Gas-liquid two-channel microporous layer, preparation method and application thereof

Abstract

This invention discloses a gas-liquid dual-channel microporous layer, its preparation method, and its application, comprising the following steps: Step S1, zinc acetate is dissolved in methanol solution and dispersed to obtain solution A, 2-methylimidazole, hexadecyltrimethylammonium bromide, and sodium laurate are sequentially dissolved in methanol solution and dispersed to obtain solution B; Step S2, solution A is added to solution B, and after stirring, the solvent is removed to obtain a precipitate. The precipitate is vacuum dried to obtain a precursor p-ZIF-8, and the precursor p-ZIF-8 is subjected to high-temperature heat treatment to obtain porous carbon material p-ZIF-8-C; Step S3, the porous carbon material p-ZIF-8-C, a hydrophobic agent, and a solvent are mixed, dispersed, and prepared into a slurry. The slurry is coated onto a carbon fiber substrate in multiple applications. After coating, the solvent is removed by drying, and after calcination, a gas-liquid dual-channel microporous layer with a cracked surface is obtained. This invention improves the water management and gas transport capabilities inside the membrane electrode by precisely controlling the pore size of the carbon material and achieving adjustable microporous layer cracks, thereby enhancing the performance of the fuel cell.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, specifically to a gas-liquid dual-channel microporous layer, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) have shown broad application prospects in portable power sources, transportation, and stationary power stations due to their high energy conversion efficiency and environmental friendliness. The membrane electrode assembly (MEA), as the core component of a PEMFC, directly determines the battery's output power and stability. The gas diffusion layer (GDL), a key component of the MEA, is located between the catalyst layer and the bipolar plate channels, undertaking multiple functions including uniform diffusion of reactant gases, effective removal of product water, electron conduction, and heat management. The microporous layer (MPL), as the core functional layer of the gas diffusion layer, is typically formed by coating a carbon paper substrate with a mixture of conductive carbon materials (such as carbon black) and hydrophobic agents (such as polytetrafluoroethylene, PTFE). Its microstructure has a decisive influence on the gas-liquid transport balance inside the battery.

[0003] However, traditional methods for preparing microporous layers have significant limitations. First, the carbon materials used (such as acetylene black and carbon black) have a single and uncontrollable pore size distribution, making it difficult to simultaneously optimize the rapid diffusion of reactant gases (such as oxygen) and the efficient drainage of liquid water. Under high current density conditions, the large amount of liquid water generated by the catalyst layer can easily clog the narrow channels of the microporous layer, hindering gas transport to the catalyst layer, leading to severe concentration polarization and causing a "flooding" phenomenon, thus limiting the peak power density and operational stability of the battery. Second, existing technologies often introduce crack structures into the microporous layer to improve drainage capacity, but the control of cracks largely depends on adjusting the binder content or coating process parameters. This often changes the crack structure while also affecting the intrinsic hydrophilicity and hydrophobicity of the microporous layer, making it difficult to synergistically optimize gas-liquid management capabilities. For example, increasing the binder content may enhance structural strength but sacrifice some porosity and hydrophobicity, while simple adjustments to the drying process cannot achieve precise and independent control of crack width, density, and connectivity. Summary of the Invention

[0004] The purpose of this invention is to provide a new method for preparing a microporous layer, which can achieve precise control of the intrinsic pore size of carbon materials without changing the intrinsic hydrophobicity of the materials, and independently and controllably construct a macroscopic crack structure that is conducive to gas-liquid two-phase transport. This enables the construction of a dual-scale channel from microscopic pores to macroscopic cracks, fundamentally improving the gas mass transfer and liquid water management capabilities of the gas diffusion layer, and improving the mass transfer capability of fuel cells.

[0005] To achieve the above objectives, the present invention provides a method for preparing a gas-liquid dual-channel microporous layer, comprising the following steps: Step S1: Dissolve zinc acetate in methanol solution to obtain solution A; dissolve 2-methylimidazole, hexadecyltrimethylammonium bromide and sodium laurylate in methanol solution in sequence to obtain solution B. Step S2: Add solution A to solution B, stir, remove solvent to obtain precipitate, vacuum dry the precipitate to obtain precursor p-ZIF-8, subject precursor p-ZIF-8 to high temperature heat treatment to obtain porous carbon material p-ZIF-8-C. Step S3: The porous carbon material p-ZIF-8-C, hydrophobic agent and solvent are mixed and dispersed to form a slurry. The slurry is coated onto the carbon fiber substrate in multiple layers. After coating, the solvent is removed by drying. After calcination, a gas-liquid dual-channel microporous layer with a cracked surface is obtained.

