A method for improving the microstructure of a polymer electrolyte membrane fuel cell catalyst layer

Abstract

The application specifically relates to a method for improving the microstructure of a polymer electrolyte membrane fuel cell catalytic layer, which comprises the following steps: preparing a catalyst slurry; coating the catalyst slurry on carbon paper with a microporous gas diffusion layer and drying; (3) microwave heating treatment of the carbon paper; pasting the two sides of a polymer electrolyte membrane to the catalytic layer of two pieces of carbon paper respectively to obtain a first composite layer structure; hot pressing the first composite layer structure between two pieces of protective film, cooling, and obtaining a membrane electrode with optimized structure. The application is aimed at the problems of large mass transfer resistance of O2 and ions through the catalyst-polymer interface, active site covering or embedding and the like in the membrane electrode catalytic layer under the actual working condition of PEMFCs, microwave heating treatment technology is adopted to treat the catalytic layer, the ionomer covered on the surface of the catalytic layer can be melted, the accessibility of O2 and protons can be improved, more catalytic active sites can be exposed, and the output performance of the PEMFCs can be improved.

Description

Technical Field

[0001] This invention relates to the field of polymer electrolyte membrane fuel cell technology, and more specifically to a method for improving the microstructure of the catalyst layer in polymer electrolyte membrane fuel cells. Background Technology

[0002] Polymer electrolyte membrane fuel cells (PEMFCs), the primary carrier of the hydrogen energy industry, have long suffered from a shortage of core materials, the most crucial of which is the catalyst. Currently, the precious metal Pt / C is the most effective catalyst in the membrane electrode catalytic layer of PEMFCs, but Pt is limited in reserves and expensive on Earth. Therefore, reducing the amount of Pt used in the catalyst layer is a pressing issue that needs to be addressed for key materials in PEMFCs.

[0003] Traditional methods for preparing catalyst layers mainly involve mixing and dispersing the catalyst, binder, and ionic conductor in a dispersion medium to form a catalyst slurry. This slurry is then applied to a gas diffusion layer or polymer electrolyte membrane using methods such as coating, spraying, and casting. Clearly, catalyst layers prepared using traditional methods often have active sites on the catalyst surface masked or embedded by the polymer ionic conductor, increasing the mass transfer resistance of O2 and ions across the catalyst-polymer interface and resulting in low catalyst utilization. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention aims to provide a method for improving the microstructure of the catalyst layer in polymer electrolyte membrane fuel cells (PEMFCs). The method employs microwave heat treatment technology to treat the catalyst layer, which melts the ionomer covering its surface, improves the contact state between the polymer ionic conductor and the catalyst, enhances the accessibility of O2 and ions, exposes more catalytic active sites, and thereby improves the output performance of PEMFCs.

[0005] The objective of this invention is achieved through the following technical solution: a method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell, comprising the following steps:

[0006] (1) Preparation of catalyst slurry;

[0007] (2) The catalyst slurry is coated onto carbon paper with a microporous gas diffusion layer; then the carbon paper coated with the catalyst slurry is dried to obtain carbon paper with a catalyst layer.

[0008] (3) Place the carbon paper obtained in step (2) in a microwave reactor and perform microwave heating treatment;

[0009] (4) Two pieces of carbon paper with catalytic layers that have been microwave-heated are bonded to the two sides of the polymer electrolyte membrane to obtain the first composite layer structure;

[0010] (5) The first composite layer structure obtained in step (4) is sandwiched between two protective films to obtain the second composite layer structure; the second composite layer structure is hot-pressed and then cooled to obtain the membrane electrode with optimized structure.

[0011] Furthermore, in step (1), the catalyst and polymer ionic conductor are mixed, a dispersant is added, and the mixture is ultrasonically treated and stirred to obtain a uniformly dispersed catalyst slurry.

[0012] Furthermore, in step (1), the catalyst is a Pt / C catalyst.

[0013] Furthermore, in step (1), the polymer ionic conductor is a perfluorosulfonic acid-based polymer (Nafion solution); the dispersant is at least one of methanol, ethanol, isopropanol and water.

[0014] Furthermore, in step (1), the mass ratio of the polymer ionic conductor to the catalyst is 0.2-1.0.

