Activation method of porous electrode of fuel cell and fuel cell

Abstract

The invention discloses an activation method of a porous electrode of a fuel cell and the fuel cell. The activation method comprises the following steps: providing a fuel cell with a porous carbon membrane electrode; a load is connected to carry out large-current discharge treatment on the fuel cell under the condition that the current density is greater than 2A / cm < 2 >; in the open circuit state, the external power supply performs high-potential cyclic scanning processing on the fuel cell; and connecting a load so that the fuel cell is subjected to low-voltage discharge treatment under the condition that the voltage is 0.4-0.6 V, thereby realizing the activation of the porous electrode of the fuel cell. According to the invention, the fuel cell is activated in a manner of combining high-current discharge, high-potential cyclic scanning and low-voltage discharge, so that the proton impedance and internal resistance of the cell are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cells, and in particular relates to an activation method for a porous electrode of a fuel cell and a fuel cell. Background Art

[0002] As the terminal of hydrogen energy application, proton exchange membrane fuel cell has the advantages of cleanliness, no pollution, long endurance, etc., and is used in power generation, transportation and other fields. However, before the fuel cell works, the battery must be activated to improve its performance to a stable threshold in order to give full play to the performance of the battery. At present, the commonly used activation schemes for fuel cell systems are mainly divided into two categories: offline activation and online activation.

[0003] Offline activation refers to the process of pre-activating the membrane or removing oxides and impurities on the catalyst surface in advance when the fuel cell is not discharged. Usually, methods such as boiling / fumigating the electrode and chemical treatment with H2SO4 are used. For example, in the patent with publication number CN102097631A, deionized water is continuously introduced into the gas flow channel to fully wet the membrane electrode, which is better and faster than water vapor wetting. However, this method will result in uneven distribution of water in the flow channel, and the residual liquid water will cause local flooding during loading, resulting in performance degradation.

[0004] Online activation mainly includes constant pressure / constant current activation, hydrogen pump activation, cathode starvation, CO replacement, etc. The traditional online activation methods are constant pressure activation and constant current activation, which are time-consuming and require a large amount of fuel during the activation process. The methods of hydrogen pump activation and cathode starvation can shorten the activation time, and have been increasingly used in the activation scheme of the stack system in recent years. For example, in the patent with publication number CN114447376A, an interactive hydrogen pump activation method is adopted to achieve rapid activation of the fuel cell electrode by changing the current direction applied by the DC power supply, shortening the activation time to less than 1 hour, improving efficiency, and reducing hydrogen consumption. At present, due to the high activity of porous carbon catalysts, the fuel cell catalyst carriers on the market are gradually iterating from solid carbon to porous carbon. The above scheme has a good activation effect on the traditional solid carbon carrier membrane electrode, but for the porous carbon carrier membrane electrode that is currently being used more and more widely, due to its complex porous structure, the traditional activation scheme cannot open the closed pores in the catalytic layer, resulting in some isolated platinum being unable to play an active role and unable to fully exert the performance of the electrode. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for activating a porous electrode of a fuel cell and a fuel cell to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: An embodiment of the present invention provides a method for activating a porous electrode of a fuel cell, which comprises: Providing a fuel cell having a porous carbon film electrode; Connect to the load at a current density of >2A / cm 2 Performing a high current discharge process on the fuel cell under the condition of: An external power supply is connected to perform high potential cycle scanning on the fuel cell in an open circuit state; Furthermore, a load is connected to allow the fuel cell to perform a low-voltage discharge process at a voltage of 0.4-0.6V, thereby activating the porous electrode of the fuel cell.

[0007] An embodiment of the present invention further provides a fuel cell, wherein the fuel cell is activated by at least the aforementioned activation method.

[0008] Compared with the prior art, the beneficial effect of the present invention is that the present invention activates the fuel cell by combining high current discharge + high potential cycle scanning + low voltage discharge, thereby reducing the proton impedance and internal resistance of the battery and improving the polarization curve performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] 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.

