Fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology

Abstract

The invention discloses a fuel cell membrane electrode recovery method based on a supercritical fluid and a microwave technology, and efficient and complete separation is performed during actual recovery. The complete separation of the proton exchange membrane and the perfluorosulfonic acid ionomer resin from the catalyst is successfully realized; the supercritical fluid pretreatment and microwave-assisted heating processes adopted in the invention are mild, so that the damage to the material caused by high temperature or other harsh conditions is avoided, the physicochemical properties of the separated catalyst and perfluorosulfonic acid ionomer resin are ensured, and the catalyst and the perfluorosulfonic acid ionomer resin can be repeatedly utilized; the recycling value of the material is obviously improved; in the method, the supercritical fluid not only serves as a separation medium, but also can be recycled after the process is finished, so that the influence on the environment is greatly reduced, and meanwhile, the recycling cost is also reduced.

Description

Technical Field

[0001] The invention relates to the technical field of proton exchange membrane fuel cells, and in particular to a fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology. Background Art

[0002] With the development of renewable energy technology, fuel cells have attracted widespread attention as an efficient energy conversion device. Among the various types of fuel cells, proton exchange membrane fuel cells (PEMFCs) have become a hot spot in research and application due to their high energy conversion efficiency, low emissions and fast response characteristics. One of the core components of PEMFCs is the catalyst coated membrane (CCM), which consists of a proton exchange membrane, a catalyst layer and a perfluorosulfonic acid ionomer, containing precious metals such as platinum;

[0003] However, the recycling and reuse of CCMs faces significant challenges. Conventional thermal and chemical treatment methods have problems of inefficiency and environmental pollution when separating different components in CCMs. In particular, when trying to separate proton exchange membranes and catalysts, harmful chemicals are often required for recycling, but the recycling of proton exchange membranes usually involves complex physical or chemical processes, and the recycling of catalysts requires the effective separation of perfluorosulfonic acid ionomers.

[0004] After searching, the Chinese patent publication number CN113363521A discloses a method for recovering platinum catalyst in waste membrane electrodes of proton exchange membrane fuel cells. The method mainly includes placing the waste membrane electrodes after removing the gas diffusion layer in an alcohol-water solution, separating the electrolyte membrane and the catalyst layer by microwave irradiation, wherein the alcohol solution is any one or more of methanol, ethanol, isopropanol, and ethylene glycol, the microwave irradiation time is 5-20 minutes, the temperature is 30-180°C, and the microwave power is 50-300W; and then reducing the platinum oxide to obtain the catalyst.

[0005] Therefore, the materials and catalysts recovered by traditional methods cannot be completely purified and have low utilization value.

[0006] Based on this, in order to effectively overcome the above-mentioned defects, the present application proposes a fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology. Summary of the invention

[0007] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology comprises the following steps:

[0010] S1: supercritical fluid pretreatment;

[0011] S2: microwave-assisted processing, catalyst separation and recovery;

[0012] S3: Separation and recovery of perfluorosulfonic acid ionomer resin;

[0013] S4: Remanufacturing of CCM.

[0014] The S1-S3 are processed together to obtain a catalyst;

[0015] The remanufacturing of the CCM in step S4 comprises the following steps:

[0016] S41: adding the catalyst to a mixed solvent of deionized water and isopropanol, wherein the ratio of water to isopropanol is 2:1;

[0017] S42: Add the perfluorosulfonic acid ionomer resin solution and disperse it ultrasonically at 200W for 15 minutes to obtain a catalyst slurry with a solid content controlled at 1.5%.

[0018] Preferably: supercritical fluid pretreatment 100cm 2 The CCM components are placed in a supercritical fluid reactor, 2-5 liters of methanol or ethanol or isopropanol or n-propanol are added as solvent, the pressure is set to 8-20 MPa, the temperature is 245-250°C, and maintained for 10-30 minutes to achieve the pretreatment of CCM.