[0015] Furthermore, in step (1), the dispersant is a water-isopropanol mixed dispersant, and the volume ratio of water to isopropanol is 0.1-10.

[0016] Furthermore, in step (1), the concentration of the catalyst in the dispersant is 2-4 mg / mL.

[0017] Furthermore, in step (2), the carbon paper coated with catalyst slurry is vacuum dried for 2-18 hours. The catalyst loading in the catalyst layer is calculated based on the mass difference of the carbon paper before and after the catalyst is sprayed.

[0018] Furthermore, in step (2), a perfluorosulfonic acid-based polymer layer is coated onto the catalytic layer of the carbon paper.

[0019] Furthermore, in step (3), the microwave heating power is 200-1000 W, and the microwave heating time is 2-30 minutes. By employing the above process to microwave-heat carbon paper with a catalytic layer, the Nafion layer covering the catalyst surface in the catalytic layer breaks down due to microwave heat treatment, exposing more catalyst active sites, thereby improving the output performance of PEMFCs and effectively enhancing the catalyst utilization rate.

[0020] Furthermore, in step (3), the microwave heating atmosphere is nitrogen, argon and helium, and the microwave heating method is intermittent microwave heating, continuous microwave heating or a mixture of intermittent and continuous microwave heating.

[0021] Furthermore, in step (5), the hot pressing pressure is 0.2-1.0 MPa, the hot pressing temperature is 110-150 ℃, and the hot pressing time is 1-5 minutes.

[0022] The beneficial effects of this invention are as follows: Addressing the problems of high mass transfer resistance of O2 and ions through the catalyst-polymer interface and the masking or embedding of active sites in the membrane electrode catalytic layer of PEMFCs under actual operating conditions, this invention employs microwave heating technology to treat the catalytic layer. This melts the ionomer covering its surface, improving the accessibility of O2 and protons, exposing more catalytic active sites, and thus improving the output performance of PEMFCs. Furthermore, the method for improving the microstructure of the polymer electrolyte membrane fuel cell catalytic layer in this invention is simple and controllable, making it suitable for large-scale industrial applications. Attached Figure Description

[0023] Figure 1 The image shows the SEM characterization of the optimized catalyst layer prepared according to Example 1.

[0024] Figure 2 The image shows the SEM and EDX elemental distribution of the optimized catalyst layer prepared according to Example 1.

[0025] Figure 3 The diagram shows the oxygen reduction activity and cyclic voltammetry curves of the half-cell with optimized catalytic layer fabricated according to Example 1.

[0026] Figure 4 The image shows the polarization curve of the fuel cell based on the membrane electrode fabricated in Example 1. Detailed Implementation

[0027] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0028] In an embodiment of the present invention, a method for improving the microstructure of the catalyst layer of a polymer electrolyte membrane fuel cell includes the following steps:

[0029] (1) Preparation of catalyst slurry;

[0030] (2) The catalyst slurry is coated onto carbon paper with a microporous gas diffusion layer; then the carbon paper coated with the catalyst slurry is dried to obtain carbon paper with a catalyst layer.

[0031] (3) Place the carbon paper obtained in step (2) in a microwave reactor and perform microwave heating treatment;

[0032] (4) Two pieces of carbon paper that have been microwave heated are respectively placed on the two sides of the polymer electrolyte membrane, and the side of the two pieces of carbon paper with the catalytic layer is respectively attached to the two sides of the polymer electrolyte membrane to obtain the first composite layer structure;

[0033] (5) The first composite layer structure obtained in step (4) is sandwiched between two PTFE protective films to obtain the second composite layer structure; the second composite layer structure is hot-pressed and then cooled to obtain the membrane electrode with optimized structure.

[0034] Furthermore, in step (1), the catalyst and polymer ionic conductor are mixed, a dispersant is added, and the mixture is ultrasonically treated and stirred to obtain a uniformly dispersed catalyst slurry.

[0035] Furthermore, in step (1), the catalyst is a Pt / C catalyst. The catalyst may be a commercially available carbon-supported Pt (Pt / C) catalyst with a Pt loading of 0.1~2.0 mg. Pt / cm 2 .

