Cathode catalyst layer of a fuel cell and fuel cell

Abstract

The application discloses a cathode catalytic layer of a fuel cell and the fuel cell. First, a covalent organic polymer TF-COF is prepared, which has regular vertical nanochannels and can provide a fast, low-resistance and directional transmission channel for oxygen molecules; the TF-COF has fluorination functional sites, and the F atom has strong electronegativity, so that the enrichment capacity of oxygen can be enhanced through electrophilic adsorption; meanwhile, the TF-COF has stable structure, low density and strong adjustability, and compared with traditional polymers, the COF is composed of light elements, has stronger structural stability and gas affinity, and is suitable for complex working conditions. The covalent organic polymer is doped into a traditional Pt / C catalytic layer, and only 2 mg to 4 cm 2 of the covalent organic polymer is needed to be added to the traditional Pt / C catalytic layer, so that the Pt / C catalytic layer has a Pt loading of 0.05 mgPt cm ‑2 , and in a hydrogen-air test environment, the peak power density of the Pt / C catalytic layer reaches 0.78 W cm ‑2 , which is increased by 34% compared with a control sample without the fluorinated COF.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a cathode catalyst layer and a fuel cell. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are highly efficient, zero-emission clean energy conversion devices widely used in portable power supplies, automotive power systems, ships, aerospace, and stationary power generation. The core component of a fuel cell is the membrane electrode assembly, which mainly consists of three parts: the cathode catalyst layer (CCL), the anode catalyst layer, and the proton exchange membrane. The CCL plays a crucial role in the operation of the fuel cell.

[0003] The cathode catalyst layer is generally composed of a noble metal catalyst (such as Pt / C), an ionomer (such as Nafion), and a gas diffusion layer. Its basic function is to maximize the gas-liquid-solid three-phase interface while ensuring the effective transport of electrons, protons, and reactant gases (oxygen), thereby accelerating the kinetics of the oxygen reduction reaction (ORR). Currently, fuel cell applications are limited by cost; to reduce costs, the amount of platinum used needs to be reduced. However, the performance of PEMFCs is limited by low platinum loading (≤ 0.1 mg). Pt cm −2 The performance of the cathode catalyst layer deteriorates sharply, and its dependence on oxygen mass transfer efficiency increases further. Cathode catalyst layers generally face the problem of high oxygen transport resistance. Poor porous structure, uneven distribution of ionomers, or excessive coverage of the catalyst inside the catalyst layer can severely hinder the effective transfer of oxygen to the catalytic active sites. To address the aforementioned issues, existing research has attempted to improve the oxygen transport capacity of the catalyst layer by introducing highly oxygen-permeable ionomer materials. For example, patent CN119954991A, "A Highly Oxygen-Permeable Ionomer with Large Steric Hindering Groups, Its Preparation Method and Application," proposes using fluorinated ionomers with large steric hindrance groups to enhance oxygen dissolution and diffusion performance. However, these highly oxygen-permeable ionomer solutions have the following drawbacks: 1. Complex synthesis: The introduction of functional groups into ionomers is complicated, and structural control is difficult, which is not conducive to mass production. 2. Material entanglement affects drainage: Flexible fluorinated chains are prone to entanglement and intertwining, which is not conducive to water drainage and can lead to local flooding problems; 3. Non-directional mass transfer path: Currently, most porous additives are non-structured channels, lacking through-guided pathways, requiring oxygen to diffuse in a tortuous manner, resulting in low efficiency.

[0004] Therefore, developing a novel material with a regular structure, oriented channels, and oxyfluorine-loving functional sites to improve the gas transport efficiency of the catalyst layer and the flux of the three-phase reaction zone has become a key requirement for solving the bottleneck problem of PEMFC. Summary of the Invention

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the object of the present invention is to overcome the shortcomings of the prior art and provide a cathode catalyst layer for a fuel cell.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a slurry is prepared by mixing Pt / C catalyst, Nafion ionomer, covalent organic polymer with structural formula (I), isopropanol and water, and then ultrasonically spraying the slurry. The amount of the covalent organic polymer with structural formula (I) relative to the Pt / C catalyst is 18wt%~22wt%. Formula (I).