[0019] Furthermore: the microwave-assisted treatment is carried out under a supercritical fluid state, by starting a microwave probe deep into the reactor, setting the power to 500-1500W, treating for 30-90 minutes, and separating the catalyst layer.

[0020] Based on the above scheme: the catalyst separation and recovery in step S2 includes the following steps:

[0021] S21: gradually reducing the pressure to normal pressure and cooling to room temperature;

[0022] S22: Use a centrifuge with a speed set at 8000-12000 rpm for 3-5 min to separate the catalyst, and wash it three times with ethanol.

[0023] A better solution among the above solutions is: when separating and recovering the perfluorosulfonic acid ionomer resin in step S3, the supernatant obtained by the first centrifugal separation is concentrated in a rotary evaporator, the temperature of the rotary evaporator is 30-60°C, the vacuum degree is 0.1 to 0.5 atmospheres, and the rotation speed is 100 to 300rpm.

[0024] As a further embodiment of the present invention, the I / C ratio of the dry weight of the perfluorosulfonic acid ionomer resin to the dry weight of the catalyst carbon carrier is 0.7-0.9.

[0025] As a further solution of the present invention: the perfluorosulfonic acid ionomer resin and the catalyst carbon carrier are ultrasonically mixed at 200W for 15 minutes, and then sheared at 5000rpm for 30 minutes. During the whole process, the slurry temperature is controlled at 10°C.

[0026] As a further solution of the present invention: the slurry ultrasonic spraying method comprises the following steps:

[0027] A1: Adjust the nozzle movement speed and discharge speed to control the anode platinum loading to 0.1 mg / c㎡ and the cathode platinum loading to 0.35 mg / c㎡. During the above-mentioned anode and cathode spraying process, the temperature of the proton membrane (thickness is 12μm, and it is the same model as the proton membrane used in the CCM before recycling) carrier is 85℃.

[0028] A2: After the anode and cathode slurry spraying is completed, a 220 μm gas diffusion layer is attached to both sides of the above catalyst membrane, loaded into the mold of a hot press, and hot-pressed at 140°C and 3 MPa pressure for 2 minutes to obtain a fuel cell membrane electrode.

[0029] As a further solution of the present invention: the membrane electrode electrical performance testing method comprises the following steps:

[0030] B1: The electrical properties of the membrane electrode are tested using a fuel cell test system. The reactants used in the system are compressed air and high-purity hydrogen. The system is equipped with an external humidification system to obtain different gas humidification effects by controlling the humidifier temperature.

[0031] B2: Before testing, MEA is activated to ensure that the Nafion resin contained in the proton exchange membrane and the catalyst layer contains sufficient water to ensure sufficient conductivity;

[0032] B3: After the working conditions are stable, control the battery to have different discharge currents or voltages. After the test, export the experimental data. The single cell of the fuel cell is composed of a membrane electrode, a plate, a sealing gasket and an end plate. The plate is an airtight hard graphite plate with a size of 50×50×3mm, and the inner side is designed as a parallel serpentine three-flow channel; the sealing gasket is an ordinary plastic gasket; a stainless steel plate is used as the end plate, and the components are tightly assembled to reduce the internal resistance of the battery. The effective area of ​​the membrane electrode in the homemade single cell is 25cm 2 ;

[0033] B4: The effective area of ​​the electrode is 25cm 2 After the membrane electrode is loaded into the single experimental cell, the single cell performance test is carried out on the test bench. In the electrochemical performance test conditions of the membrane electrode, the humidity of hydrogen and oxygen is 50% RH. The hydrogen pressure and oxygen pressure are adjusted to 0.28MPa and 0.30MPa respectively. The single cell is connected to an external constant current and constant voltage power supply, the battery temperature is raised to 80℃, and the voltage-current curve of the battery is measured.