[0036] Furthermore, in step (1), the polymer ionic conductor is a perfluorosulfonic acid-based polymer. The perfluorosulfonic acid-based polymer is also used as a binder. The dispersant is at least one of methanol, ethanol, isopropanol, and water.

[0037] In some embodiments of the present invention, in step (1), the mass ratio of the polymer ionic conductor to the catalyst is 0.2-1.0.

[0038] In some embodiments of the present invention, in step (1), the dispersant is a water-isopropanol mixed dispersant, wherein the volume ratio of water to isopropanol is 0.1-10.

[0039] In some embodiments of the present invention, in step (1), the concentration of the catalyst in the dispersant is 2-4 mg / mL.

[0040] In some embodiments of the present invention, in step (2), the carbon paper coated with catalyst slurry is vacuum dried for 2-18 hours, and the catalyst loading in the catalyst layer is calculated based on the mass difference of the carbon paper before and after the catalyst is sprayed.

[0041] The method of coating the catalyst slurry onto the microporous gas diffusion layer or polymer electrolyte membrane can be achieved by spraying, casting, or scraping.

[0042] In some embodiments of the present invention, in step (2), after the carbon paper is dried, a perfluorosulfonic acid-based polymer layer is coated on the catalytic layer of the carbon paper.

[0043] In some embodiments of the present invention, in step (3), the microwave heating power is 200-1000 W and the microwave heating time is 2-30 minutes.

[0044] In some embodiments of the present invention, in step (3), the microwave heating atmosphere is nitrogen, argon and helium, and the microwave heating method is intermittent microwave heating, continuous microwave heating or a mixture of intermittent and continuous microwave heating. Example

[0045] In this embodiment, a method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell includes the following steps:

[0046] (1) Take 30.0 mg of Pt / C catalyst, add 2.00 mL of deionized water, 1.00 mL of Nafion solution with a mass fraction of 5 wt%, and 8.00 mL of isopropanol, and perform ultrasonic treatment and stirring to obtain catalyst slurry;

[0047] (2) The catalyst slurry is sprayed onto carbon paper with a microporous gas diffusion layer; then the carbon paper with the catalyst slurry is dried to obtain carbon paper with a catalyst layer.

[0048] (3) The carbon paper obtained in step (2) was placed in a microwave reactor and subjected to microwave heating treatment. The microwave heating power was 900 W and the microwave heating time was 30 minutes. The carbon paper with optimized catalyst layer microstructure was obtained. The scanning electron microscope image and elemental distribution are shown in the figure. Figure 1-2 As shown;

[0049] (4) Two pieces of carbon paper that have been microwave heated are respectively placed on the two sides of the polymer electrolyte membrane, and the side of the two pieces of carbon paper with the catalytic layer is respectively attached to the two sides of the polymer electrolyte membrane to obtain the first composite layer structure;

[0050] (5) The first composite layer structure obtained in step (4) is sandwiched between two PTFE protective films to obtain the second composite layer structure; the second composite layer structure is hot-pressed and then cooled to obtain the membrane electrode with optimized structure.

[0051] Furthermore, in step (2), the carbon paper coated with the catalyst slurry is vacuum dried for 10 hours. Based on the mass difference of the carbon paper before and after catalyst coating, the catalyst loading in the catalyst layer is calculated, and the Pt loading in the catalyst layer is 0.2 mg / cm³. 2 .

[0052] Furthermore, in step (3), nitrogen is used as the microwave heating atmosphere, and the microwave heating method is continuous microwave heating. The carbon paper with the catalyst layer is placed in the microwave reactor for heating.

[0053] Furthermore, in step (5), the hot pressing pressure is 0.5 MPa, the hot pressing temperature is 130 °C, and the hot pressing time is 2 minutes.

[0054] In this embodiment, Figure 1 The SEM image of the optimized catalyst layer prepared for this embodiment shows that after microwave heating, the Nafion coating on the catalyst surface melts and cracks.

[0055] Figure 2 The images show the SEM and EDX elemental distribution of the optimized catalyst layer prepared according to this embodiment. Figure 2 'a' is the SEM image. Figure 2 b, c, and d are the elemental distribution diagrams of F, C, and Pt, respectively. It can be seen that after microwave treatment, C and Pt elements did not significantly accumulate, while F element was significantly enriched at the crack edge. This indicates that the F-containing Nafion layer was cracked due to microwave heat treatment, exposing more catalyst active sites.