[0006] Optionally, in step S1, the mass-to-volume ratio of zinc acetate to methanol solution is 1 g: (10~50) mL; in step S2, the mass-to-volume ratio of 2-methylimidazole to methanol solution is (1~6) g: (10~100) mL; and the mass ratio of hexadecyltrimethylammonium bromide to sodium laurylate is 1:2~2:1.

[0007] Optionally, in step S1, the dispersion method includes any one or more of magnetic stirring, ultrasonic dispersion, and high-pressure homogenization; the dispersion time is 10 min to 30 min.

[0008] Optionally, in step S2, after removing the solvent to obtain the precipitate, the precipitate is washed with an organic solvent, wherein the organic solvent includes any one of methanol, ethanol, propanol, and isopropanol.

[0009] Optionally, in step S2, the high-temperature heat treatment procedure is as follows: the temperature is increased to 900℃~1000℃ at a heating rate of 5~10℃ / min, and then kept at a constant temperature in a nitrogen or argon atmosphere for 2h~3h.

[0010] Optionally, in step S3, the hydrophobic agent is a nonionic hydrophobic agent, and the solvent includes any one or more of water, ethanol, and isopropanol.

[0011] Optionally, in step S3, the mass ratio of the porous carbon material p-ZIF-8-C to the hydrophobic agent is (5~20):1, and the mass-volume ratio of the porous carbon material p-ZIF-8-C to the solvent is 1g:(10~50)mL.

[0012] Optionally, in step S3, the calcination process is as follows: under an air atmosphere, the temperature is increased to 300℃~400℃ at a heating rate of 5~10℃ / min, and held at a constant temperature for 6h~10h.

[0013] The present invention also provides a gas-liquid dual-channel microporous layer, wherein the gas-liquid dual-channel microporous layer is prepared by any one of the preparation methods described above.

[0014] The present invention also provides an application of a gas-liquid dual-channel microporous layer in a fuel cell membrane electrode.

[0015] Compared to the prior art, the beneficial effects of the present invention include at least the following: (1) By adjusting the ratio of hexadecyltrimethylammonium bromide and sodium laurylate, the present invention can effectively guide the growth morphology of the precursor. After high-temperature carbonization, the pore size of the porous carbon material can be continuously and precisely controlled in the range of nanometers to submicrometers, which significantly improves the diffusion and transport efficiency of the reactant gas from the material source. (2) By controlling the number of coatings and selecting rapid heating and drying, the present invention can actively induce the formation of a uniform and interconnected crack network inside and on the surface of the microporous layer without changing the slurry formulation. These crack networks serve as macroscopic channels for the rapid discharge of liquid water. Combined with the micro-nano channels of the p-ZIF-8-C material itself (serving as gas transport channels), they form a highly efficient "gas-liquid dual-channel" structure, which fundamentally solves the problem that traditional single-channel structures cannot take into account both gas and liquid bidirectional transport. (3) Through the synergistic effect of pore size control and crack control, the prepared gas diffusion layer has both excellent gas mass transfer capability and liquid water management capability. When applied to hydrogen-oxygen fuel cells, it can effectively alleviate the water flooding problem under high current density, reduce concentration polarization, and significantly improve the output performance and operation stability of the battery under high load. Attached Figure Description

[0016] Figure 1 The images show SEM characterization images of the porous carbon material p-ZIF-8-C prepared in Examples 1-4 of the present invention; wherein, a is the porous carbon material p-ZIF-8-C-1 of Example 1; b is the porous carbon material p-ZIF-8-C-2 of Example 2; c is the porous carbon material p-ZIF-8-C-3 of Example 3; and d is the porous carbon material p-ZIF-8-C-4 of Example 4.

[0017] Figure 2 The images show the surface morphology of the gas-liquid dual-channel microporous layers prepared in Examples 1 and 5 of the present invention; a is the gas-liquid dual-channel microporous layer of Example 1; b is the gas-liquid dual-channel microporous layer of Example 5.

[0018] Figure 3 The images show high-resolution morphology of the gas-liquid dual-channel microporous layer at different magnifications in Embodiment 1 of the present invention.

