A fuel cell CCM and its preparation method

Abstract

This invention discloses a fuel cell membrane electrode assembly (CCM) and its preparation method, belonging to the field of fuel cell membrane electrode assembly design and optimization methods. The fuel cell CCM includes a catalyst layer and a proton exchange membrane (PEM). The catalyst support in the catalyst layer has an average pore size ≥ 5 nm. When the thickness of the PEM is ≤ 15 μm, the average particle size of the catalyst layer slurry is 3.6–5.5 μm; when the thickness of the PEM is > 15 μm, the average particle size of the catalyst layer slurry is 1.5–3.5 μm. This invention, based on the pore size properties of the catalyst support and combined with the thickness of the PEM, adjusts the average particle size range of the slurry, effectively improving the performance of the membrane electrode assembly under high current density.

Description

Technical Field

[0001] This invention belongs to the field of design and optimization methods for fuel cell membrane electrode assemblies, specifically relating to a fuel cell CCM and its preparation method. Background Technology

[0002] The membrane electrode assembly (MEA) is the core component of a proton exchange membrane fuel cell (PEMFC), consisting of three parts: the catalyst layer (CL), the proton exchange membrane (PEM), and the gas diffusion layer (GDL). The combination of the catalyst layer (CL) and the proton exchange membrane (PEM) is called the catalyst coated membrane (CCM). As the most important component of the MEA, the CCM not only conducts protons but also serves as the site of electrochemical reactions, directly affecting the performance and durability of the membrane electrode. In recent years, most research has focused on optimizing the catalyst layer, primarily targeting the catalyst slurry. This includes adjusting the resin content in the slurry, adding dispersants such as PTFE and cetyltrimethylammonium bromide, and preparing novel catalysts. Most studies only analyze the impact of a single variable on performance, without considering material properties to match the optimal slurry formulation for the design and optimization of the CCM.

[0003] Zhang Jun of China Electronics Technology Group Corporation studied the effects of single variables (different dispersion solvents, different proton exchange membranes, etc.) on membrane electrode performance. However, he did not consider the influence of the pore structure and other characteristics of the catalyst support, or the effect of slurry particle size on the slurry dispersion effect. Summary of the Invention

[0004] The purpose of this invention is to provide a CCM and its preparation method that can effectively improve the performance of membrane electrode for catalysts with an average pore size ≥ 5 nm by changing the average particle size range of the slurry and matching a suitable proton exchange membrane.

[0005] Based on the pore structure properties of the catalyst and the thickness characteristics of the proton exchange membrane, this invention achieves optimal mass transfer conditions for the catalyst layer by adjusting the average particle size of the catalyst slurry, thereby effectively improving the performance of CCM at high current densities.

[0006] This invention provides a fuel cell CCM, comprising a catalyst layer and a proton exchange membrane, wherein the catalyst support in the catalyst layer has an average pore size ≥ 5 nm; when the thickness of the proton exchange membrane is ≤ 15 μm, the average particle size of the catalyst layer slurry is 3.6–5.5 μm; when the thickness of the proton exchange membrane is > 15 μm, the average particle size of the catalyst layer slurry is 1.5–3.5 μm.

[0007] This invention also provides a method for preparing a fuel cell CCM, comprising the following steps:

[0008] (1) When the thickness of the proton exchange membrane is ≤15μm:

[0009] A dispersion solvent was added to a carbon-supported noble metal catalyst with an average pore size ≥ 5 nm. After ultrasonic dispersion, an ionomer was added and stirred until homogeneous. By adjusting the ratio of water and organic solvent in the dispersion solvent, the average particle size of the slurry was controlled to be 3.6 μm to 5.5 μm. The slurry was then coated onto a proton exchange membrane with a thickness ≤ 15 μm to obtain the fuel cell CCM.

[0010] (2) When the thickness of the proton exchange membrane is >15μm:

[0011] A dispersion solvent was added to a carbon-supported noble metal catalyst with an average pore size ≥ 5 nm. After ultrasonic dispersion, an ionomer was added and stirred until homogeneous. By adjusting the ratio of water and organic solvent in the dispersion solvent, the average particle size of the slurry was controlled to be 1.5 μm to 3.5 μm. The slurry was then coated onto a proton exchange membrane with a thickness > 15 μm to obtain the fuel cell CCM.