[0008] Another object of the present invention is to provide a method for preparing a cathode catalyst layer for a fuel cell.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, Pt / C catalyst, Nafion ionomer, covalent organic polymer with the structural formula shown in formula (I), isopropanol and water are ultrasonically mixed in an ice bath to form a homogeneous catalyst slurry. The amount of the covalent organic polymer with the structural formula shown in formula (I) in the catalyst slurry is 18wt%~22wt% compared to the Pt / C catalyst; The contents of other components in the catalyst slurry are all conventional amounts used in the field and are not specifically limited.

[0010] The catalyst slurry is sprayed onto carbon paper with a microporous layer to form a catalyst layer, which serves as an electrode. The platinum loading of the catalyst layer is 0.03~0.1 mg cm⁻¹. -2 .

[0011] In a preferred embodiment of the method for preparing the cathode catalyst layer of a fuel cell according to the present invention, the method for preparing the covalent organic polymer is as follows: 40–50 mg of 2,4,6-amino-1,3,5-triazine, 2–4 mL of 1,4-dioxane, and 0.1–1 mL of 3M acetic acid were mixed and sonicated for 10–30 min to obtain a uniform dispersion. The dispersion was rapidly frozen at 77 K in liquid nitrogen and degassed through three freeze-pump-thaw cycles. After degassing, the mixture was sealed and heated. The resulting yellow precipitate was collected by centrifugation and washed with N,N-dimethylformamide and tetrahydrofuran. Finally, it was purified in a Soxhlet extractor with THF as solvent for 12-24 h and vacuum dried at 70-90 °C for 6-12 h to obtain a covalent organic polymer.

[0012] In a preferred embodiment of the method for preparing the cathode catalyst layer of a fuel cell according to the present invention, the temperature of the degassing and sealing heating is 115~125℃, and the time is 60~84 h.

[0013] Another object of the present invention is to provide a fuel cell in which the cathode utilizes the aforementioned cathode catalyst layer.

[0014] Another object of the present invention is to provide a method for preparing a fuel cell.

[0015] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, A gas diffusion electrode with a cathode catalyst layer and a gas diffusion electrode with an anode catalyst layer are placed on both sides of a proton exchange membrane, and then hot-pressed to obtain a membrane electrode. The membrane electrode assembly is performed by placing the membrane electrode on the graphite bipolar plate using PTFE pads, ensuring uniform force on the clamps, thus obtaining the fuel cell.

[0016] In a preferred embodiment of the fuel cell preparation method of the present invention, the hot pressing treatment is performed at a temperature of 110~130 ℃ for 5~15 min and at a pressure of 0.8~1.2 MPa.

[0017] Beneficial effects of this invention: This invention first prepares a covalent organic polymer TF-COF, which has regular vertical nanopores that can provide a fast and low-resistance directional transport channel for oxygen molecules; it has fluorinated functional sites, and due to the strong electronegativity of the F atom, it can enhance the oxygen enrichment capacity through electrophilic adsorption; at the same time, it has a stable structure, low density, and strong tunability. Compared with traditional polymers, COF is composed of light elements, has stronger structural stability and gas affinity, and is suitable for complex working conditions.

[0018] Doping this covalent organic polymer into a conventional Pt / C catalyst layer requires only 2 mg to 4 cm⁻¹ of additive. 2 Adding 20 wt% of the platinum-carbon catalyst to the membrane electrode can achieve a concentration of 0.05 mg Pt cm⁻¹. -2 Under load conditions, a peak power density of 0.78 W / cm² was achieved in a hydrogen-air testing environment. -2 Compared to the control sample without added fluorinated COF, it improved by 34%. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The infrared spectra of TTA, TAPT, and TF-COF in Embodiment 1 of the present invention are shown.