[0019] Figure 4Performance test diagrams of the gas-liquid dual-channel microporous layers prepared in Examples 1-5 of the present invention and the microporous layers prepared in the comparative examples when used in low-temperature proton exchange membrane fuel cells. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] This invention provides a method for preparing a gas-liquid dual-channel microporous layer, comprising the following steps: Step S1: Dissolve zinc acetate in methanol solution to obtain solution A, and dissolve 2-methylimidazole, hexadecyltrimethylammonium bromide and sodium laurylate in methanol solution in sequence to obtain solution B.

[0022] Step S2: Add solution A to solution B, stir, remove solvent to obtain precipitate, vacuum dry the precipitate to obtain precursor p-ZIF-8, subject precursor p-ZIF-8 to high-temperature heat treatment to obtain porous carbon material p-ZIF-8-C; wherein, the pore size of p-ZIF-8-C is controlled by adjusting the feeding ratio of hexadecyltrimethylammonium bromide and sodium laurylate.

[0023] Step S3: Mix the porous carbon material p-ZIF-8-C, hydrophobic agent and solvent, disperse and prepare a slurry. Coat the slurry onto the carbon fiber substrate multiple times. After each coating, remove the solvent by rapid drying to preliminarily shape the microporous layer. Finally, calcine the coated carbon fiber substrate to obtain a gas-liquid dual-channel microporous layer with a cracked surface.

[0024] In some embodiments, in step S1, the mass-to-volume ratio of zinc acetate to methanol solution is 1 g: (10~50) mL; in step S2, the mass-to-volume ratio of 2-methylimidazole to methanol solution is (1~6) g: (10~100) mL; and the mass ratio of hexadecyltrimethylammonium bromide to sodium laurylate is 1:2~2:1.

[0025] In some embodiments, in step S1, the dispersion method includes any one or more of magnetic stirring, ultrasonic dispersion, and high-pressure homogenization; the dispersion time is 10 min to 30 min.

[0026] In some embodiments, in step S2, after removing the solvent to obtain a precipitate, the precipitate is washed with an organic solvent, wherein the organic solvent includes any one of methanol, ethanol, propanol, and isopropanol.

[0027] In some embodiments, the high-temperature heat treatment procedure in step S2 is as follows: the temperature is increased to 900℃~1000℃ at a heating rate of 5~10℃ / min, and then kept at a constant temperature in a nitrogen or argon atmosphere for 2h~3h.

[0028] In some embodiments, in step S3, the hydrophobic agent is a nonionic hydrophobic agent (e.g., PTFE, PFA, etc.), and the solvent includes any one or more of water, ethanol, and isopropanol.

[0029] In some embodiments, in step S3, the mass ratio of the porous carbon material p-ZIF-8-C to the hydrophobic agent is (5~20):1, and the mass-volume ratio of the porous carbon material p-ZIF-8-C to the solvent is 1g:(10~50)mL.

[0030] In some embodiments, the calcination process in step S3 is as follows: under an air atmosphere, the temperature is increased to 300°C to 400°C at a heating rate of 5 to 10°C / min, and then held at a constant temperature for 6 to 10 hours.

[0031] The gas-liquid dual-channel microporous layer prepared by this invention can be used as the gas diffusion layer of the anode and cathode of a fuel cell, and its catalytic activity can be evaluated by polarization curves.

[0032] Example 1 1) Pore size adjustment of carbon materials: 2g of zinc acetate was dissolved in 100mL of methanol solution and stirred for 10min to obtain solution A; 6.6g of 2-methylimidazole, 1.8g of hexadecyltrimethylammonium bromide and 0.9g of sodium laurylate were dissolved in 100mL of methanol solution and dispersed to obtain solution B; solution A was slowly added to solution B which was stirred rapidly. After stirring for a certain period of time, a white precipitate was obtained by removing the solvent and washed three times with methanol solution; the white precipitate was vacuum dried (overnight at 80℃) to obtain precursor p-ZIF-8. Precursor p-ZIF-8 was heat-treated at 900℃ (heating rate of 10℃ / min) for 2-3h to obtain p-ZIF-8-C-1 with a particle size of about 53-75 nm.