[0012] Furthermore, in the above technical solution, the organic solvent includes one or a mixture of two or more of ethanol, dimethylacetamide, n-propanol, isopropanol, glycerol, and N-methylpyrrolidone; when the volume ratio of water to organic solvent in the dispersion solvent is 1 / 2 to 1 / 8:1 / 8, the average particle size of the slurry is 3.6 μm to 5.5 μm; when the volume ratio of aqueous phase to organic phase in the dispersion solvent is 1 / 8:1 / 2 to 1 / 8, the average particle size of the slurry is 1.5 μm to 3.5 μm.

[0013] Furthermore, in the above technical solution, the precious metal includes one or more of Pt, Co, Pd, etc.

[0014] Furthermore, in the above technical solution, the mass fraction of noble metal in the carbon-supported noble metal catalyst is 20%-80%.

[0015] Furthermore, in the above technical solution, the loading of noble metals in the catalyst layer of the fuel cell CCM is 0.01–0.3 mg / cm³. 2 .

[0016] Furthermore, in the above technical solution, the amount of the dispersing solvent added is 10-100g.

[0017] Furthermore, in the above technical solution, the mass ratio of the ionomer to the carrier is 0.4 to 1.3.

[0018] Furthermore, in the above technical solution, the slurry is coated on one or both sides of the proton exchange membrane, and the coating method includes ultrasonic spraying, slit coating or transfer printing.

[0019] Furthermore, in the above technical solution, the ionic polymer is a Nafion solution with a mass fraction of 1%-10%.

[0020] Beneficial effects of the invention

[0021] Most current research focuses on the optimization of catalyst layer slurry by selecting different dispersants, different proton exchange membranes, and different catalysts as single variables. However, CCM is a very complex system that can only exhibit better performance through the synergistic effect of multiple materials such as catalysts, dispersants, ionomers, and proton exchange membranes.

[0022] This invention effectively improves membrane electrode performance by adjusting the average particle size range of the slurry based on the pore size properties of the catalyst support and the thickness of the proton exchange membrane. Experiments have shown that:

[0023] For catalysts with an average pore size ≥ 5 nm on the support, optimal performance is achieved when using a proton exchange membrane with a thickness ≤ 15 μm and controlling the average particle size of the slurry within the range of 3.6–5.5 μm. This is because, due to the larger pore size of the support, the proton conduction of the catalyst layer is highly dependent on the ionomers. Using a thinner proton exchange membrane results in stronger water back diffusion and a drier cathode catalyst layer. In this case, the average particle size of the slurry is larger, indicating better dispersion of the ionomers in the slurry. The catalyst surface has more ionomer films, which enhance proton conduction and improve performance. Conversely, if a proton exchange membrane with a thickness > 15 μm is used, water back diffusion is slower, and there is more water in the cathode catalyst layer. In this case, if the slurry particle size is larger, the catalyst surface will be covered with more ionomer films. These ionomer films will absorb more water, generating greater mass transfer resistance, resulting in poorer performance. In this situation, the optimal performance is achieved when the average particle size of the slurry is between 1.5 and 3.5 μm.

[0024] This invention comprehensively considers the material properties of the catalyst and the thickness characteristics of the proton exchange membrane in the catalyst layer, and finds that the average particle size of the slurry can affect the mass transfer capacity of the catalyst layer. For catalysts with an average pore size ≥ 5 nm on the support, the electrode performance can be effectively improved by controlling the average particle size of the slurry for proton exchange membranes of different thicknesses. The method adopted in this invention does not introduce impurities into the system, is simple to operate, and has low cost. Attached Figure Description

[0025] Figure 1 This is a diagram of the CCM structure.

[0026] Figure 2 This represents the pore size distribution of the catalyst support.

[0027] Figure 3 Performance test graphs of the CCMs prepared in Examples 1-3 and Comparative Examples 1-3. Detailed Implementation

[0028] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0029] Example 1

[0030] (1) Weigh 3g of Pt / C catalyst (average pore size of support ≥5nm, noble metal content 50wt%) and add it to a beaker. Add a certain amount of dispersant, which is a mixture of water and n-propanol. Then add 20.6g of Nafion solution, stir for 10min, and then ultrasonically disperse it evenly. Adjust the amount of dispersant so that the volume ratio of water to organic solvent (n-propanol) in the dispersant is 2.2, and the average particle size of the slurry is 4.5μm. In this example, the amount of dispersant added is 98g.

