on and cyclic voltammetry is performed.

[0044] Low scan rate: In the above cyclic voltammetry test, the scan voltage range is (0.05-1.5)*n V, where n is the number of cells in the fuel cell module. The scan rate is set to low scan V1, with V1 ranging from 0.01-0.05 V·s -1 , V·s -1 Indicates the voltage scan rate and the number of cycles from 1 to 100.

[0045] The gas flow rate at the anode is higher than the gas flow rate at the cathode and low-speed scanning can allow sufficient redox reaction to occur on the surface of the cathode catalyst to reduce the oxide on the surface of the cathode catalyst and desorb impurities on the surface of the cathode catalyst.

[0046] The active area of ​​the embodiment is 25 cm 2 The single-chip battery (n=1) is in the anode high flow and cathode low flow mode M1, the cathode nitrogen flow F2 is 0.075 NLPM, the N value is 2.67, and the fuel cell voltage rises to the open circuit potential after 1 minute of ventilation. The fuel cell voltage does not increase within 10 seconds. It can be considered that the fuel cell voltage is stable at the open circuit potential and enters the cyclic voltammetry test. The duration of the fuel cell in the open circuit potential state should be avoided to reduce the damage to the fuel cell caused by the high potential. In the embodiment, the cyclic voltammetry scans 15 times, and the oxidation peak near 0.6 V disappears, indicating that the impurities on the platinum surface have been oxidized and removed. Three peaks appear near 0.06 V, 0.15 V and 0.25 V, which correspond to the adsorption and desorption of hydrogen on different crystal planes of platinum, indicating that the clean Pt surface is completely exposed, such as Figure 2 In the anode high flow and cathode low flow mode M1 of step 2, the preferred cathode nitrogen flow F2 of the embodiment is 0.075 NLPM, the N value is 2.67, the ventilation is 1 minute and 10 seconds, and the number of cycles is 15.

[0047] Step 3: Anode and cathode equal flow mode M2: After completing the above low-speed scan, adjust the gas flow rate of the cathode to keep the gas flow rate of the cathode and anode equal, and perform cyclic voltammetry test.

[0048] High scan rate: In the above cyclic voltammetry test, the scan voltage range is (0.05-1.5)*nV, where n is the number of cells in the fuel cell module. The scan rate is set to high-speed scan V2, with a V2 range of 0.02-0.2 V·s -1 , scan number 1-100. When three consecutive cyclic voltammetry (CV) curves overlap, it indicates that oxides and impurities on the catalyst surface have been completely removed, exposing the clean platinum surface. The CV scan is then stopped. Increasing the cathode gas flow rate and performing high-speed scanning can generate more condensed water at the cathode, creating an environment where desorbed impurities can be discharged from the fuel cell along with the liquid water.

[0049] The active area of ​​the embodiment is 25 cm 2 In a single-cell (n=1) with equal flow rate mode M2 ​​for both the anode and cathode, the number of cycles was five. The curves for the third to fifth cycles completely overlapped, indicating that the clean Pt surface was fully exposed and impurities were completely expelled. The cyclic voltammetry scan was stopped. In step 3, the preferred number of cycles in this embodiment is five.

[0050] During long-term operation, impurities are adsorbed on the surface of the electrode catalyst. Especially in the harsh application environment of engineering machinery, including high dust, high salt fog, high humidity and heat, impurities such as sulfides and nitrides are more likely to accumulate on the cathode side, covering the catalyst surface, causing catalyst poisoning and reducing activity. Impurities adsorbed on the electrode surface can be desorbed during the cyclic voltammetry scan. Impurities can be brought out during the discharge of liquid water condensed by saturated intake air in the fuel cell. In order to solve the problem of oxide film on the surface of the electrode catalyst caused by operating cycle during the long-term operation of the fuel cell, cyclic voltammetry is used to reduce it.

[0051] It can be seen from the above technical solution that this method uses an atmosphere of hydrogen and nitrogen, which will not cause reverse polarity at low potentials and will not produce excessive pressure difference between the cathode and anode, so it is safer, more efficient, and more operational.