[0033] 2) Controllable preparation of cracked microporous layer: 1g p-ZIF-8-C-1, 0.2g PTFE and 50mL anhydrous ethanol were mixed to form a slurry, which was then dispersed and coated onto carbon fiber in three separate applications. After each coating, the carbon fiber of the microporous layer was freeze-dried (cold-drying temperature of -70℃ and pressure of 50Pa) to evaporate the solvent. After being kept at 300℃ for 6 hours in an air atmosphere, a gas-liquid dual-channel microporous layer (MPL-1) with a cracked surface structure was obtained. Figure 3 This is a high-resolution image of the gas-liquid dual-channel microporous layer in Example 1.

[0034] Example 2 Referring to the method described in Example 1, with the mass of hexadecyltrimethylammonium bromide remaining unchanged, the ratio of hexadecyltrimethylammonium bromide to sodium laurylate was adjusted to 1:1, and the remaining reaction conditions were the same as in Example 1, to prepare p-ZIF-8-C-2 with a particle size of approximately 205-260 nm. The gas-liquid dual-channel microporous layer was designated as MPL-2.

[0035] Example 3 Following the method described in Example 1, with the mass of hexadecyltrimethylammonium bromide remaining unchanged, the ratio of hexadecyltrimethylammonium bromide to sodium laurylate was adjusted to 1:1.5, and the remaining reaction conditions were the same as in Example 1, to prepare p-ZIF-8-C-3 with a particle size of approximately 620-740 nm. The gas-liquid dual-channel microporous layer was designated as MPL-3.

[0036] Example 4 Following the method described in Example 1, with the mass of hexadecyltrimethylammonium bromide remaining unchanged, the ratio of hexadecyltrimethylammonium bromide to sodium laurylate was adjusted to 1:2, and the remaining reaction conditions were the same as in Example 1, to prepare p-ZIF-8-C-4 with a particle size of approximately 1.5-1.65 μm. The gas-liquid dual-channel microporous layer was designated as MPL-4.

[0037] Example 5 Referring to the method described in Example 1, the freeze-drying was replaced with rapid heating drying (heating rate of 100℃ / min, temperature of 300℃), and the remaining reaction conditions were the same as in Example 1. p-ZIF-8-C-1 was prepared, and the gas-liquid dual-channel microporous layer was designated as MPL-5.

[0038] Comparative Example 1 Instead of using p-ZIF-8-C carbon material, EC-300J was used as the carbon material, and the remaining reaction conditions were the same as in Example 1. The microporous layer was designated as MPL-6.

[0039] like Figure 1 As shown, the particle size of p-ZIF-8-C in Examples 1-4 is different, such as... Figure 2 As shown, the surface morphology of the gas-liquid dual-channel microporous layer in Examples 1 and 5 is different.

[0040] The MPL-1-MPL-6 prepared in Examples 1-5 and Comparative Example 1 were used as cathode gas diffusion layers and assembled into fuel cell single cells for testing. The performance of a 2cm*2cm fuel cell single cell was tested under conditions where the anode was hydrogen and the cathode was oxygen, to characterize the performance of Examples 1-4 and Comparative Example 1 in a real hydrogen-oxygen fuel cell operating environment. The cathode was prepared by ultrasonic spraying of a 50% Pt / C catalyst and the anode by a 20% Pt / C nanocatalyst slurry. The platinum loadings of the anode and cathode were 0.2 and 0.3 mg Pt / cm, respectively. 2The battery temperature is 70°C, and the back pressure on both the anode and cathode sides is 100 kPa.

[0041] As shown in Table 1 and Figure 4 As shown, the samples from Examples 1-5 and Comparative Example 1 were at 0.8 A / cm 2 The voltages were 0.789V, 0.793V, 0.799V, 0.776V, 0.776V, and 0.726V, respectively, indicating that MPL-1 to MPL-5 all exhibited higher voltages than the traditional carbon black microporous layer MPL-6. This demonstrates the improved gas mass transfer effect of tunable pore size carbon materials, and shows that a suitable p-ZIF-8-C particle size is beneficial to improving the performance of hydrogen-oxygen fuel cells at high efficiency. The peak power densities of the samples in Examples 1-5 and Comparative Example 1 were 1.81 W / cm³. 2 1.73 W / cm 2 1.79 W / cm 2 1.71 W / cm 2 1.91 W / cm 2 1.49 W / cm 2 Larger cracks under rapid heating help improve the peak power density of hydrogen-oxygen fuel cells, and larger cracks promote the discharge of liquid water, thereby releasing greater performance potential at high current densities.