[0034] The beneficial effects of the present invention are:

[0035] 1. The present invention is subjected to the steps of supercritical fluid pretreatment, microwave-assisted treatment, catalyst separation and recovery, perfluorosulfonic acid ionomer resin separation and recovery, and CCM remanufacturing. By comparing the polarization curve data of the CCM before recovery, it can be seen that the two membrane electrode materials have very similar power generation performances, mainly because the catalyst in the embodiment is separated by the outer ring and does not contain any impurities on the surface.

[0036] 2. The recovery method of the present invention uses supercritical fluid combined with microwave-assisted treatment, and the catalyst separated by centrifugation avoids the pollution caused by the existing use of chemical reagents to reduce the catalyst. The perfluorosulfonic acid ionomer resin obtained by rotary evaporation has high purity and no structural damage, and still has the ability of proton conduction.

[0037] 3. By comparing the main elements of the catalyst obtained by the present invention and the catalyst in the CCM before recovery, it can be seen that the catalyst obtained in the embodiment has a high purity and basically does not contain perfluorosulfonic acid ionomer resin, which shows that the method of the present invention can effectively keep the components in the waste fuel cell membrane electrode CCM unchanged and is suitable for lossless recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A flow chart of a CCM recovery method for a fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology;

[0039] Figure 2 It is an embodiment of a fuel cell membrane electrode recycling method based on supercritical fluid and microwave technology and a comparison diagram of the polarization curves of CCM before recycling. DETAILED DESCRIPTION

[0040] The technical solution of this patent is further described in detail below in conjunction with specific implementation methods.

[0041] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0042] Embodiment 1:

[0043] A fuel cell membrane electrode recycling method based on supercritical fluid and microwave technology, such as Figure 1-2 As shown, the following steps are included:

[0044] Supercritical fluid pretreatment: 100cm 2 The CCM components (cut into samples no larger than 5cm*5cm) are placed in a supercritical fluid reactor, and 2-5 liters of one or more of methanol, ethanol, isopropanol or n-propanol are added as solvents. The pressure is set to 8-20MPa and the temperature is set to 245-250°C for 10-30 minutes to achieve the pretreatment of the CCM and make the reaction more complete through high temperature and high pressure;

[0045] Microwave-assisted treatment: In the supercritical fluid state, start the microwave probe deep into the reactor, set the power to 500-1500W, treat for 30-90 minutes, separate the catalytic layer, and set a long-term high-power operation to make the reduction more thorough;

[0046] Catalyst separation and recovery: gradually reduce the pressure to normal pressure, and cool to room temperature 25°C-27°C; use a centrifuge with a speed set to 8000-12000 rpm, centrifuge for 3-5 minutes to separate the catalyst, and use ethanol for centrifugal washing 3 times (centrifugal parameters are the same as above) to obtain catalyst powder;

[0047] Separation and recovery of perfluorosulfonic acid ionomer resin: The supernatant obtained by the first centrifugal separation is concentrated in a rotary evaporator at a temperature of 30-60° C., a vacuum degree of 0.1 to 0.5 atmospheres, and a rotation speed of 100 to 300 rpm. By controlling the operation time of the rotary evaporator, a perfluorosulfonic acid ionomer resin solution with a mass fraction of 5-20% is obtained;

[0048] The present invention can obtain a catalyst with high purity and a perfluorosulfonic acid ionomer resin solution through the steps of supercritical fluid pretreatment, microwave-assisted treatment, catalyst separation and recovery, perfluorosulfonic acid ionomer resin separation and recovery, etc.

[0049] Remanufacturing of CCM: adding the catalyst obtained in the above step to a mixed solvent of deionized water and isopropanol, the ratio of water to isopropanol being 2:1, then adding the perfluorosulfonic acid ionomer resin solution obtained in the above step, dispersing at 200W ultrasonically for 15min, obtaining a catalyst slurry, wherein the solid content is controlled at 1.5%, wherein the ratio of the dry weight of the perfluorosulfonic acid ionomer resin to the dry weight of the catalyst carbon carrier (I / C ratio) is 0.7-0.9, mixing at 200W ultrasonically for 15min, then shearing at 5000rpm for 30min, controlling the slurry temperature at 10°C during the whole process, obtaining a catalyst slurry;