[0052] This invention provides a method for restoring fuel cell performance using cyclic voltammetry in a saturated hydrogen / nitrogen atmosphere. This method addresses the problem of oxide film on the surface of electrode catalysts caused by operating cycles during long-term fuel cell operation by reducing the oxide film. Saturated hydrogen is introduced into the anode of the fuel cell, and saturated nitrogen is introduced into the cathode. A potential sweep is performed during the loading cycle to reduce the oxide on the electrode catalyst surface and desorb impurities from the electrode catalyst surface. To address the problem of membrane drying and performance degradation during long-term fuel cell operation, the membrane is moistened by condensing the saturated gas in the fuel cell, creating a liquid water environment.

[0053] The method of the present invention safely and efficiently removes oxide films and adsorbed impurities, while also moistening the membrane. It can be applied to fuel cell performance restoration and regular maintenance, improving power output during long-term operation and thereby increasing the durability and lifespan of the entire unit. The method not only restores fuel cell performance but also effectively addresses the problem of fuel cell performance degradation and shortened lifespan caused by catalyst surface poisoning caused by adsorbed impurities.

[0054] Figure 2The cyclic voltammetry (CV) curves for different scan numbers during performance recovery using cyclic voltammetry for a single fuel cell embodiment are provided. In this embodiment, the CV curve for the first cycle shows a distinct oxidation peak near 0.61 V, indicating the oxidation and desorption of adsorbed impurities on the platinum surface, indicating that the catalyst is heavily covered by impurities. The peak near 0.8 V corresponds to the redox peak of the oxide Pt-Ox. In the potential range of 0.05-0.4 V, the peaks for hydrogen adsorption and desorption are smaller, indicating less exposed platinum surface. The fifth cycle curve shows an increase in current value in the potential range of 0.05-0.4 V compared to the first cycle curve. This potential range involves hydrogen adsorption and desorption on the clean platinum surface, indicating that more catalytically active sites were exposed on the platinum surface during the cyclic voltammetry scan. This is because, under the combined action of low potential and hydrogen, the oxide layer Pt-Ox covering the platinum surface is reduced, exposing the clean platinum surface and increasing catalytic activity. In the first scan, a distinct oxidation peak appeared at 0.6 V, corresponding to the oxidation and desorption of impurities adsorbed on the catalyst surface. In the fifth cyclic voltammetry curve, the peak at 0.6 V decreased, indicating that impurities on the Pt surface were being gradually removed. In the tenth cyclic voltammetry curve, the peak at 0.6 V disappeared, indicating that impurities on the catalyst surface had been completely removed. In the fifteenth cycle, a high oxidation peak appeared at 0.06 V. This was due to hydrogen permeation into the cathode under the M1 mode (high anode flow and low cathode flow), resulting in adsorption and desorption reactions on the high-energy Pt crystal facets, indicating complete removal of Pt surface coatings. After this phenomenon occurred, the flow mode was adjusted to the M2 mode with constant flow, and cyclic voltammetry scans were continued to generate more water and remove impurities from the Pt surface. In the 20th cycle, three peaks appeared near 0.06 V, 0.15 V, and 0.25 V, corresponding to hydrogen adsorption and desorption on different Pt crystal facets, indicating a completely clean Pt surface. The cycle curves from the 18th to the 20th completely overlap, and the cyclic voltammetry curve for the 20th time shows that the clean Pt surface is completely exposed, and the cyclic voltammetry scan is stopped. In this embodiment, the M1 mode is scanned 15 times, and then the M2 scan is continued for 5 times, completing the removal of oxides and impurities on the surface of the fuel cell catalyst. During the scanning process of the M1 and M2 modes, under the combined action of low potential and hydrogen, the oxide layer Pt-Ox covering the platinum surface is reduced, and at the same time, the impurities adsorbed at high potential are oxidized and carried out of the fuel cell by liquid water, exposing the clean platinum surface, completing the performance recovery of the catalyst, and then restoring the performance of the fuel cell.

