Porous cathode electrode preparation method based on bubble precipitation pore forming

Abstract

The invention belongs to the technical field of fuel cell membrane electrodes, and particularly discloses a porous cathode electrode preparation method based on bubble precipitation pore forming. The preparation method comprises the following steps: step 1, preparing a conventional cathode catalyst layer; 2, assembling an electrolysis electrode structure; and step 3, electrolyzing the cathode catalyst layer, and regulating and controlling the distribution of the ionomer film and the pore structure of the catalyst layer by the gas generated by the catalytic sites. According to the invention, by precisely regulating and controlling the separation of bubbles at the catalytic sites and performing pore forming on an ionomer film and an electrode pore structure, the distribution of ionomers is regulated and controlled, the pores of the catalytic layer are increased, transmission channels for oxygen molecules in the catalytic layer to reach the catalytic sites are increased, and the local and bulk phase mass transfer resistance of oxygen is reduced. The formed novel porous electrode structure is used as a cathode of a proton exchange membrane fuel cell, forms an efficient oxygen mass transfer membrane electrode with a proton exchange membrane and an anode, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of fuel cell membrane electrodes, and in particular relates to a method for preparing a porous cathode electrode based on bubble precipitation and pore formation. Background Art

[0002] The cost of proton exchange membrane fuel cells is an important bottleneck problem that restricts their commercial development. Reducing the amount of precious metal Pt-based catalysts in the cathode catalyst layer is an important way to solve this problem. However, with the reduction of Pt catalyst loading, the oxygen transport problem becomes significant, especially the complex structure of the catalyst layer seriously hinders oxygen transport, which seriously restricts the performance in the high current density area. The oxygen transport process in the catalyst layer includes bulk transport in the pore structure and local transport in the ultra-thin ionomer film at the catalyst interface. The molecular diffusion and Knudsen diffusion process in the pore structure of the catalyst layer are related to the pore size distribution. Increasing the pore structure is the key to reducing the bulk mass transfer resistance; oxygen transport in the ionomer film follows the "adsorption-diffusion" model. Accurately adjusting the distribution of the ionomer film and strengthening the oxygen transport at the three-phase interface of the ionomer, catalyst and carbon carrier are currently effective solutions to improve the performance of proton exchange membrane fuel cells.

[0003] According to the search, there have been some studies on the regulation of the pore structure of the catalytic layer and the distribution of ionomers in the prior art. The main method is the template method. This method requires the selection of a suitable template agent, and has problems such as high cost, complex operation, and difficulty in removing the template. At the same time, the pore-making positions are randomly distributed, making it difficult to precisely regulate the catalytic site. Summary of the invention

[0004] In view of the deficiencies in the prior art, the main purpose of the present invention is to provide a method for preparing a porous cathode electrode based on bubble precipitation and pore formation, wherein gas is precipitated and bubbles are generated at the catalytic site through electrolysis reaction, pores are formed in the ionomer film and the pore structure of the catalytic layer, the distribution of the ionomer at the catalyst / carbon carrier interface is optimized, the transmission channel of oxygen in the catalytic layer is increased, and the oxygen mass transfer resistance is reduced. The bubble precipitation and pore formation method adopted in the present invention does not involve additional chemicals, so the operation is simple, and there is no difficulty in removing the template. Since the site where the bubble is generated is the oxygen reduction reaction site, it is possible to accurately form pores for the oxygen transmission channel.

[0005] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0006] A method for preparing a porous cathode electrode based on bubble precipitation and pore formation comprises the following steps:

[0007] Step 1: Prepare a conventional cathode catalyst layer (CCL) on one side of a proton exchange membrane (PEM) to form a "PEM / CCL" half-electrode;

[0008] Step 2: Using an electrode material with oxygen evolution (OER) performance as an electrolysis anode electrode (WE), assembling it and the "PEM / CCL" half-electrode to form a "WE-ACL / PEM / CCL" electrode structure;

[0009] Step 3: The "WE-ACL / PEM / CCL" electrode is subjected to water electrolysis reaction in a zero-gap single electrolyzer. Gas is generated at the cathode catalyst interface and pores are formed in the interface ionomer film and the pore structure of the catalyst layer to obtain the "WE-ACL / PEM / CCL" electrode after cathode bubble pore formation, thus completing the preparation of the porous cathode electrode.