[0050] Ultrasonic spraying of slurry: ultrasonically spray the above slurry, adjust the nozzle movement speed and discharge speed to control the anode platinum loading to 0.1mg / c㎡ and the cathode platinum loading to 0.35mg / c㎡. During the above-mentioned cathode and anode spraying process, the temperature of the carrier of the proton membrane (thickness of 12μm, and the same model as the proton membrane used in the CCM before recycling) is 85℃. After the cathode and anode slurry spraying is completed, a 220μm gas diffusion layer is attached to both sides of the above-mentioned catalyst membrane, loaded into the mold of the hot press, and hot-pressed at 140℃ and 3MPa pressure for 2min to obtain a fuel cell membrane electrode.

[0051] Embodiment 2:

[0052] A fuel cell membrane electrode recycling method based on supercritical fluid and microwave technology, such as Figure 1-2 As shown, the following steps are included:

[0053] Supercritical fluid pretreatment: 100cm 2 The CCM components (cut into samples no larger than 5cm*5cm) are placed in a supercritical fluid reactor, and 2-5 liters of one or more of methanol, ethanol, isopropanol or n-propanol are added as solvents. The pressure is set to 5-10MPa and the temperature is 195-200°C. The temperature is maintained for 10-20 minutes to achieve the pretreatment of the CCM and make the reaction more complete through high temperature and high pressure.

[0054] Microwave-assisted treatment: In the supercritical fluid state, start the microwave probe deep into the reactor, set the power to 300-500W, treat for 20-70 minutes, separate the catalytic layer, and set a long-term high-power operation to make the reduction more thorough;

[0055] Catalyst separation and recovery: gradually reduce the pressure to normal pressure, and cool to room temperature 25°C-27°C; use a centrifuge with a speed set to 8000-12000 rpm, centrifuge for 3-5 minutes to separate the catalyst, and use ethanol for centrifugal washing 3 times (centrifugal parameters are the same as above) to obtain catalyst powder;

[0056] Separation and recovery of perfluorosulfonic acid ionomer resin: The supernatant obtained by the first centrifugal separation is concentrated in a rotary evaporator at a temperature of 30-60° C., a vacuum degree of 0.1 to 0.5 atmospheres, and a rotation speed of 100 to 300 rpm. By controlling the operation time of the rotary evaporator, a perfluorosulfonic acid ionomer resin solution with a mass fraction of 5-20% is obtained;

[0057] Remanufacturing of CCM: adding the catalyst obtained in the above step to a mixed solvent of deionized water and isopropanol, the ratio of water to isopropanol being 2:1, then adding the perfluorosulfonic acid ionomer resin solution obtained in the above step, dispersing at 100W ultrasonically for 10min, obtaining a catalyst slurry, wherein the solid content is controlled at 1.3%, wherein the ratio of the dry weight of the perfluorosulfonic acid ionomer resin to the dry weight of the catalyst carbon carrier (I / C ratio) is 0.5-0.7, mixing at 100W ultrasonically for 10min, then shearing at 3000rpm for 20min, controlling the slurry temperature at 10°C during the whole process, obtaining a catalyst slurry;

[0058] Ultrasonic spraying of slurry: ultrasonically spray the above slurry, adjust the nozzle movement speed and discharge speed to control the anode platinum loading to 0.1mg / c㎡ and the cathode platinum loading to 0.35mg / c㎡. During the above-mentioned cathode and anode spraying process, the temperature of the carrier of the proton membrane (thickness of 12μm, and the same model as the proton membrane used in the CCM before recycling) is 70℃. After the cathode and anode slurry spraying is completed, a 220μm gas diffusion layer is attached to both sides of the above-mentioned catalyst membrane, loaded into the mold of the hot press, and hot-pressed at 100℃ and 2MPa pressure for 2min to obtain a fuel cell membrane electrode.

