Preparation method of membrane electrode of proton exchange membrane fuel cell and membrane electrode

Abstract

The invention discloses a preparation method of a proton exchange membrane fuel cell membrane electrode and a membrane electrode, and the preparation method comprises the following steps: spraying a mixed solution of a platinum carbon catalyst and a PTFE emulsion on the surface of a transfer printing substrate, and drying to obtain the transfer printing substrate loaded with a catalyst layer precursor on the surface; calcining the transfer substrate loaded with the catalyst layer precursor on the surface to obtain a transfer substrate loaded with a catalyst layer on the surface; and spraying the ionomer solution to the surface of the catalyst layer on the transfer substrate, pasting a proton exchange membrane on the surface of the catalyst layer, and stripping the transfer substrate after hot pressing to obtain the proton exchange membrane fuel cell membrane electrode. The catalyst layer on the membrane electrode has higher mechanical strength, can prevent the carbon carrier from falling off and being corroded in the operation process, has a stronger carbon corrosion resistance effect after high-temperature treatment, is excellent in continuous operation stability and durability, and has a good application prospect in the field of proton exchange membrane fuel cells.

Description

Technical Field

[0001] The invention relates to a preparation method of a proton exchange membrane fuel cell membrane electrode and the membrane electrode, belonging to the technical field of proton exchange membrane fuel cells. Background Art

[0002] Proton exchange membrane fuel cells have the advantages of zero emissions, high energy conversion efficiency, low temperature rapid start, and convenient output power adjustment. They are a new generation of energy conversion devices with great development prospects. At the same time, the perfluorosulfonic acid proton exchange membrane with small size, stable chemical properties, high proton conductivity, gas separation, and recyclable use is selected as the solid electrolyte, which has practicality and good safety. Proton exchange membrane fuel cells have good application prospects in automobile internal combustion engines, small household appliances, and portable power generation equipment.

[0003] As we all know, PEMFCs widely use platinum-based precious metals as catalysts on the cathode side, but the reserves of platinum are small, the platinum loading requirement on the cathode oxygen reduction reaction side is high, and platinum metal is easily passivated by carbon corrosion, which also leads to an increase in the cost of catalyst replacement in PEMFCs. Although there are various alloy catalysts, such as intermetallic compounds and high entropy alloys, platinum catalysts are still the most economical and mature cathode catalysts, so reducing the cost of PEMFCs needs to start from other aspects.

[0004] At present, the most common platinum-carbon catalyst is to load the precious metal platinum on ordinary amorphous carbon materials. When making membrane electrodes, the catalyst is often combined with the proton exchange membrane by spraying or printing. However, there is a lack of interaction between the carbon carriers. During operation, the carbon carriers will move, fall off, and agglomerate. These phenomena will cause the local potential of the membrane electrode to increase, resulting in local corrosion of the carbon carriers. The loaded platinum particles will also become passivated or even poisoned as the carrier corrodes and cannot play a catalytic role, ultimately leading to a decrease in the durability of the catalyst. Therefore, the key issue in the development of cathode oxygen reduction reaction catalysts in proton exchange membrane fuel cells is how to improve the stability and durability of operation and reduce costs by extending the service life. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a proton exchange membrane fuel cell membrane electrode and a membrane electrode. The catalytic layer on the membrane electrode has higher mechanical strength, can prevent the carbon carrier from falling off and corroding during operation, and has a stronger anti-carbon corrosion effect after high-temperature treatment, and has excellent continuous operation stability and durability, and has good application prospects in the field of proton exchange membrane fuel cells.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a proton exchange membrane fuel cell membrane electrode comprises the following steps:

[0008] Spraying a mixture of platinum-carbon catalyst and PTFE emulsion onto the surface of the transfer substrate, and drying to obtain a transfer substrate with a catalyst layer precursor loaded on the surface;

[0009] calcining the transfer substrate with the catalyst layer precursor loaded on the surface to obtain the transfer substrate with the catalyst layer loaded on the surface;

[0010] The ionomer solution is sprayed onto the catalyst layer surface on the transfer substrate and a proton exchange membrane is attached to the catalyst layer surface. The transfer substrate is peeled off after hot pressing to obtain a proton exchange membrane fuel cell membrane electrode.