[0010] Figure 1 Schematic diagram of the activation mechanism of a fuel cell in a typical embodiment of the present invention. DETAILED DESCRIPTION

[0011] In view of the defects of the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution mainly adopts a combination of high-current discharge + external power supply scanning + constant voltage discharge: in the first step, hydrogen is introduced into the anode and humidified air is introduced into the cathode, so that the battery is discharged at high power to activate the initial performance of the battery; in the second step, the cathode gas is changed to nitrogen, and the external power supply is used to perform high-potential cycle scanning on the battery in an open circuit state; in the third step, the cathode gas is switched to air, and low-voltage constant voltage activation is performed.

[0012] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] Specifically, as one aspect of the technical solution of the present invention, a method for activating a porous electrode of a fuel cell involves: Providing a fuel cell having a porous carbon film electrode; Connect to the load at a current density of >2A / cm 2 Performing a high current discharge process on the fuel cell under the condition of: An external power supply is connected to perform high potential cycle scanning on the fuel cell in an open circuit state; Furthermore, a load is connected to allow the fuel cell to perform a low-voltage discharge process at a voltage of 0.4-0.6V, thereby activating the porous electrode of the fuel cell.

[0014] In some preferred embodiments, the activation method specifically includes: introducing hydrogen into the anode of the fuel cell and introducing air into the cathode, and then connecting a load to allow the fuel cell to perform a high current discharge treatment for 1 to 4 hours; The humidity of the gas at the anode and cathode is 50-100 RH, the stoichiometric ratio of hydrogen is 1-1.5, and the stoichiometric ratio of air is 1.5-4.

[0015] In some preferred embodiments, the voltage during the high current discharge treatment is not less than 0.4V.

[0016] The current density used in the high current discharge treatment of the present invention is >2A / cm 2 , such as 3A, 5A, 10A, etc.; high current discharge treatment can activate the initial performance of the battery and make the membrane electrode fully wetted from the inside out.

[0017] In some preferred embodiments, the activation method specifically includes: after the high current discharge treatment is completed, disconnecting the load, maintaining an open circuit state, keeping hydrogen flowing into the anode and nitrogen flowing into the cathode, and waiting for the battery voltage to drop below 0.1V, performing a high potential cycle scanning treatment on the fuel cell with an external power supply; The humidity of the gas at the anode and cathode is 0-100 RH, the flow rate of hydrogen and nitrogen is independently 0-2 slpm, the upper limit of the cyclic voltage scan is 1.2-1.5 V, the lower limit is 0.9-1 V. The scan rate is 10-100 mV / s, and the number of cycles is 50-1000.

[0018] The high potential in the high potential cyclic scanning treatment of the present invention refers to a cyclic voltage scanning upper limit of 1.2-1.5V (for example, 1.2V, 1.3V, 1.4V, 1.5V), and a lower limit of 0.9-1V (for example, 0.9V, 0.95V, 1V); the high potential cyclic scanning treatment modifies the inner and outer surfaces of the carbon carrier in the electrode, and the carbon carrier undergoes an oxidation reaction with water to form C-OH groups at defect sites that are easily electrochemically oxidized, corroding excess carbon that blocks the pore structure (including pores between carbon particles in the catalyst layer and mesopores and micropores on the porous carbon), promoting water vapor transmission in the catalyst layer, while also exposing more Pt particles in the dead zone of the catalyst layer, thereby increasing the three-phase interface sites.

[0019] Furthermore, when the catalyst carrier used in the membrane electrode of the fuel cell is hydrophobic graphitized porous carbon, the humidity of the gas at the anode and cathode is 30-100 RH, and the number of cycles is 200-1000 cycles.

[0020] Furthermore, when the catalyst carrier used in the membrane electrode of the fuel cell is hydrophilic porous carbon, the humidity of the gas at the anode and cathode is 0-50RH, and the number of cycles is 50-300.

[0021] Furthermore, the specific surface area of ​​the catalyst used in the membrane electrode of the fuel cell is less than 200m 2 / g, the number of cycles is 100~1000.