[0010] Preferably, in step 1, the cathode catalyst layer is a low Pt loading catalyst layer, and the Pt loading is less than 0.2 mg Pt cm -2 , the mass ratio of ionomer to carbon carrier (I / C) is in the range of 0.6-0.8. If the ionomer content in the catalyst layer is too high, the ionomer will be blocked in the pores during the bubble precipitation process, or the original structure of the catalyst layer will be destroyed due to the high gas pressure; if the ionomer content is too low, it will affect proton conduction.

[0011] Preferably, in step 1, the cathode catalyst layer is prepared by ultrasonically spraying, electrostatically spraying, or hot pressing a slurry containing a catalyst, an ionomer, and a dispersion solvent onto a proton exchange membrane. The ionomer is a perfluorosulfonic acid ionomer, and the dispersion solvent is water and ethanol, with a water-to-alcohol ratio of 1:1-1:6.

[0012] Preferably, in step 1, the proton exchange membrane has a greater thickness and stronger mechanical properties, such as Nafion212.

[0013] Preferably, in step 2, the electrolysis anode electrode is an Ir / IrOx plated titanium mesh.

[0014] Preferably, in step 3, the cathode of the electrolysis process undergoes hydrogen evolution (HER) process, and the zero-gap single electrolyzer assembly torque is 1-2 N·m. If the assembly torque is too large, the anode will squeeze the proton exchange membrane to cause perforation of the proton exchange membrane. If the assembly torque is too small, the zero-gap single electrolyzer will leak.

[0015] Preferably, in step 3, the cathode current during the electrolysis process is 0.5-2A·cm -2 If the current is too small, the gas pressure generated is small and will not have a significant effect on the morphology of the ionomer; if the current is too large, the gas pressure generated is too large and will damage the catalyst layer structure.

[0016] Preferably, in step 3, the electrolysis process lasts for 0.5-1 h. If the electrolysis time is too short, it is not enough to adjust the ionomer distribution and the pore structure cannot be formed; if the electrolysis time is too long, it is easy to damage the structure of the catalyst layer and cause the activity of the catalyst to decay.

[0017] Another object of the present invention is to provide a porous cathode electrode prepared by the above preparation method.

[0018] Another object of the present invention is to provide the application of the porous cathode electrode prepared by the above preparation method in a proton exchange membrane fuel cell. The application method is: remove the "PEM / CCL" structure in the "WE-ACL / PEM / CCL" electrode after the cathode bubble pores prepared in step 3, prepare an anode catalyst layer on the other side of the proton exchange membrane, and obtain a proton exchange fuel cell membrane electrode "FC-ACL / PEM / CCL" containing a porous cathode. The anode catalyst layer is prepared by conventional methods, specifically by ultrasonic spraying, electrostatic spraying, or hot pressing transfer of the slurry to the proton exchange membrane. The composition of the slurry can be the same as or different from that of the cathode catalyst layer.

[0019] Compared with the prior art, the present invention adopts the method of bubble precipitation pore formation, uses bubbles in the electrolysis process to pretreat the oxygen transmission channel at the catalyst site, and does not use additional pore-forming agents, optimizes the ionomer distribution, increases the pore structure in the catalyst layer, and enhances the oxygen transmission in the catalyst interface and pore structure, which has the following beneficial effects:

[0020] 1. The pore structure of the ionomer film in the cathode catalyst layer prepared by the present invention is increased, and the ionomer distribution is optimized, which is beneficial to reducing the local mass transfer resistance of oxygen in the catalyst layer.

[0021] 2. The pore structure in the cathode catalyst layer prepared by the present invention is increased, which is beneficial to reducing the oxygen gas phase mass transfer resistance in the catalyst layer.

[0022] 3. The porous cathode prepared by the present invention can be used as a high-efficiency membrane electrode cathode structure of a proton exchange membrane fuel cell to increase the current density in a high current density region.

[0023] 4. The preparation method of the present invention is simple, low-cost, does not introduce additional chemicals, and avoids the impact of pollution on performance.