[0021] Figure 2 This is the XRD pattern of TF-COF in Embodiment 1 of the present invention.

[0022] Figure 3 The figures show the performance of the Pt / C@TF-COF-Nafion fuel cell in Example 1 and the Pt / C@Nafion fuel cell in Comparative Example 1 of this invention.

[0023] Figure 4 This is a diagram showing the oxygen transport resistance of Pt / C@TF-COF-Nafion in Example 1 and Pt / C@Nafion in Comparative Example 1.

[0024] Figure 5 The ORR performance diagrams of the catalyst layers prepared in Examples 1 to 3 of this invention are shown.

[0025] Figure 6 The oxygen absorption of TF-COF prepared in Example 1 and HCOF prepared in Comparative Example 2 are shown.

[0026] Figure 7 This is a comparison chart of the fuel cell performance of Pt / C@TF-COF-Nafion in Example 1, Pt / C@HCOF-Nafion in Comparative Example 2, and Pt / C@TF-HCOF-Nafion in Comparative Example 3. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] Unless otherwise specified, all raw materials used in this invention are commercially available in the art. In particular, the Pt / C catalyst used in the specific embodiment is TANAKA TKK 50% platinum-carbon catalyst from Japan, product model TEC10EA50, and the Nafion ionomer is DuPont 20% Nafion ionomer from the United States, product model D2020.

[0031] The test method for fuel cell performance in this invention refers to the national standard GB / T 20042.5-2024: Example 1: This example provides a cathode catalyst layer for a fuel cell and a method for preparing the fuel cell, specifically: Preparation of S1 covalent organic polymers: Add 2,4,6-amino-1,3,5-triazine (TTA, 48 mg, 0.45 mmol), 2,3,5,6-tetrafluoro-terephthalaldehyde (TFTA, 61 mg, 0.3 mmol), 3 mL of 1,4-dioxane, and 0.6 mL of 3 mol / L precipitate to a Schlenk tube. −1 Acetic acid was added, and the mixture was sonicated for 10 min to obtain a uniform dispersion. The Schlenk tube was then rapidly frozen at 77 K in liquid nitrogen and degassed by three freeze-pump-thaw cycles. After degassed, the Schlenk tube was sealed and heated at 120 °C for 72 h. The resulting yellow precipitate was collected by centrifugation and washed with N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). Finally, it was purified in a Soxhlet extractor with THF as solvent for 24 h and vacuum dried at 80 °C for 12 h to obtain the covalent organic polymer TF-COF, with the structural formula shown in formula (I). Formula (I); The infrared spectra of the monomers used and the synthesized covalent organic polymer TF-COF are as follows: Figure 1 As shown, Figure 1 It can be seen that it is 1706 cm. −1 The absorption peak at C=O and 3325 cm⁻¹ −1 3214 cm −1 The disappearance of the -NH2 absorption peak indicates that the reaction proceeded successfully. Figure 2The image shows the XRD pattern of TF-COF. The figure shows that the COF has good crystallinity, which proves that the synthesized COF has a regular AA stacked structure and an ordered pore structure.

[0032] The covalent organic polymer obtained in this step has regular vertical nanopores, which can provide a fast and low-resistance directional transport channel for oxygen molecules; it has fluorinated functional sites, and due to the strong electronegativity of the F atom, it can enhance the oxygen enrichment capacity through electrophilic adsorption; at the same time, it has a stable structure, low density, and strong tunability: compared with traditional polymers, COF is composed of light elements, has stronger structural stability and gas affinity, and is suitable for complex working conditions.