[0011] Preferably, the mixed solution of platinum-carbon catalyst and PTFE emulsion is obtained by dispersing platinum-carbon catalyst and PTFE emulsion in alcohol solution;

[0012] Wherein, the ratio of platinum carbon catalyst, PTFE emulsion and alcohol solution is (5-8) mg: (0.5-2) mg: (1-5) ml;

[0013] And the platinum content in the platinum-carbon catalyst is 15-30%;

[0014] The PTFE content in the PTFE emulsion is 50-70%.

[0015] Preferably, the drying condition is: 60-80°C.

[0016] Preferably, the calcination conditions are: nitrogen or inert gas atmosphere, 750-900° C., 1-3 h.

[0017] Preferably, the ionomer solution is obtained by dispersing a Nafion solution in an alcohol solution;

[0018] Wherein, the ratio of Nafion solution to alcohol solution is (30-50) mg: (1-5) ml;

[0019] The mass ratio of the perfluorosulfonic acid polymer in the Nafion solution to the carbon carrier in the platinum-carbon catalyst is (0.2-1):1.

[0020] Preferably, the alcohol liquid used in the mixed solution of the platinum-carbon catalyst and the PTFE emulsion and the alcohol liquid used in the ionomer solution are both isopropanol.

[0021] Preferably, the hot pressing conditions are: 90-120°C, 800-1200kpa.

[0022] A proton exchange membrane fuel cell membrane electrode is prepared by any of the above methods.

[0023] The beneficial effects of the present invention are:

[0024] A stable and flat catalyst layer is obtained by calcination, so that the carbon carrier of the catalyst layer has a certain mechanical strength. Then, the catalyst layer is completely transferred directly to the surface of the proton exchange membrane through overall transfer. This method largely avoids the problem of carbon carrier shedding and corrosion during long-term operation of the battery, and can improve the durability of the catalyst. At the same time, due to the uniform distribution of carbon materials, the catalyst and the proton exchange membrane are closely combined, the proton conductivity is enhanced, and the membrane electrode impedance is significantly reduced. Compared with the catalyst layer prepared by direct spraying, the carbon material in the catalyst layer prepared by the transfer method has a strong interaction force, and the preparation process accompanied by the doping of F elements will further improve the durability of the carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM image of the catalyst layer of the membrane electrode prepared in Example 1 after 50,000 cycles of accelerated durability testing;

[0026] Figure 2 This is a SEM image of the catalyst layer of the membrane electrode prepared in Control Example 2 after 50,000 cycles of accelerated durability testing;

[0027] Figure 3 This is a SEM image of the catalytic layer of the membrane electrode prepared in Control Example 1 after 50,000 cycles of accelerated durability testing;

[0028] Figure 4 These are Raman spectra images of the catalyst layer of the membrane electrode prepared in Example 1 before (left area) and after (right area) 50,000 cycles of accelerated durability testing;

[0029] Figure 5 These are Raman spectroscopic images of the catalyst layer of the membrane electrode prepared in Control Example 1 before (left area) and after (right area) 50,000 cycles of accelerated durability testing;

[0030] Figure 6 The Raman spectra images of the catalyst layer of the membrane electrode prepared in Control Example 2 before (left area) and after (right area) the 50,000 cycles accelerated durability test;

[0031] Figure 7 This is a comparison diagram of the graphitization degree of the carbon material in the catalyst layer on the membrane electrode after the accelerated durability test of Example 1 and Comparative Examples 1 and 2;

[0032] Figure 8 This is a comparison of the carbon corrosion degree of the carbon material in the catalyst layer on the membrane electrode after the accelerated durability test of Example 1 and Comparative Examples 1 and 2;

[0033] Fig. 9This is a comparison chart of the initial performance of a single cell having a membrane electrode prepared in Example 1 and the performance after 50,000 cycles of accelerated durability testing;

[0034] Fig.10 The initial performance comparison diagram of the single cell with the membrane electrode prepared in Control Example 1 and the performance comparison diagram after 50,000 cycles of accelerated durability test;

[0035] Fig.11 The initial performance comparison diagram of the single cell with the membrane electrode prepared in Control Example 2 and the performance comparison diagram after 50,000 cycles of accelerated durability test;

[0036] Fig.12 The figures are a comparison of the initial performance of single cells having membrane electrodes prepared in Example 1 and Comparative Examples 1-3 and a comparison of the performance after 50,000 cycles of accelerated durability testing. DETAILED DESCRIPTION

[0037] The present invention will be specifically described below in conjunction with the accompanying drawings and embodiments.