[0022] Furthermore, the catalyst used in the membrane electrode of the fuel cell has a specific surface area of ​​200-300m 2 / g, the number of cycles is 50~300.

[0023] Furthermore, the specific surface area of ​​the catalyst used in the membrane electrode of the fuel cell is greater than 300m 2 / g, the number of cycles is 50~200.

[0024] In some preferred embodiments, the activation method specifically includes: after the high-potential cyclic scanning treatment is completed, hydrogen is kept flowing into the anode and air is flowing into the cathode, and a load is connected to allow the fuel cell to perform a low-voltage discharge treatment for 1 to 4 hours; wherein the humidity of the gas at the anode and the cathode is 50 to 100 RH, the stoichiometric ratio of the hydrogen is 1 to 1.5, and the stoichiometric ratio of the air is 1.5 to 4.

[0025] The low voltage in the low-voltage discharge treatment of the present invention refers to a voltage of 0.4~0.6V (for example, 0.4V, 0.5V, 0.6V, etc.); the low-voltage discharge treatment can reduce the oxidized Pt particles, rearrange the ionomers, make the ionomer distribution more uniform, reduce the proton impedance and internal resistance, and generate more three-phase interfaces.

[0026] In some preferred embodiments, the carbon support of the catalyst in the fuel cell membrane electrode comprises hydrophobic graphitized porous carbon and / or hydrophilic porous carbon, but is not limited thereto.

[0027] In some more specific embodiments, the method for activating the porous electrode of the fuel cell comprises the following steps: (1) Hydrogen is introduced into the anode, air is introduced into the cathode, and a load is connected to discharge the battery at a constant current. The humidity of the cathode and anode gases is 50~100RH, the stoichiometric ratio of hydrogen to air is 1~1.5 and 1.5~4 respectively, and the load is connected so that the current is greater than >2A / cm 2 The discharge time is 1~4h.

[0028] (2) Disconnect the load and keep the circuit open. The anode gas remains unchanged, the cathode is switched to nitrogen, and when the battery voltage drops below 0.1V, an external power supply performs a high-potential voltage cycle scan on the battery. The gas humidity is 0-100RH, the flow rate of hydrogen and nitrogen is 0-2slpm, the upper limit of the cyclic voltage scan is 1.2-1.5V, the lower limit is 0.9-1V, the scan rate is 10-100mV / s, and the number of cycles is 50-1000cycles.

[0029] Preferably, when the catalyst carrier used in the membrane electrode is hydrophobic graphitized porous carbon, the gas humidity is 30-100 RH, and the number of cycles is 200-1000 cycles.

[0030] Preferably, when the catalyst carrier used in the membrane electrode is hydrophilic porous carbon, the gas humidity is 0-50RH, and the number of cycles is 50-300 cycles.

[0031] As a preferred embodiment, when the catalyst used in the membrane electrode has a specific surface area of ​​200 m 2 / g, the number of cycles is 100~1000 cycle; when the ratio is 200~300m 2 / g, cycle number 50~300 cycle, when the ratio is greater than 300m 2 / g, cycle number 50~200cycle.

[0032] (3) The anode gas remains unchanged, the cathode is switched back to air, and a load is connected to discharge it at a constant voltage. The gas humidity is 50~100RH, the stoichiometric ratio of hydrogen to air is 1~1.5 and 1.5~4 respectively, the voltage is 0.4~0.6V, and the discharge time is 1~4h.