[0033] Preparation of the cathode catalyst layer for S2 fuel cell: 50 mg of Pt / C catalyst, 30 μL of Nafion ionomer, 10 mg of the covalent organic polymer TF-COF obtained in step S1, 10 mL of isopropanol and 20 mL of water were ultrasonically mixed in an ice bath for 30 min to form a uniform catalyst slurry. The amount of the covalent organic polymer with the structural formula shown in formula (I) in the catalyst slurry is 20 wt% compared to the Pt / C catalyst. The catalyst slurry was ultrasonically sprayed in a 1.62 mL volume onto carbon paper (25 cm²) with a microporous layer. -2 A catalytic layer is formed on the platinum layer with a platinum loading as low as 0.05 mg cm⁻¹. -2 And serve as the cathode catalyst layer for fuel cells. Fabrication of S3 fuel cells: Carbon paper with a cathode catalyst layer and carbon paper with an anode catalyst layer were placed on both sides of the proton exchange membrane, respectively. The membrane electrode was obtained by hot pressing at 120 °C and 0.8 MPa for 5 min. The membrane electrode assembly is performed by placing it on a graphite bipolar plate using a PTFE pad, ensuring uniform force on the clamps, thus obtaining the fuel cell Pt / C@TF-COF-Nafion of this embodiment.

[0034] Comparative Example 1 differs from Example 1 in that the covalent organic polymer TF-COF prepared in Example 1 was not added to the cathode catalyst layer of the fuel cell. All other steps were the same as in Example 1. The catalyst layer, electrode and fuel cell of this comparative example were obtained and denoted as Pt / C@Nafion.

[0035] The performance of the fuel cells prepared in Comparative Example 1 and this comparative example is as follows: Figure 3 As shown, from Figure 3 It can be seen that using this fluorinated COF material to dope a traditional Pt / C catalyst layer requires only 10 mg to 25 cm⁻¹ of material. -2 In membrane electrodes, 0.05 mg can be used.Pt cm -2 Under load conditions, a peak power density of 0.78 Wcm³ was achieved in a hydrogen-air test environment. -2 Compared to the control sample without added fluorinated COF, it improved by 34%. Figure 4 The oxygen transport resistance of Pt / C@TF-COF-Nafion in Example 1 and Pt / C@Nafion in Comparative Example 1 is determined from... Figure 4 It can be seen that, compared with Pt / C@Nafion, Pt / C@TF-COF-Nafion exhibits a significant decrease in oxygen transport resistance.

[0036] Example 2 differs from Example 1 in that the amount of covalent organic polymer used in step S2 is adjusted. Specifically: 50 mg of commercial Pt / C catalyst, 30 μL of Nafion ionomer, 9 mg of covalent organic polymer TF-COF, 10 mL of isopropanol and 20 mL of water were ultrasonically mixed in an ice bath for 30 min to form a homogeneous catalyst slurry. The amount of the covalent organic polymer with the structural formula (I) in the catalyst slurry is 18 wt% compared to the amount of Pt / C catalyst. The remaining steps and processes are the same as in Example 1, resulting in the catalyst layer, electrode, and fuel cell of this example.

[0037] Example 3 differs from Example 1 in that the amount of covalent organic polymer used in step S2 is adjusted. Specifically: 50 mg of commercial Pt / C catalyst, 30 μL of Nafion ionomer, 11 mg of covalent organic polymer TF-COF, 10 mL of isopropanol and 20 mL of water were ultrasonically mixed in an ice bath for 30 min to form a homogeneous catalyst slurry. The amount of the covalent organic polymer with the structural formula shown in formula (I) in the catalyst slurry is 22 wt% compared to that of the Pt / C catalyst; The remaining steps and processes are the same as in Example 1, resulting in the catalyst layer, electrode, and fuel cell of this example.

[0038] The ORR performance of the catalyst layers prepared in Examples 2 and 3 was measured and compared with that of Example 1. The results are as follows: Figure 5 As shown, it can be seen that the ORR performance of Example 2 is slightly lower than that of Examples 1 and 3, which is comparable to that of Examples 1 and 3. This indicates that when the amount of covalent organic polymer TF-COF added is insufficient, the oxygen transport channels provided by the polymer are limited, thus limiting the increase in reactant concentration near the catalyst layer and resulting in limited performance improvement. Adding excessive TF-COF does not further increase the ORR performance.