[0038] Example 1

[0039] This embodiment provides a method for preparing a membrane electrode for a proton exchange membrane fuel cell, and the specific steps are as follows: 2 ml of isopropanol, 6.25 mg of a commercially available 20% JM Pt / C catalyst, and 1 mg of a PTFE emulsion (60%) are homogenized by ultrasound to obtain an ink-like slurry. A sprayer Siansonic UC 320 is used to spray a quartz sheet (3 cm×3 cm) to spray the slurry onto the surface of the quartz sheet. The spraying process is carried out under the standard protocol of the equipment, the drying temperature is 70°C, and the spraying area is 2.5 cm×2.5 cm. The sprayed quartz sheet loaded with the catalytic layer was calcined at 700°C for 2 hours in a tube furnace under nitrogen protection. After naturally cooling to room temperature, the quartz sheet was taken out, 40 mg of Nafion (5%) solution was dispersed in 2 ml of isopropanol, and the solution was sprayed on the catalytic layer surface of the quartz sheet in the same way. The proton exchange membrane was then covered on the catalytic layer on the sprayed quartz sheet surface and hot pressed at a temperature of 100°C and a pressure of 900 kPa. After the hot pressing was completed, the quartz sheet was peeled off to obtain the desired membrane electrode.

[0040] Comparative Example 1

[0041] The difference from Example 1 is that no PTFE emulsion is added to the slurry, and the proton exchange membrane is directly prepared by spraying the slurry.

[0042] Comparative Example 2

[0043] The difference from Example 1 is that no PTFE emulsion is added to the slurry.

[0044] Comparative Example 3

[0045] The difference from Example 1 is that the proton exchange membrane is directly prepared by spraying the slurry, but hot pressing transfer is not used.

[0046] In the preparation of a single cell, both the cathode and the anode use carbon paper with a gas diffusion layer.

[0047] Characterization results

[0048] Scanning electron microscopy (SEM) characterization

[0049] The scanning electron microscope (SEM) was derived using a TM3000 model electron microscope to analyze the prepared membrane electrode. Figure 1 The figure shows the cathode side membrane electrode surface prepared in Example 1. After 50,000 cycles of accelerated durability testing, no obvious catalyst agglomeration was observed, and the carbon carrier did not fall off or move on a large scale. Figure 2 The figure shows the surface of the membrane electrode prepared without adding PTFE (Control Example 2). After the same accelerated durability test, agglomeration occurred and the carbon material fell off significantly. Figure 3 The figure shows the surface of the membrane electrode prepared by the traditional spraying method (control example 1), where more obvious agglomeration and movement of carbon materials can be seen. This phenomenon proves that the addition of PTFE and the membrane electrode prepared by the hot pressing transfer method have excellent stability and durability.

[0050] Raman spectroscopy characterization

[0051] A 532 nm laser emitter was used to perform Raman spectroscopy analysis on the samples. Figure 4 The figure shows the Raman spectrum of the membrane electrode obtained in Example 1 after 50,000 cycles of accelerated durability test. It can be seen that the degree of graphitization of the catalyst treated at high temperature increases, and the catalytic stability is improved. After the accelerated durability test, the defect of the catalytic layer on the surface of the membrane electrode increases slightly. Figure 5 This is the Raman spectrum of the membrane electrode obtained in control example 1 before and after accelerated durability testing. The graphitization degree of the carbon carrier of the platinum-carbon catalyst itself is not high. After the durability test, the degree of defect increases significantly and the carbon corrosion is serious. Figure 6 The Raman spectra of the membrane electrode obtained in control example 2 before and after the accelerated durability test are shown. By comparison, it can be seen that the carbon corrosion phenomenon of the membrane electrode prepared by the traditional spraying method is more serious. Figure 7 This is a comparison chart of the graphitization degree of the carbon material in the catalytic layer on the membrane electrode after the accelerated durability test of Example 1 and Control Examples 1 and 2. It can be seen that Example 1 has the best graphitization degree and excellent conductive efficiency. Figure 8 This is a comparison chart of the carbon corrosion degree of the catalytic layer carbon material on the membrane electrode after the accelerated durability test of Example 1 and Control Examples 1 and 2. The carbon corrosion degree of Example 1 is the lowest. This is because the additional addition of PTFE leads to the doping of F element, which improves the corrosion resistance of the carbon material.