[0033] The activation method provided by the present invention comprises the following steps: in the first step, hydrogen is introduced into the anode and air is introduced into the cathode, so that the battery is discharged at a large current to activate the initial performance of the battery, and the membrane electrode is fully wetted from the inside to the outside; in the second step, high-potential cyclic scanning is performed under hydrogen and nitrogen conditions to modify the inner and outer surfaces of the carbon carrier, and the carbon carrier undergoes an oxidation reaction with water to form C-OH groups at defect sites that are easily electrochemically oxidized, thereby corroding away excess carbon that blocks the pore structure (including the pores between carbon particles in the catalyst layer and the mesopores and micropores on the porous carbon), thereby promoting the water vapor transmission in the catalyst layer and also more The Pt particles in the dead zone of the catalytic layer are exposed, thereby increasing the three-phase interface sites. During the constant voltage activation process in the third step, the lower voltage can reduce the Pt particles oxidized in the second step; at the same time, the Pt particles exposed during the external power supply scanning in the second step attract the sulfonic acid groups of the ionomer, causing the ionomer to rearrange, making the ionomer distribution more uniform, reducing the proton impedance and internal resistance, and generating more three-phase interfaces; finally, the reactant water can wet the opened pores to ensure proton transmission, and when discharged from the battery, it will also take away the impurities shed during the carbon redox process, reducing the proton impedance and internal resistance. The mechanism is as follows Figure 1 shown.

[0034] Another aspect of an embodiment of the present invention further provides a fuel cell, wherein the fuel cell is activated by at least the aforementioned activation method.

[0035] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0036] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0037] Example 1 (1) Hydrogen is introduced into the anode, air is introduced into the cathode, and a load is connected to discharge the battery with a large current. The humidity of the anode and cathode gases is 80 RH, the stoichiometric ratio of hydrogen to air is 1.5 and 2.5 respectively, and the load is connected to discharge in a constant current mode with a current density of 3A / cm 2 , the discharge time is 1h.

[0038] (2) Disconnect the load and keep the circuit open. The anode gas remains unchanged, the cathode is switched to nitrogen, and when the battery voltage drops below 0.1V, the external power supply performs a high-potential cycle scan on the battery. The gas humidity is 40RH, the flow rate of hydrogen and nitrogen is 0.5slpm, the cycle scan voltage range is 1-1.5V, the scan rate is 0.05V / s, and the number of cycles is 500.

[0039] (3) The anode gas remains unchanged, the cathode is switched back to air, and a load is connected to discharge it at a low voltage. The gas humidity is 80 RH, the stoichiometric ratio of hydrogen to air is 1.5 and 2.5 respectively, the voltage is 0.5 V, and the discharge time is 1 h.

[0040] Among them, the membrane electrode is hydrophobic graphitized porous carbon.

[0041] Example 2 The method is the same as that of Example 1, except that the membrane electrode is hydrophilic porous carbon; the number of cycles in step (2) is 100, and the humidity of the gas is 20RH.

[0042] Example 3 The method is the same as in Example 1, except that the specific surface area of ​​the catalyst in the membrane electrode is 180 m 2 / g; the number of cycles in step (2) is 100, and the humidity of the gas is 30RH.

[0043] Example 4 The method is the same as in Example 1, except that the specific surface area of ​​the catalyst in the membrane electrode is 240 m 2 / g, the number of cycles in step (2) is 200, and the humidity of the gas is 30RH.

[0044] Example 5 The method is the same as in Example 1, except that the specific surface area of ​​the catalyst in the membrane electrode is 400 m 2 / g, the number of cycles in step (2) is 100, and the humidity of the gas is 30RH.

[0045] Comparative Example 1 The method is the same as in Example 1 except that step (1) is missing.

[0046] Comparative Example 2 The method is the same as in Example 1 except that step (2) is omitted.

[0047] Comparative Example 3 The method is the same as in Example 1 except that step (3) is missing.

[0048] Comparative Example 4 The method is the same as in Example 1 except that the current density in step (1) is 1.5 A / cm 2 .

[0049] Comparative Example 5 The method is the same as in Example 1, except that the voltage in step (3) is 0.7V.

[0050] Comparative Example 6 The method is the same as in Example 1, except that the voltage in step (3) is 0.3V.

[0051] Comparative Example 7 The method is the same as that of Example 1, except that the humidity of the gas at the anode and cathode in step (2) is 20 RH.

[0052] Comparative Example 8 The method is the same as in Example 1, except that the number of cycles in step (2) is 100.

[0053] Comparative Example 9 The method is the same as in Example 1, except that the number of cycles in step (2) is 1200.