[0024] 5. The present invention can well control the distribution of the ionomer film and the size of the pore structure of the catalyst layer by adjusting the electrolysis current and the electrolysis time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1: Atomic force microscope (AFM) images of the morphology of the ionomer film on the Pt substrate in Example 1 with and without electrolysis; in the figure, (a) is the initial ionomer film, and (b) is the ionomer film after electrolysis treatment.

[0026] Figure 2 : Scanning electron microscope (SEM) images of the pore structure of the catalyst layer in Example 1 with and without electrolysis; in the figure, (a) is the initial catalyst layer, and (b) is the catalyst layer after electrolysis treatment.

[0027] Figure 3 : Cell polarization curves with and without electrolysis in Example 1. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] This embodiment is based on the preparation of porous cathode electrodes and proton exchange membrane fuel cell membrane electrodes by ionomer bubble pore formation, and the steps are as follows:

[0031] Step 1: A mixture of catalyst TEC10E30E (a commercial platinum-carbon catalyst, including a carbon carrier and a platinum catalyst), perfluorosulfonic acid ionomer and a dispersion solvent is used as an initial cathode catalyst layer (CCL) slurry, which is ultrasonically sprayed on one side of the proton exchange membrane Nafion 212 to form a "PEM / CCL" half electrode. The Pt loading of the half electrode catalyst layer is ~0.11 mg Pt cm -2 , I / C is 0.6.

[0032] Step 2: Select the IrO2-plated titanium mesh as the electrolytic anode, use deionized water and isopropyl alcohol to ultrasonically clean the electrolytic anode, and then assemble the electrolytic anode and the "PEM / CCL" half electrode to form a "WE-ACL / PEM / CCL" electrode structure.

[0033] Step 3: Water electrolysis reaction of the "WE-ACL / PEM / CCL" electrode in a zero-gap single electrolyzer with a torque of 1 N·m and an electrolysis current of 0.5 A·cm -2 The electrolysis time is 30 minutes. Hydrogen evolution reaction occurs at the cathode catalyst interface, generating gas and forming pores in the interface ionomer film and the pore structure of the catalyst layer to obtain the "WE-ACL / PEM / CCL" electrode after cathode bubble formation, completing the preparation of the porous cathode.

[0034] Step 4: The "PEM / CCL" half-electrode after electrolysis was washed with deionized water and dried; then the slurry containing the catalyst TEC10E30E was ultrasonically sprayed on the other side of the proton exchange membrane Nafion 212 to prepare the fuel cell anode, with a Pt loading of ~0.05 mg Pt cm -2 , I / C is 0.6, and a proton exchange membrane fuel cell membrane electrode containing a porous cathode is obtained.

[0035] The morphology of the ionomer film on the Pt substrate before and after electrolysis is shown in Figure 2. Figure 1 As shown, Figure 1 (a) is the initial ionomer film, Figure 1 (b) is the ionomer film after electrolysis in Example 1. It can be seen that the ionomer film has obvious pore structure. The pore structure of the cathode catalyst layer before and after electrolysis in Example 1 is as follows: Figure 2 As shown, Figure 2 (a) is the initial cathode catalyst layer, Figure 2 (b) is the cathode catalyst layer after electrolysis treatment. It can be seen that due to the pressure of gas evolution, the pores in the catalyst layer structure increase. Figure 3 Comparison of the battery polarization curves before and after cathode electrolysis treatment in Example 1 shows that the current density increases significantly in the high current region due to the improvement of the oxygen transmission capacity at the interface.

[0036] Example 2

[0037] This embodiment is based on the preparation of porous cathode electrodes and proton exchange membrane fuel cell membrane electrodes by ionomer bubble pore formation, and the steps are as follows:

[0038] Step 1: A mixture of catalyst TEC10E30E, perfluorosulfonic acid ionomer and dispersing solvent is used as the initial cathode catalyst layer (CCL) raw material, which is ultrasonically sprayed on one side of the proton exchange membrane Nafion 212 to form a "PEM / CCL" half electrode. The Pt loading of the half electrode catalyst layer is ~0.11 mg Pt cm -2 , I / C is 0.6.

[0039] Step 2: Select the IrO2-plated titanium mesh as the electrolytic anode, use deionized water and isopropyl alcohol to ultrasonically clean the electrolytic anode, and then assemble the electrolytic anode and the "PEM / CCL" half electrode to form a "WE-ACL / PEM / CCL" electrode structure.