[0031] (2) The above-mentioned mixed slurry was coated onto both sides of a proton exchange membrane with a thickness ≤15μm by ultrasonic spraying, with a total noble metal loading of 0.3mg / cm³. 2 .

[0032] Example 2

[0033] (1) Weigh 3g of Pt / C catalyst (average pore size of support ≥5nm, noble metal content 50wt%) and add it to a beaker. Add a certain amount of dispersant, which is a mixture of water and n-propanol. Then add 20.6g of ionomer solution, stir for 10min, and then ultrasonically disperse it evenly. Adjust the amount of dispersant so that the volume ratio of water to organic solvent (n-propanol) in the dispersant is 0.3, and the average particle size of the slurry is 3.3μm. In this embodiment, the amount of dispersant added is 98g.

[0034] (2) The above-mentioned mixed slurry was coated onto both sides of a proton exchange membrane with a thickness >15 μm by ultrasonic spraying, with a total noble metal loading of 0.3 mg / cm³. 2 .

[0035] Example 3

[0036] (1) Weigh 3g of PtCo / C catalyst (average pore size of support ≥5nm, noble metal content 50wt%) and add it to a beaker. Add a certain amount of dispersant, which is a mixture of water and N-methylpyrrolidone. Then add 20.6g of Nafion solution, stir for 10min, and then ultrasonically disperse it evenly. Adjust the amount of dispersant so that the volume ratio of water to organic phase (N-methylpyrrolidone) in the dispersant is 3.3, and the average particle size of the slurry is 4.8μm. In this example, the amount of dispersing solvent added is 98g.

[0037] (2) The above-mentioned mixed slurry was coated onto both sides of a proton exchange membrane with a thickness ≤15μm by ultrasonic spraying, with a total noble metal loading of 0.3mg / cm³. 2 .

[0038] Comparative Example 1

[0039] (1) Weigh 3g of Pt / C catalyst (average pore size of support ≥5nm, noble metal content 50wt%) and add it to a beaker. Add a certain amount of dispersant, which is a mixture of water and n-propanol. Then add 20.6g of Nafion solution, stir for 10min, and then ultrasonically disperse it evenly. Adjust the amount of dispersant so that the volume ratio of water to organic solvent (n-propanol) in the dispersant is 0.5, and the average particle size of the slurry is 2.9μm. In this example, the amount of dispersing solvent added is 98g.

[0040] (2) The above-mentioned mixed slurry was coated onto both sides of a proton exchange membrane with a thickness ≤15μm by ultrasonic spraying, with a total noble metal loading of 0.3mg / cm³. 2 .

[0041] Comparative Example 2

[0042] (1) Weigh 3g of Pt / C catalyst (average pore size of support ≥5nm, noble metal content 50wt%) and add it to a beaker. Add a certain amount of dispersant, which is a mixture of water and n-propanol. Then add 20.6g of Nafion solution, stir for 10min, and then ultrasonically disperse it evenly. Adjust the amount of dispersant so that the volume ratio of water to organic solvent (n-propanol) in the dispersant is 3, so that the average particle size of the slurry is 4.0μm. In this example, the amount of dispersing solvent added is 98g.

[0043] (2) The above-mentioned mixed slurry was coated onto both sides of a proton exchange membrane with a thickness >15 μm by ultrasonic spraying, with a total noble metal loading of 0.3 mg / cm³. 2 .

[0044] Comparative Example 3

[0045] (1) Weigh 3g of PtCo / C catalyst (average pore size of support ≥5nm, noble metal content 50wt%) and add it to a beaker. Add a certain amount of dispersant, which is a mixture of water and N-methylpyrrolidone. Then add 20.6g of Nafion solution, stir for 10min, and then ultrasonically disperse it evenly. Adjust the amount of dispersant so that the volume ratio of water to organic solvent (N-methylpyrrolidone) in the dispersant is 0.8, and the average particle size of the slurry is 2.3μm. In this example, the amount of dispersing solvent added is 98g.

[0046] (2) The above-mentioned mixed slurry was coated onto both sides of a proton exchange membrane with a thickness ≤15μm by ultrasonic spraying, with a total noble metal loading of 0.3mg / cm³. 2 .