[0054] Comparative Example 10 The method is the same as that of Example 2, except that the humidity of the gas at the anode and cathode in step (2) is 80 RH.

[0055] Comparative Example 11 The method is the same as that of Example 2, except that the number of cycles in step (2) is 20.

[0056] Comparative Example 12 The method is the same as that of Example 2, except that the number of cycles in step (2) is 500.

[0057] Comparative Example 13 The method is the same as that of Example 3, except that the number of cycles in step (2) is 10.

[0058] Comparative Example 14 The method is the same as that of Example 3, except that the number of cycles in step (2) is 1200.

[0059] Comparative Example 15 The method is the same as that of Example 4, except that the number of cycles in step (2) is 20.

[0060] Comparative Example 16 The method is the same as that of Example 4, except that the number of cycles in step (2) is 500.

[0061] Comparative Example 17 The method is the same as that of Example 5, except that the number of cycles in step (2) is 20.

[0062] Comparative Example 18 The method is the same as that of Example 5, except that the number of cycles in step (2) is 300.

[0063] Single battery test conditions: 1. Polarization curve performance test At battery temperature 80o C, polarization curve test was carried out under the conditions of 100RH for cathode and anode humidity, 150Kpa back pressure, and 1.5:2.5 hydrogen to air stoichiometric ratio. The current control mode was adopted, the current started from 0A, and a voltage value was recorded every 2.5A until the voltage value was less than 0.48V, and it was stable for 5 minutes at each current. After the test was completed, the power-current curve was drawn and the highest power was recorded.

[0064] 2. Internal resistance test The internal resistance meter was used for measurement, the frequency was set to 1000 Hz, and the current density of the polarization curve test was 2 A / cm 2 The impedance value.

[0065] 3. Proton conduction impedance test Battery temperature 80 o C, the humidity of anode and cathode is 100RH, the back pressure of anode and cathode is 197 / 175Kpa, hydrogen is introduced into the anode, and nitrogen is introduced into the cathode, with flow rates of 2slpm / 2slpm respectively, the test voltage is 0.2V, and the disturbance voltage is 2 mV.

[0066] The activated batteries of Examples 1-5 and Comparative Examples 1-18 were tested using the above method. The results are shown in Table 1.

[0067] Table 1 Test results of activated batteries of Examples 1-5 and Comparative Examples 1-18

[0068] From the results in Table 1, it can be seen that the performance of Examples 1-5 is significantly better than that of Comparative Examples 1-18, which shows that the three activation steps are indispensable and that appropriate condition parameters need to be selected according to the type of membrane electrode material in order to achieve a significant performance improvement effect. Specifically: Comparative Examples 1 and 4 show that the lack of step one or insufficient wetting during step one will cause the catalyst to be dry, thereby reducing the electrochemical modification effect of the carbon support in step two, failing to produce a sufficient three-phase interface, and resulting in a low maximum power; at the same time, the rearrangement of the ionomer is hindered, and the internal resistance and proton impedance are high.

[0069] Comparative Example 2 shows that the processes of Mechanism 1 and Mechanism 2 rely on the surface modification of the carbon support during the high-pressure cycle in Step 2. The unactivated Pt particles in the pores in Step 2 cannot participate in the reaction.

[0070] Comparative Examples 3 and 5 illustrate that if the oxidized Pt during high-pressure cycling is not subjected to low-pressure reduction treatment, the oxide covering the surface will hinder contact with oxygen, resulting in a decrease in polarization curve performance.

[0071] The voltage in step 3 of comparative example 6 is too low, resulting in hydrogen evolution reaction in the catalytic layer, severe corrosion of the anode catalyst, and degradation of battery performance.

[0072] Comparative Examples 7 and 10 show that humidity affects the activation effect. Too low humidity will affect the effects of Mechanism 1 and Mechanism 2, because sufficient water is required to participate in the reaction during the modification of the carbon carrier; and when the carbon carrier in the membrane electrode is hydrophilic porous carbon, too high humidity will cause excessive corrosion.