[0040] Step 3: Electrolysis of the "WE-ACL / PEM / CCL" electrode in a zero-gap single electrolyzer with a torque of 1 N·m and an electrolysis current of 2 A·cm -2The electrolysis time is 30 minutes. Gas is generated at the cathode catalyst interface and pores are formed on the interface ionomer film and the pore structure of the catalyst layer to obtain the "WE-ACL / PEM / CCL" electrode after cathode bubble pore formation, completing the preparation of the porous cathode.

[0041] Step 4: The "PEM / CCL" half-electrode after electrolysis was washed with deionized water and dried; then the slurry containing the catalyst TEC10E30E was ultrasonically sprayed on the other side of the proton exchange membrane Nafion 212 to prepare the fuel cell anode, with a Pt loading of ~0.05 mg Pt cm -2 , I / C is 0.6, and a proton exchange membrane fuel cell membrane electrode containing a porous cathode is obtained.

[0042] The changes in the pore structure of the polymer film and the catalyst layer and the cathode current density before and after electrolysis in this embodiment are the same as those in Example 1.

[0043] This specific implementation is only an explanation of the present invention, not a limitation of the present invention. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a porous cathode electrode based on bubble precipitation and pore formation, characterized in that: The following steps are involved: Step 1: Prepare a conventional cathode catalyst layer on one side of the proton exchange membrane to form a "PEM / CCL" half electrode; Step 2: Use an electrode material with oxygen evolution performance as an electrolytic anode electrode, assemble it with a "PEM / CCL" half-electrode to form a "WE-ACL / PEM / CCL" electrode structure; Step 3: Perform water electrolysis reaction on the "WE-ACL / PEM / CCL" electrode in a zero-gap single electrolyzer, generate gas at the cathode catalyst interface and create pores in the interface ionomer film and the pore structure of the catalyst layer, obtain the "WE-ACL / PEM / CCL" electrode after cathode bubble pore creation, and complete the preparation of the porous cathode electrode.

2. The method for preparing a porous cathode electrode based on bubble precipitation and pore formation according to claim 1, characterized in that: In step 1, the cathode catalyst layer is a low Pt loading catalyst layer, and the Pt loading is less than 0.2 mg Pt cm -2 , the ionomer / carbon support mass ratio ranges from 0.6 to 0.

8.

3. The method for preparing a porous cathode electrode based on bubble precipitation and pore formation according to claim 1, characterized in that: In step 1, the cathode catalyst layer is prepared by ultrasonically spraying or electrostatically spraying a slurry containing a catalyst, an ionomer and a dispersing solvent onto a proton exchange membrane, or by hot pressing and transferring the slurry onto the proton exchange membrane.

4. The method for preparing a porous cathode electrode based on bubble precipitation and pore formation according to claim 1, characterized in that: In step 2, the electrolysis anode electrode is an Ir / IrOx plated titanium mesh.

5. The method for preparing a porous cathode electrode based on bubble precipitation and pore formation according to claim 1, characterized in that: In step 3, hydrogen evolution occurs at the cathode during the electrolysis process, and the assembly torque of the zero-gap single electrolyzer is 1-2 N·m.

6. The method for preparing a porous cathode electrode based on bubble precipitation and pore formation according to claim 1, characterized in that: In step 3, the cathode current of the electrolysis process is 0.5-2A·cm -2 The electrolysis process lasts for 0.5-1h.

7. A porous cathode electrode prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the porous cathode electrode prepared by the preparation method according to any one of claims 1 to 6 in a proton exchange membrane fuel cell.

9. The use according to claim 8, characterized in that: The application method is as follows: remove the "PEM / CCL" structure in the "WE-ACL / PEM / CCL" electrode after the cathode bubble pores prepared in step 3, prepare an anode catalyst layer on the other side of the proton exchange membrane, and obtain a proton exchange membrane fuel cell membrane electrode containing a porous cathode.

10. The use according to claim 9, characterized in that: The anode catalyst layer is prepared by ultrasonically spraying or electrostatically spraying the slurry onto the proton exchange membrane, or by hot pressing and transferring the slurry onto the proton exchange membrane.

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