[0059] Embodiment 3:

[0060] A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology, the fuel cell membrane electrode performance test principle, including the following steps:

[0061] The electrical properties of the membrane electrode were tested using a fuel cell test system. The reactants used in the system are compressed air and high-purity hydrogen. The system is equipped with an external humidification system, and different gas humidification effects are obtained by controlling the humidifier temperature. Before the test, the MEA is activated first, the purpose of which is to make the proton exchange membrane and the Nafion resin contained in the catalyst layer contain sufficient water to ensure sufficient conductivity. After the working conditions are stable, the battery is controlled to have different discharge currents or voltages. After the test, the experimental data is exported. The single cell of the fuel cell consists of a membrane electrode, a plate, a sealing gasket and an end plate. The plate uses an airtight hard graphite plate with a size of 50×50×3mm, and the inner side is designed as a parallel serpentine three-flow channel; the sealing gasket uses an ordinary plastic gasket; a stainless steel plate is used as the end plate, and the components are tightly assembled to reduce the internal resistance of the battery. The effective area of ​​the membrane electrode in the homemade single cell is 25cm 2 The effective area of ​​the electrode is 25cm 2 After the membrane electrode is installed in the single experimental cell, the single cell performance test is carried out on the test bench. In the electrochemical performance test conditions of the membrane electrode, the humidity of hydrogen and oxygen is 50% RH, the hydrogen pressure and oxygen pressure are adjusted to 0.28MPa and 0.30MPa respectively, the single cell is connected to an external constant current and constant voltage power supply, the battery temperature is raised to 80℃, and the voltage-current curve of the battery is measured.

[0062] Embodiment 4:

[0063] A fuel cell membrane electrode recycling method based on supercritical fluid and microwave technology, the main elements of the catalytic species are compared, as shown in Table 1, which is a comparison of the main elements of the catalyst obtained in Example 1 and the catalyst in the CCM before recycling. According to Table 1, it can be seen that:

[0064] Treated by Example 1, and Figure 2 By comparison, the two membrane electrodes have very similar power generation performance, mainly because the catalyst in Example 1 is separated by the outer ring and does not contain any impurities on the surface; in addition, the obtained perfluorosulfonic acid ionomer resin has high purity and no structural damage, and still has the ability to conduct protons. By comparing the main elements of the catalyst obtained in Example 1 and the catalyst in the CCM before recovery, it can be seen that the catalyst obtained in Example 1 has high purity and basically does not contain perfluorosulfonic acid ionomer resin.

[0065]

[0066] Table 1

[0067] Comparative Example 1:

[0068] The main elements of the catalyst in the CCM obtained in Example 1 and Example 2 were compared before and after recovery, and the comparison results are shown in Table 2:

[0069]

[0070] Table 2

[0071] According to the comparison, it can be known that under different operating parameters, the CCM prepared by the recovery methods of Example 1 and Example 2 contains less perfluorosulfonic acid ionomer. It can be seen that the recovery of membrane electrode by the method of the present invention can achieve a better recovery effect.

[0072] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A fuel cell membrane electrode recycling method based on supercritical fluid and microwave technology, It is characterized in that The following steps are involved: S1: supercritical fluid pretreatment; S2: microwave-assisted processing, catalyst separation and recovery; S3: Separation and recovery of perfluorosulfonic acid ionomer resin; S4: Remanufacturing of CCM; S5: Membrane electrode electrical performance test. The S1-S3 are processed together to obtain a catalyst; The remanufacturing of the CCM in step S4 comprises the following steps: S41: adding the catalyst to a mixed solvent of deionized water and isopropanol, wherein the ratio of water to isopropanol is 2:1; S42: Add the perfluorosulfonic acid ionomer resin solution and disperse it ultrasonically at 200W for 15 minutes to obtain a catalyst slurry with a solid content controlled at 1.5%.