[0039] Comparative Example 2 differs from Example 1 in that the covalent organic polymer TF-COF in the system is changed to HCOF. Specifically: Preparation of the covalent organic polymer HCOF: Add 2,4,6-amino-1,3,5-triazine (48 mg, 0.45 mmol), terephthalaldehyde (40 mg, 0.3 mmol), 3 mL of 1,4-dioxane, and 0.6 mL of 3M acetic acid to a Schlenk tube, and sonicate the mixture for 10 min to obtain a uniform dispersion. The Schlenk tube was then rapidly frozen at 77 K in liquid nitrogen and degassed through three freeze-pump-thaw cycles. After degassing, the Schlenk tube was sealed and heated at 120°C for 72 h. The resulting yellow precipitate was collected by centrifugation and washed with DMF and THF. Finally, it was purified in a Soxhlet extractor with THF as solvent for 24 h and vacuum dried at 80°C for 12 h to obtain the covalent organic polymer HCOF.

[0040] Comparing the oxygen absorption of the comparative covalent organic polymer HCOF with that of the covalent organic polymer TF-COF in Example 1, the results are as follows: Figure 6 As shown, although the covalent organic polymer HCOF obtained in this step has regular vertical nanopores, from Figure 6 It can be seen that, compared with TF-COF in Example 1, the oxygen absorption of HCOF is significantly reduced.

[0041] The remaining steps and processes were all the same as in Example 1, and the catalyst layer, electrode and fuel cell of this comparative example were obtained, denoted as Pt / C@HCOF-Nafion.

[0042] Comparative Example 3 differs from Example 1 in that the covalent organic polymer TF-COF in the system is changed to TF-HCOF. Specifically: Preparation of covalent organic polymer TF-HCOF: Add 2,4,6-amino-1,3,5-triazine (48 mg, 0.45 mmol), 2,5-difluoroterephthalaldehyde (51 mg, 0.3 mmol), 3 mL of 1,4-dioxane, and 0.6 mL of 3M acetic acid to a Schlenk tube, and sonicate the mixture for 10 min to obtain a uniform dispersion. The Schlenk tubes were then rapidly frozen at 77 K in liquid N2 and degassed through three freeze-pump-thaw cycles. After degassing, the Schlenk tube was sealed and heated at 120°C for 72 h. The resulting yellow precipitate was collected by centrifugation and washed with DMF and THF. Finally, it was purified in a Soxhlet extractor with THF as solvent for 24 h and vacuum dried at 80°C for 12 h to obtain the covalent organic polymer TF-HCOF of this comparative example.

[0043] The remaining steps and processes were all the same as in Example 1, and the catalyst layer, electrode and fuel cell of this comparative example were obtained, denoted as Pt / C@TF-HCOF-Nafion.

[0044] The performance of the fuel cells prepared in Comparative Examples 2 and 3 was measured and compared with that in Example 1. The results are as follows: Figure 7 As shown, the fuel cell performance of Pt / C@HCOF-Nafion and Pt / C@TF-HCOF-Nafion is significantly lower than that of Pt / C@TF-COF-Nafion in Example 1. Although HCOF in Comparative Example 2 has regular channels, it lacks fluorination functional sites, resulting in limited oxygen enrichment and low oxygen mass transfer efficiency. The partial fluorination sites of F-HCOF enhance oxygen affinity, but do not fully utilize the directional transport advantage of fluorination channels. Oxygen enrichment and directional diffusion are still inferior to the perfluorinated TF-COF prepared in Example 1 of this invention.

[0045] The TF-COF of this invention has both regular vertical nanopores that provide low-resistance directional transport channels for oxygen and fluorination sites that can enhance oxygen enrichment through electrophilic adsorption, thereby significantly improving the three-phase interface reaction efficiency and fuel cell power output. It can simultaneously take into account oxygen transport efficiency and oxygen enrichment capacity in the catalyst layer, thereby maximizing fuel cell performance under low platinum loading conditions.