[0056] The redox reaction performance of carbon paper with a catalyst layer before and after microwave treatment was tested in 0.1 mol / L perchloric acid solution using a three-electrode system. The test results are as follows: Figure 3 As shown. Figure 3 This image shows the oxygen reduction activity diagram and cyclic voltammetry curve of the optimized catalytic layer half-cell fabricated according to this embodiment. Figure 3 As can be seen, after 30 minutes of microwave heat treatment, the optimized catalyst layer at 0.2 V... vs. The current density at RHE reaches 51.43 mA / cm². 2 It is higher than that of the untreated catalyst layer (40.87 mA / cm). 2 At 0.2 V vs. RHE). Through Figure 3 The cyclic voltammetry curves (b) were used to calculate the electrochemical active area (ECSA) of the catalyst. The ECSA of the catalyst layer after microwave heat treatment for 30 minutes reached 68.75 m. 2 / g, higher than ECSA (36.64 m) without microwave treatment. 2 / g).

[0057] Two carbon paper sheets with optimized catalyst layer microstructures, a polymer electrolyte membrane, and two PTFE protective membranes were hot-pressed together to form a membrane electrode assembly (MEA). The performance of a single fuel cell was then tested. The hydrogen flow rate was 200 sccm, the oxygen flow rate was 300 sccm, both hydrogen and oxygen were 100% humidified, the back pressure was 0.1 MPa, and the cell operating temperature was 70℃. The measured results are as follows: Figure 4 As shown. Figure 4 The fuel cell polarization curve of the membrane electrode fabricated according to this embodiment shows that the performance of the fuel cell membrane electrode is greatly improved after microwave heat treatment for 30 minutes, with a maximum power density of 1.29 W / cm³. 2 The untreated catalyst layer had a membrane electrode peak power density of 1.14 W / cm². 2 . Example

[0058] In this embodiment, a method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell includes the following steps:

[0059] (1) Take 30.0 mg of Pt / C catalyst, add 2.00 mL of deionized water, 1.00 mL of Nafion solution with a mass fraction of 5 wt%, and 8.00 mL of isopropanol, and perform ultrasonic treatment and stirring to obtain catalyst slurry;

[0060] (2) The catalyst slurry is sprayed onto carbon paper with a microporous gas diffusion layer; then the carbon paper with the catalyst slurry is dried to obtain carbon paper with a catalyst layer.

[0061] (3) The carbon paper obtained in step (2) was placed in a microwave reactor and subjected to microwave heating treatment. The microwave heating power was 900 W and the microwave heating time was 30 minutes. The carbon paper with optimized catalyst layer microstructure was obtained. The scanning electron microscope image and elemental distribution are shown in the figure. Figure 1-2 As shown;

[0062] (4) Two pieces of carbon paper that have been microwave heated are respectively placed on the two sides of the polymer electrolyte membrane, and the side of the two pieces of carbon paper with the catalytic layer is respectively attached to the two sides of the polymer electrolyte membrane to obtain the first composite layer structure;

[0063] (5) The first composite layer structure obtained in step (4) is sandwiched between two PTFE protective films to obtain the second composite layer structure; the second composite layer structure is hot-pressed and then cooled to obtain the membrane electrode with optimized structure.

[0064] Furthermore, in step (2), the carbon paper coated with the catalyst slurry is vacuum dried for 10 hours. Based on the mass difference of the carbon paper before and after catalyst coating, the catalyst loading in the catalyst layer is calculated, and the Pt loading in the catalyst layer is 0.2 mg / cm³. 2 .

[0065] The rest of this embodiment is similar to that of Embodiment 1, and will not be repeated here. Example

[0066] In this embodiment, a method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell includes the following steps:

[0067] (1) Take 30.0 mg of Pt / C catalyst, add 1.00 mL of deionized water, 0.50 mL of Nafion solution with a mass fraction of 5 wt%, and 9.50 mL of isopropanol, and perform ultrasonic treatment and stirring to obtain catalyst slurry;

[0068] (2) The catalyst slurry is sprayed onto carbon paper with a microporous gas diffusion layer; then the carbon paper with the catalyst slurry is dried to obtain carbon paper with a catalyst layer; a Nafion layer is sprayed onto the catalyst layer of the carbon paper; spraying a Nafion layer can improve ion conductivity, improve gas transport, optimize the three-phase interface and regulate the microstructure of the catalyst layer.