[0055] from Figure 3It can be seen that compared with the polarization curve before performance recovery, the voltage loss of the polarization curve after performance recovery is reduced, the polarization is reduced, and the performance is improved. In this embodiment, the maximum power density of the fuel cell is increased from 1034 mW / cm 2 Increased to 1167 mW / cm 2 From the power-current curves before and after the performance recovery, it can be seen that after the performance recovery operation of the present invention is performed on the fuel cell, the maximum output power is significantly improved, by 13%.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for restoring fuel cell performance, characterized in that: The steps include: Step 1: Use saturated nitrogen to purge the anode and cathode of the fuel cell. After the fuel cell voltage stabilizes, proceed to step 2. Step 2: Purge the anode of the fuel cell with saturated hydrogen and the cathode of the fuel cell with saturated nitrogen. After the fuel cell voltage stabilizes, proceed to the first cyclic voltammetry test. After the first cyclic voltammetry test is completed, proceed to step 3. Step 3: Adjust the gas flow rate of the cathode to keep the gas flow rate of the cathode and anode equal, and perform a second cyclic voltammetry test until the multiple cyclic voltammetry curves overlap; Step 1 includes: purging the anode and cathode of the fuel cell with saturated nitrogen gas, maintaining the gas flow F1 at the anode and cathode equal, and ventilating for 5-60 minutes. When the fuel cell voltage gradually decreases to close to 0V, continue ventilating the gas for 5-60 minutes. After the fuel cell voltage stabilizes, proceed to step 2. The gas flow rate F1 is 0.5*n-50*n NLPM, where n is the number of cells in the fuel cell module; The step 2 comprises: The anode of the fuel cell is purged with saturated hydrogen, and the cathode of the fuel cell is purged with saturated nitrogen. The flow rate of the saturated hydrogen gas introduced into the anode is set to N times the flow rate of the saturated nitrogen gas introduced into the cathode, where N ranges from 2 to 5. The gas is introduced for 1 to 20 minutes. After the fuel cell voltage stabilizes, the first cyclic voltammetry test is performed. After the first cyclic voltammetry test is completed, step 3 is performed. The scanning voltage range of the first cyclic voltammetry test was (0.05-1.5)*n V, and the scanning rate was set to low-speed scanning V1, with V1 ranging from 0.01-0.05 V·s -1 , V·s -1 represents the voltage scan rate, the number of cycles is 1-100 times, and n is the number of cells in the fuel cell module; The flow rate of saturated nitrogen gas introduced into the cathode is 0.02*n-20*n NLPM, where n is the number of cells in the fuel cell module; The relative humidity of humidity-saturated hydrogen and humidity-saturated nitrogen is greater than or equal to 100%; The scanning voltage range of the second cyclic voltammetry test is (0.05-1.5)*nV, and the scanning rate is set to high-speed scanning V2, and the range of V2 is 0.02-0.2V·s -1 , the number of scans is 1-100 times, and n is the number of single cells in the fuel cell module.

2. A method for restoring fuel cell performance according to claim 1, characterized in that: In step 1, the fuel cell has an active area of ​​25 cm 2 The number of cells is 1, the gas flow rate F1 is 2NLPM, the ventilation time is 5 minutes, and when the fuel cell voltage continues to drop to close to 0V The gas was continuously introduced for 5 minutes.

3. The method for restoring fuel cell performance according to claim 1, characterized in that: The fuel cell in step 2 has an active area of ​​25 cm 2 The number of the monolithic battery is 1, the flow rate of the humidified nitrogen gas introduced into the cathode is 0.075 NLPM, N is 2.67, the gas is introduced for 1 minute and 10 seconds, and the number of scans in the first cyclic voltammetry test is 15 times.

4. The method for restoring fuel cell performance according to claim 1, wherein: The fuel cell in step 3 has an active area of ​​25 cm 2 The number of the single-chip battery is 1, and the number of scans in the second cyclic voltammetry test is 5 times.

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