2. According to claim 1, a fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology, It is characterized in that Supercritical fluid pretreatment 100cm 2 The CCM components are placed in a supercritical fluid reactor, 2-5 liters of methanol or ethanol or isopropanol or n-propanol are added as solvent, the pressure is set to 8-20 MPa, the temperature is 245-250°C, and maintained for 10-30 minutes to achieve the pretreatment of CCM.

3. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to claim 2, It is characterized in that The microwave-assisted treatment is carried out under a supercritical fluid state by starting a microwave probe that penetrates deep into the reactor, setting the power to 500-1500W, and treating for 30-90 minutes to separate the catalyst layer.

4. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to claim 3, It is characterized in that The catalyst separation and recovery in step S2 comprises the following steps: S21: gradually reduce the pressure to normal pressure and cool to room temperature 25°C-27°C; S22: Use a centrifuge with a speed set at 8000-12000 rpm for 3-5 min to separate the catalyst, and wash it three times with ethanol.

5. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to claim 4, It is characterized in that When the perfluorosulfonic acid ionomer resin is separated and recovered in step S3, the supernatant obtained by the first centrifugal separation is concentrated in a rotary evaporator at a temperature of 30-60° C., a vacuum degree of 0.1 to 0.5 atmospheres, and a rotation speed of 100 to 300 rpm.

6. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to claim 5, It is characterized in that The I / C ratio of the dry weight of the perfluorosulfonic acid ionomer resin / the dry weight of the catalyst carbon support is 0.7-0.

9.

7. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to claim 6, It is characterized in that The perfluorosulfonic acid ionomer resin and the catalyst carbon carrier were ultrasonically mixed at 200 W for 15 min, and then sheared at 5000 rpm for 30 min. The slurry temperature was controlled at 10° C. during the whole process.

8. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to any one of claims 1 to 7, It is characterized in that The slurry ultrasonic spraying method comprises the following steps: A1: Adjust the nozzle movement speed and discharge speed to control the anode platinum loading to 0.1 mg / c㎡ and the cathode platinum loading to 0.35 mg / c㎡. During the above-mentioned anode and cathode spraying process, the temperature of the proton membrane carrier is 85℃. A2: After the anode and cathode slurry spraying is completed, a 220 μm gas diffusion layer is attached to both sides of the above catalyst membrane, loaded into the mold of a hot press, and hot-pressed at 140°C and 3 MPa pressure for 2 minutes to obtain a fuel cell membrane electrode.

9. A fuel cell membrane electrode recovery method based on supercritical fluid and microwave technology according to any one of claims 1 to 8, It is characterized in that The membrane electrode electrical performance test method includes the following steps: B1: The electrical properties of the membrane electrode are tested using a fuel cell test system. The reactants used in the system are compressed air and high-purity hydrogen. The system is equipped with an external humidification system to obtain different gas humidification effects by controlling the humidifier temperature. B2: Before testing, MEA is activated to ensure that the Nafion resin contained in the proton exchange membrane and the catalyst layer contains sufficient water to ensure sufficient conductivity; B3: After the working conditions are stable, control the battery to have different discharge currents or voltages. After the test, export the experimental data. The single cell of the fuel cell is composed of a membrane electrode, a plate, a sealing gasket and an end plate. The plate is an airtight hard graphite plate with a size of 50×50×3mm, and the inner side is designed as a parallel serpentine three-flow channel; the sealing gasket is an ordinary plastic gasket; a stainless steel plate is used as the end plate, and the components are tightly assembled to reduce the internal resistance of the battery. The effective area of ​​the membrane electrode in the homemade single cell is 25cm 2 ; B4: The effective area of ​​the electrode is 25cm 2 After the membrane electrode is loaded into the single experimental cell, the single cell performance test is carried out on the test bench. In the electrochemical performance test conditions of the membrane electrode, the humidity of hydrogen and oxygen is 50% RH. The hydrogen pressure and oxygen pressure are adjusted to 0.28MPa and 0.30MPa respectively. The single cell is connected to an external constant current and constant voltage power supply, the battery temperature is raised to 80℃, and the voltage-current curve of the battery is measured.

Images