A method for preparing a porous cathode electrode based on bubble precipitation pore formation

Abstract

The application belongs to the technical field of fuel cell membrane electrode, and specifically discloses a porous cathode electrode preparation method based on pore forming by bubble precipitation. The preparation method comprises the following steps: step 1, preparing a conventional cathode catalyst layer; step 2, assembling an electrolysis electrode structure; and step 3, electrolyzing the cathode catalyst layer, and controlling the gas distribution on the ionomer film and the pore structure of the catalyst layer generated by the catalytic site. The application controls the bubble precipitation of the catalytic site, forms pores on the ionomer film and the electrode pore structure, controls the ionomer distribution, increases the catalyst layer pores, increases the transmission channel of oxygen molecules in the catalyst layer to the catalytic site, and reduces the local and bulk mass transfer resistance of oxygen. The new porous electrode structure as a proton exchange membrane fuel cell cathode, and the proton exchange membrane and the anode form an efficient oxygen mass transfer membrane electrode, and has a wide application prospect.

Description

Technical Field

[0001] The present 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 a major bottleneck restricting 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 decrease in Pt catalyst loading, the oxygen transport problem becomes significant. In particular, the complex structure of the catalyst layer seriously hinders oxygen transport, which seriously restricts the performance in the high current density region. The oxygen transport process in the catalyst layer includes bulk transport in the pore structure and localized transport in the ultra-thin ionomer film at the catalyst interface. The molecular diffusion and Knudsen diffusion processes 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. The oxygen transport in the ionomer film follows the "adsorption-diffusion" model. Precisely 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 and ionomer distribution of the catalytic layer in the existing technology. 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-forming positions are randomly distributed, making it difficult to precisely regulate the catalytic site. Summary of the Invention

[0004] In response to 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 pore formation, which generates gas and bubbles at the catalytic site through electrolysis reaction, forms pores in the ionomer film and the pore structure of the catalytic layer, optimizes the distribution of the ionomer at the catalyst / carbon support interface, increases the oxygen transmission channel in the catalytic layer, and reduces the oxygen mass transfer resistance. The bubble precipitation pore formation method adopted in the present invention does not involve additional chemicals, so it is simple to operate and does not require template removal. Since the site where the bubbles are generated is the oxygen reduction reaction site, it can accurately form pores in the oxygen transmission channel.

[0005] In order to achieve the above object, the specific technical solutions adopted by the present invention are 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 the proton exchange membrane (PEM) to form a "PEM / CCL" half-electrode;

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

[0009] Step 3: Water electrolysis reaction is carried out on the "WE-ACL / PEM / CCL" electrode in a zero-gap single electrolyzer. Gas is generated at the cathode catalyst interface and pores are formed in the interfacial ionomer film and the pore structure of the catalyst layer. The "WE-ACL / PEM / CCL" electrode with cathode bubble pores is obtained, 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 ionomer / carbon support mass ratio (I / C) ranges from 0.6 to 0.8. If the ionomer content in the catalyst layer is too high, it can clog the pores during bubble precipitation, or the high gas pressure can destroy the original structure of the catalyst layer. If the ionomer content is too low, proton conduction can be affected.

[0011] Preferably, in step 1, the cathode catalyst layer is prepared by ultrasonically spraying, electrostatically spraying, or hot-pressing a slurry comprising 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 to 1:6.

[0012] Preferably, in step 1, the proton exchange membrane has a large thickness and strong mechanical properties, such as Nafion 212.

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

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

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

[0016] Preferably, in step 3, the electrolysis process lasts for 0.5-1 hour. If the electrolysis time is too short, the ionomer distribution cannot be adjusted and the pore structure cannot be formed; if the electrolysis time is too long, the structure of the catalytic layer is easily damaged, causing the catalyst activity 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 use of a porous cathode electrode prepared using the above-mentioned preparation method in a proton exchange membrane fuel cell. 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 surface 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 using conventional methods, specifically by ultrasonically spraying or electrostatically spraying a slurry onto the proton exchange membrane, or by hot-pressing and transferring the slurry onto 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 uses a bubble precipitation pore-forming method to pretreat the oxygen transmission channels at the catalyst site using bubbles during the electrolysis process without using additional pore-forming agents. This optimizes the ionomer distribution, increases the pore structure within the catalyst layer, and enhances oxygen transmission at the catalyst interface and pore structure. This 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 the 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 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 catalytic layer in Example 1 with and without electrolysis; in the figure, (a) is the initial catalytic layer, and (b) is the catalytic layer after electrolysis treatment.

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

[0028] The present invention will be further described below with reference to 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 formation, and the steps are as follows:

[0031] Step 1: A mixture of catalyst TEC10E30E (a commercial platinum-carbon catalyst, including a carbon support and a platinum catalyst), perfluorosulfonic acid ionomer, and a dispersing solvent is used as the initial cathode catalyst layer (CCL) slurry, which is ultrasonically sprayed onto 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 the "WE-ACL / PEM / CCL" electrode structure.

[0033] Step 3: Water electrolysis reaction was carried out on 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. A hydrogen evolution reaction occurs at the cathode catalyst interface, generating gas and creating pores in the interfacial ionomer film and the pore structure of the catalytic layer, obtaining a "WE-ACL / PEM / CCL" electrode after cathode bubble pore formation, completing the preparation of the porous cathode.

[0034] Step 4: The electrolyzed "PEM / CCL" half-electrode was rinsed with deionized water and dried; the slurry containing the catalyst TEC10E30E was then ultrasonically sprayed onto the other side of the proton exchange membrane Nafion 212 to prepare the fuel cell anode. The Pt loading was ~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 as follows: 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 the pores in the catalyst layer structure increase due to the pressure of gas evolution. Figure 3 The 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 formation, and the steps are as follows:

[0038] Step 1: A mixture of catalyst TEC10E30E, perfluorosulfonic acid ionomer, and dispersing solvent was used as the initial cathode catalyst layer (CCL) raw material and ultrasonically sprayed onto 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 was ~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 the "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 in the interface ionomer film and the pore structure of the catalytic 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 rinsed with deionized water and dried; the slurry containing the catalyst TEC10E30E was then ultrasonically sprayed onto the other side of the proton exchange membrane Nafion 212 to prepare the fuel cell anode. The Pt loading was ~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 merely an explanation of the present invention and is 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 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 the electrolysis anode electrode, assemble it with the "PEM / CCL" half-electrode to form a "WE-ACL / PEM / CCL" electrode structure; Step 3: Water electrolysis is performed on the "WE-ACL / PEM / CCL" electrode in a zero-gap single electrolyzer. Gas is generated at the cathode catalyst interface and pores are formed in the interfacial ionomer film and the pore structure of the catalyst layer. The "WE-ACL / PEM / CCL" electrode with cathode bubble pores is obtained, completing 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 electrolytic cell 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 takes 0.5-1h.

7. The 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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