[0073] Comparative Examples 8-9 and Comparative Examples 11-18 show that the number of cycles will affect the activation effect, and different types of membrane electrode materials have different suitable ranges of cycles. Too few cycles are not enough to fully open the pores, and too many cycles will cause the catalyst layer structure to collapse. The more hydrophobic the carbon carrier in the membrane electrode or the smaller the specific surface area of ​​the catalyst, the better the effect will be if the number of cycles is less.

[0074] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0075] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the protection scope of the present invention.

Claims

1. A method for activating a porous electrode of a fuel cell, characterized in that: include: Providing a fuel cell having a porous carbon film electrode; Connect to the load at a current density of >2A / cm 2 Performing a high current discharge process on the fuel cell under the condition of: An external power supply is connected to perform high potential cycle scanning on the fuel cell in an open circuit state; Furthermore, a load is connected to allow the fuel cell to perform a low-voltage discharge process at a voltage of 0.4-0.6V, thereby activating the porous electrode of the fuel cell.

2. The activation method according to claim 1, characterized in that Specifically include: Hydrogen is introduced into the anode of the fuel cell, and air is introduced into the cathode, and then a load is connected to allow the fuel cell to perform a high current discharge process for 1 to 4 hours; The humidity of the gas at the anode and cathode is 50-100 RH, the stoichiometric ratio of hydrogen is 1-1.5, and the stoichiometric ratio of air is 1.5-4.

3. The activation method according to claim 1, characterized in that: The voltage during the high current discharge process is greater than or equal to 0.4V.

4. The activation method according to claim 1, characterized in that Specifically include: After the high current discharge process is completed, the load is disconnected, the circuit is kept open, hydrogen is passed into the anode, and nitrogen is passed into the cathode, and when the battery voltage drops below 0.1V, an external power supply is connected to perform a high potential cycle scanning process on the fuel cell; The humidity of the gas at the anode and cathode is 0~100RH, the flow rates of hydrogen and nitrogen are independently 0~2slpm, the upper limit of the cyclic voltage scan is 1.2-1.5V, the lower limit is 0.9-1V, the scan rate is 10~100mV / s, and the number of cycles is 50~1000.

5. The activation method according to claim 4, characterized in that: When the catalyst carrier used in the membrane electrode of the fuel cell is hydrophobic graphitized porous carbon, the humidity of the gas at the anode and cathode is 30-100 RH, and the number of cycles is 200-1000.

6. The activation method according to claim 4, characterized in that: When the catalyst carrier used in the membrane electrode of the fuel cell is hydrophilic porous carbon, the humidity of the gas at the anode and cathode is 0-50RH, and the number of cycles is 50-300.

7. The activation method according to claim 4, characterized in that: The specific surface area of ​​the catalyst used in the membrane electrode of the fuel cell is less than 200m 2 / g, the number of cycles is 100~1000; And / or, the catalyst used in the membrane electrode of the fuel cell has a specific surface area of ​​200-300m 2 / g, the number of cycles is 50~300; And / or, the specific surface area of ​​the catalyst used in the membrane electrode of the fuel cell is greater than 300m 2 / g, the number of cycles is 50~200.

8. The activation method according to claim 1, characterized in that Specifically include: After the high potential cyclic scanning treatment is completed, hydrogen is kept flowing into the anode, air is flowing into the cathode, and a load is connected to allow the fuel cell to perform a low voltage discharge treatment for 1 to 4 hours; wherein the humidity of the gas at the anode and cathode is 50 to 100 RH, the stoichiometric ratio of the hydrogen is 1 to 1.5, and the stoichiometric ratio of the air is 1.5 to 4.

9. The activation method according to claim 1, characterized in that: The carbon support of the catalyst in the fuel cell membrane electrode comprises hydrophobic graphitized porous carbon and / or hydrophilic porous carbon.

10. A fuel cell, characterized in that: The fuel cell is activated by at least one of the activation methods described in any one of claims 1 to 9.

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