[0042] Table 1. Performance test data of the gas-liquid dual-channel microporous layers of Examples 1-5 and the microporous layer of Comparative Example 1 when applied to low-temperature proton exchange membrane fuel cells. In summary, the preparation method of the gas-liquid dual-channel microporous layer of the present invention includes the following steps: Step S1, zinc acetate is dissolved in methanol solution and dispersed to obtain solution A; 2-methylimidazole, hexadecyltrimethylammonium bromide, and sodium laurate are sequentially dissolved in methanol solution and dispersed to obtain solution B; Step S2, solution A is added to solution B, and after stirring, the solvent is removed to obtain a precipitate. The precipitate is vacuum dried to obtain precursor p-ZIF-8. The precursor p-ZIF-8 is subjected to high-temperature heat treatment to obtain porous carbon material p-ZIF-8-C; Step S3, the porous carbon material p-ZIF-8-C, a hydrophobic agent, and a solvent are mixed, dispersed, and prepared into a slurry. The slurry is coated onto a carbon fiber substrate in multiple applications. After coating, the solvent is removed by drying, and after calcination, a gas-liquid dual-channel microporous layer with a cracked surface structure is obtained. The present invention improves the water management and gas transport capacity inside the membrane electrode by precisely controlling the pore size of the carbon material and achieving tunable microporous layer cracks, thereby improving the performance of the fuel cell.

[0043] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a gas-liquid dual-channel microporous layer, characterized in that, Includes the following steps: Step S1: Dissolve zinc acetate in methanol solution to obtain solution A; dissolve 2-methylimidazole, hexadecyltrimethylammonium bromide and sodium laurylate in methanol solution in sequence to obtain solution B. Step S2: Add solution A to solution B, stir, remove solvent to obtain precipitate, vacuum dry the precipitate to obtain precursor p-ZIF-8, subject precursor p-ZIF-8 to high temperature heat treatment to obtain porous carbon material p-ZIF-8-C. Step S3: The porous carbon material p-ZIF-8-C, hydrophobic agent and solvent are mixed and dispersed to form a slurry. The slurry is coated onto the carbon fiber substrate in multiple layers. After coating, the solvent is removed by drying. After calcination, a gas-liquid dual-channel microporous layer with a cracked surface is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of zinc acetate to methanol solution is 1 g: (10~50) mL; in step S2, the mass-to-volume ratio of 2-methylimidazole to methanol solution is (1~6) g: (10~100) mL; and the mass ratio of hexadecyltrimethylammonium bromide to sodium laurylate is 1:2~2:

1.

3. The preparation method according to claim 1, characterized in that, In step S1, the dispersion method includes any one or more of magnetic stirring, ultrasonic dispersion, and high-pressure homogenization; the dispersion time is 10 min to 30 min.

4. The preparation method according to claim 1, characterized in that, In step S2, after removing the solvent to obtain the precipitate, the precipitate is washed with an organic solvent, wherein the organic solvent includes any one of methanol, ethanol, propanol, and isopropanol.

5. The preparation method according to claim 1, characterized in that, In step S2, the high-temperature heat treatment procedure is as follows: the temperature is increased to 900℃~1000℃ at a heating rate of 5~10℃ / min, and then kept at a constant temperature in a nitrogen or argon atmosphere for 2h~3h.

6. The preparation method according to claim 1, characterized in that, In step S3, the hydrophobic agent is a nonionic hydrophobic agent, and the solvent includes any one or more of water, ethanol, and isopropanol.

7. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of the porous carbon material p-ZIF-8-C to the hydrophobic agent is (5~20):1, and the mass-volume ratio of the porous carbon material p-ZIF-8-C to the solvent is 1g:(10~50)mL.

8. The preparation method according to claim 1, characterized in that, In step S3, the calcination process is as follows: under an air atmosphere, the temperature is increased to 300℃~400℃ at a heating rate of 5~10℃ / min, and then kept at a constant temperature for 6h~10h.

9. A gas-liquid dual-channel microporous layer, characterized in that, The gas-liquid dual-channel microporous layer is prepared by the preparation method described in any one of claims 1 to 8.

10. An application of the gas-liquid dual-channel microporous layer as described in claim 9, characterized in that, Application of the gas-liquid dual-channel microporous layer in fuel cell membrane electrode assembly.

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