[0046] In summary, this invention first prepared a covalent organic polymer TF-COF, which has regular vertical nanopores that can provide a fast and low-resistance directional transport channel for oxygen molecules; it has fluorinated functional sites, and due to the strong electronegativity of the F atom, it can enhance the oxygen enrichment capacity through electrophilic adsorption; at the same time, it has a stable structure, low density, and strong tunability. Compared with traditional polymers, COF is composed of light elements, has stronger structural stability and gas affinity, and is suitable for complex working conditions.

[0047] Doping this covalent organic polymer into a conventional Pt / C catalyst layer requires only 2 mg to 4 cm⁻¹ of additive. 2 Adding 20 wt% of the platinum-carbon catalyst to the membrane electrode can achieve a concentration of 0.05 mg Pt cm⁻¹. -2 Under load conditions, a peak power density of 0.78 W / cm² was achieved in a hydrogen-air testing environment. -2 Compared to the control sample without added fluorinated COF, it improved by 34%.

[0048] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A cathode catalyst layer for a fuel cell, characterized in that: The mixture is prepared by ultrasonic spraying of a slurry made from Pt / C catalyst, Nafion ionomer, a covalent organic polymer with the structural formula shown in formula (I), isopropanol, and water, wherein the amount of the covalent organic polymer with the structural formula shown in formula (I) is 18wt%~22wt% compared to the amount of Pt / C catalyst. Equation (I).

2. The method for preparing the cathode catalyst layer of a fuel cell according to claim 1, characterized in that: include, Pt / C catalyst, Nafion ionomer, covalent organic polymer with the structural formula shown in formula (I), isopropanol and water are ultrasonically mixed in an ice bath to form a homogeneous catalyst slurry. The amount of the covalent organic polymer with the structural formula shown in formula (I) in the catalyst slurry is 18wt%~22wt% compared to the Pt / C catalyst; The catalyst slurry is sprayed onto carbon paper with a microporous layer to form a catalyst layer, which serves as an electrode. The platinum loading of the catalyst layer is 0.03~0.1 mg cm⁻¹. -2 .

3. The method for preparing the cathode catalyst layer of a fuel cell as described in claim 2, characterized in that: The method for preparing the covalent organic polymer is as follows: 40–50 mg of 2,4,6-amino-1,3,5-triazine, 2–4 mL of 1,4-dioxane, and 0.1–1 mL of 3M acetic acid were mixed and sonicated for 10–30 min to obtain a uniform dispersion. The dispersion was rapidly frozen at 77 K in liquid nitrogen and degassed through three freeze-pump-thaw cycles. After degassing, the mixture was sealed and heated. The resulting yellow precipitate was collected by centrifugation and washed with N,N-dimethylformamide and tetrahydrofuran. Finally, it was purified in a Soxhlet extractor with THF as solvent for 12-24 h and vacuum dried at 70-90 °C for 6-12 h to obtain a covalent organic polymer.

4. A method for preparing a cathode catalyst layer for a fuel cell as described in claim 3, characterized in that: The temperature for the degassing followed by sealing and heating is 115~125℃, and the time is 60~84 h.

5. A fuel cell, characterized in that: The cathode of the fuel cell uses the cathode catalyst layer as described in claim 1.

6. The method for preparing a fuel cell as described in claim 4, characterized in that: include, A gas diffusion electrode with a cathode catalyst layer and a gas diffusion electrode with an anode catalyst layer are placed on both sides of a proton exchange membrane, and then subjected to hot pressing to obtain a membrane electrode. The membrane electrode assembly is performed by placing the membrane electrode on the graphite bipolar plate using PTFE pads, ensuring uniform force on the clamps, thus obtaining the fuel cell.

7. The method for preparing a fuel cell as described in claim 6, characterized in that: The hot pressing treatment is performed at a temperature of 110~130 ℃, for a time of 5~15 min, and at a pressure of 0.8~1.2 MPa.

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