[0047] The CCMs prepared in Examples 1-3 and Comparative Examples 1-3 were combined with a gas diffusion layer and a polyester frame to form a MEA via hot pressing. These were then assembled into a short stack, and polarization curve tests were performed. The test results are as follows: Figure 3 As shown in the figure, for catalysts with an average pore size ≥ 5 nm on the support, a slurry average particle size range of 3.6–5.5 μm is beneficial for performance improvement when matched with a thinner proton exchange membrane; while a slurry average particle size range of 1.5–3.5 μm is beneficial for performance improvement when matched with a thicker proton exchange membrane.

[0048] The above embodiments are merely illustrative and explanatory of the present invention and are not intended to limit the invention to the scope of the described embodiments. Furthermore, those skilled in the art will understand that the present invention is not limited to the above embodiments, and many more variations and modifications can be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention.

Claims

1. A fuel cell CCM, characterized by, The application relates to a catalyst carrier with an average pore diameter of greater than or equal to 5 nm and a proton exchange membrane, wherein the average particle size of the catalyst layer slurry is 3.6-5.5 mu m when the thickness of the proton exchange membrane is less than or equal to 15 mu m, and the average particle size of the catalyst layer slurry is 1.5-3.5 mu m when the thickness of the proton exchange membrane is greater than 15 mu m.

2. A method of making a fuel cell CCM, characterized by, The application relates to a method for preparing a catalyst carrier with an average pore diameter of greater than or equal to 5 nm and a proton exchange membrane, and comprises the following steps: (1) when the thickness of the proton exchange membrane is less than or equal to 15 mu m: carbon-supported noble metal catalyst with an average pore diameter of greater than or equal to 5 nm is added with a dispersion solvent, and then uniformly dispersed by ultrasonic dispersion; an ionic polymer is added and uniformly stirred; the average particle size of the slurry is controlled to be 3.6-5.5 mu m by adjusting the proportion of water and organic solvent in the dispersion solvent; the slurry is coated on the proton exchange membrane with a thickness of less than or equal to 15 mu m to obtain a fuel cell CCM; (2) when the thickness of the proton exchange membrane is greater than 15 mu m: carbon-supported noble metal catalyst with an average pore diameter of greater than or equal to 5 nm is added with a dispersion solvent, and then uniformly dispersed by ultrasonic dispersion; an ionic polymer is added and uniformly stirred; the average particle size of the slurry is controlled to be 1.5-3.5 mu m by adjusting the proportion of water and organic solvent in the dispersion solvent; the slurry is coated on the proton exchange membrane with a thickness of greater than 15 mu m to obtain a fuel cell CCM.

3. The preparation method according to claim 2, characterized in that, The organic solvent comprises one or more than two kinds of mixture of ethanol, dimethylacetamide, n-propanol, isopropanol, glycerol and N-methyl pyrrolidone; when the volume ratio of water and organic solvent in the dispersion solvent is 1 / 2-1 / 8:1 / 8, the average particle size of the slurry is 3.6-5.5 mu m; when the volume ratio of water and organic solvent in the dispersion solvent is 1 / 8:1 / 2-1 / 8, the average particle size of the slurry is 1.5-3.5 mu m.

4. The preparation method according to claim 2, characterized in that, The noble metal comprises one or more than two kinds of Pt, Co and Pd.

5. The preparation method according to claim 2, characterized in that, The mass fraction of the noble metal in the carbon-supported noble metal catalyst is 20%-80%.

6. The preparation method according to claim 2, characterized in that, The supported amount of noble metal in the catalytic layer of the fuel cell CCM is 0.01 to 0.3 mg / cm 2 .

7. The preparation method according to claim 2, characterized in that, The adding amount of the dispersion solvent is 10-100 g.

8. The preparation method according to claim 2, characterized in that, The mass ratio of the ionic polymer to the carrier is 0.4-1.

3.

9. The preparation method according to claim 2, characterized in that, The slurry is coated on one side or both sides of the proton exchange membrane, and the coating mode comprises ultrasonic spraying, slot coating or transfer printing.

10. The method of claim 2, wherein, The ionic polymer is a Nafion solution with a mass fraction of 1%-10%.

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