[0052] Single cell performance characterization

[0053] The performance test was conducted under a standard proton exchange membrane fuel cell system, with a test temperature of 80°C, an anode hydrogen flow rate of 0.3L / min, a cathode oxygen flow rate of 0.4L / min, a back pressure of 1.5bar, and 100% humidification. Fig. 9 It can be seen from the performance diagram that the membrane electrode prepared by the preparation method in Example 1 has the best performance of 1.07W / cm 2 The performance of the membrane electrode prepared by the conventional spraying method in control example 1 was poor, at 901 mW / cm 2 ( Fig.10 The overall performance of the membrane electrode prepared in control example 2 without adding PTFE is lower than that in example 1, which is 920 mW / cm 2 ( Fig.11 ). The performance of the membrane electrode prepared by direct spraying with PTFE added in control example 3 was the worst, at 465 mW / cm 2 ( Fig.12 ), because the additional PTFE causes the conductivity to decrease and the performance cannot reach a usable level.

[0054] Single cell stability characterization

[0055] The durability of the electrocatalyst carrier was accelerated using the following method: the test temperature was 80°C, the anode hydrogen flow rate was 0.3L / min, the cathode argon flow rate was 0.4L / min, the back pressure was 1bar, and the humidification was 100%; the electrochemical workstation was used to perform a cyclic scan at a scan rate of 500mV / s between 1.0-1.5V. Fig.12 It can be seen that the peak performance of the membrane electrode prepared in the control example 2 is attenuated by 23.6% after 50,000 cycles of accelerated endurance test, and the peak performance of the membrane electrode prepared in the control example 1 is attenuated by 26.3% after 50,000 cycles of accelerated endurance test. Fig. 9 The peak performance of the membrane electrode prepared in Example 1 only decays by 12.2%, while the performance of Control Example 3 is very poor and has no practical value. This confirms that the addition of PTFE and the preparation of the membrane electrode by hot pressing transfer can significantly improve the stability of the membrane electrode.

[0056] The above is only a preferred implementation of the patent 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 principle of the patent of the present invention. These improvements and modifications should also be regarded as the scope of protection of the patent of the present invention.

Claims

1. A method for preparing a proton exchange membrane fuel cell membrane electrode, characterized in that: The steps include: Spraying a mixture of platinum-carbon catalyst and PTFE emulsion onto the surface of the transfer substrate, and drying to obtain a transfer substrate with a catalyst layer precursor loaded on the surface; The transfer substrate with a catalyst layer precursor loaded on its surface is calcined to obtain a transfer substrate with a catalyst layer loaded on its surface; the ionomer solution is sprayed onto the catalyst layer surface on the transfer substrate and a proton exchange membrane is attached to the catalyst layer surface; the transfer substrate is peeled off after hot pressing to obtain a proton exchange membrane fuel cell membrane electrode.

2. The method for preparing a proton exchange membrane fuel cell membrane electrode according to claim 1, characterized in that: The mixed solution of platinum-carbon catalyst and PTFE emulsion is obtained by dispersing platinum-carbon catalyst and PTFE emulsion in alcohol solution; Wherein, the ratio of platinum carbon catalyst, PTFE emulsion and alcohol solution is (5-8) mg: (0.5-2) mg: (1-5) ml; And the platinum content in the platinum-carbon catalyst is 15-30%; The PTFE content in the PTFE emulsion is 50-70%.

3. The method for preparing a proton exchange membrane fuel cell membrane electrode according to claim 1, characterized in that: The drying condition is: 60-80°C.

4. The method for preparing a proton exchange membrane fuel cell membrane electrode according to claim 1, characterized in that: The calcination conditions are: nitrogen or inert gas atmosphere, 750-900° C., 1-3 h.

5. The method for preparing a proton exchange membrane fuel cell membrane electrode according to claim 2, characterized in that: The ionomer solution is obtained by dispersing a Nafion solution in an alcohol solution; Wherein, the ratio of Nafion solution to alcohol solution is (30-50) mg: (1-5) ml; The mass ratio of the perfluorosulfonic acid polymer in the Nafion solution to the carbon carrier in the platinum-carbon catalyst is (0.2-1):

1.

6. The method for preparing a proton exchange membrane fuel cell membrane electrode according to claim 5, characterized in that: The alcohol solution used in the mixed solution of the platinum-carbon catalyst and the PTFE emulsion and the alcohol solution used in the ionomer solution are both isopropanol.

7. The method for preparing a proton exchange membrane fuel cell membrane electrode according to claim 1, characterized in that: The hot pressing conditions are: 90-120° C., 800-1200 kPa.

8. A proton exchange membrane fuel cell membrane electrode, characterized in that: The method is prepared by any one of claims 1 to 7.

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