[0069] (3) The carbon paper obtained in step (2) is placed in a microwave reactor and subjected to microwave heating treatment. The microwave heating power is 900 W and the microwave heating time is 30 minutes to obtain carbon paper with optimized catalyst layer microstructure.

[0070] (4) Two pieces of carbon paper that have been microwave heated are respectively placed on the two sides of the polymer electrolyte membrane, and the side of the two pieces of carbon paper with the catalytic layer is respectively attached to the two sides of the polymer electrolyte membrane to obtain the first composite layer structure;

[0071] (5) The first composite layer structure obtained in step (4) is sandwiched between two PTFE protective films to obtain the second composite layer structure; the second composite layer structure is hot-pressed and then cooled to obtain the membrane electrode with optimized structure.

[0072] Furthermore, in step (2), the carbon paper coated with the catalyst slurry is vacuum dried for 10 hours. Based on the mass difference of the carbon paper before and after catalyst coating, the catalyst loading in the catalyst layer is calculated, and the Pt loading in the catalyst layer is 0.2 mg / cm³. 2 .

[0073] The rest of this embodiment is similar to that of Embodiment 1, and will not be repeated here.

[0074] The specific embodiments described above are further illustrations of the technical solution and beneficial effects of the present invention, and are not intended to limit the implementation methods. For those skilled in the art, any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell, characterized in that: Includes the following steps: (1) The catalyst and the polymer ion conductor are mixed, a dispersant is added, and the mixture is subjected to ultrasonic treatment and stirring to obtain a uniformly dispersed catalyst slurry. The catalyst is a Pt / C catalyst; the polymer ion conductor is a perfluorosulfonic acid-based polymer; and the dispersant is at least one of methanol, ethanol, isopropanol and water. (2) The catalyst slurry is coated onto carbon paper with a microporous gas diffusion layer; then the carbon paper coated with the catalyst slurry is dried to obtain carbon paper with a catalyst layer. (3) Place the carbon paper obtained in step (2) in a microwave reactor and perform microwave heating treatment. The microwave heating power is 200-1000W and the microwave heating time is 2-30 minutes. (4) Two pieces of carbon paper with catalytic layers that have been microwave-heated are bonded to the two sides of the polymer electrolyte membrane to obtain the first composite layer structure; (5) The first composite layer structure obtained in step (4) is sandwiched between two protective films to obtain the second composite layer structure; the second composite layer structure is hot-pressed and then cooled to obtain the membrane electrode with optimized structure.

2. The method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell according to claim 1, characterized in that: In step (1), the mass ratio of the polymer ionic conductor to the catalyst is 0.2-1.

0.

3. The method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell according to claim 1, characterized in that: In step (1), the dispersant is a water-isopropanol mixed dispersant, and the volume ratio of water to isopropanol is 0.1-10.

4. The method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell according to claim 1, characterized in that: In step (2), the carbon paper coated with catalyst slurry is vacuum dried for 2-18 hours. The catalyst loading in the catalyst layer is calculated based on the mass difference of the carbon paper before and after the catalyst is sprayed.

5. The method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell according to claim 1, characterized in that: In step (2), a perfluorosulfonic acid-based polymer layer is coated onto the catalytic layer of the carbon paper.

6. The method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell according to claim 1, characterized in that: In step (3), the microwave heating atmosphere is nitrogen, argon and helium, and the microwave heating method is intermittent microwave heating, continuous microwave heating or a mixture of intermittent and continuous microwave heating.

7. The method for improving the microstructure of the catalyst layer in a polymer electrolyte membrane fuel cell according to claim 1, characterized in that: In step (5), the hot pressing pressure is 0.2-1.0 MPa, the hot pressing temperature is 110-150℃, and the hot pressing time is 1-5 minutes.

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