Design and application for constructing hierarchical porous catalyst layer of high-drainage porous membrane electrode based on micro-nano bubbles

Abstract

The invention relates to a method for preparing a hierarchical porous catalyst layer of a high-drainage porous membrane electrode based on micro-nano bubbles, which comprises the following steps of: generating oxygen bubbles under the catalysis of carbon-loaded platinum by taking hydrogen peroxide as a bubble source, and constructing the high-drainage porous membrane electrode by taking the micro-nano bubbles as a template; the specific method comprises the following steps: dissolving a carbon-supported platinum catalyst PtC and a Nafion solution in ethanol and water to obtain a solution, carrying out ultrasonic treatment on the solution, dropwise coating the solution on carbon paper at 80 DEG C, and dropwise adding a hydrogen peroxide solution in the coating process; and drying in a vacuum freeze drying box after air drying. According to the invention, the membrane electrode with high porosity is constructed, so that liquid water is effectively prevented from blocking pores, and the phenomenon of water logging in the battery is relieved. According to the preparation method, shrinkage and agglomeration of catalyst particles are avoided, and the hierarchical porous catalyst layer of the porous membrane electrode with high drainage performance is obtained. The invention also provides application of the porous membrane electrode in the field of fuel cells.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to the design and application of a hierarchical porous catalytic layer for constructing a highly drainable porous membrane electrode based on micro-nano bubbles. Background Technology

[0002] With rapid economic and cultural development, people's understanding of the natural environment is constantly deepening. It has been discovered that our past over-reliance on and uncontrolled extraction and use of oil has led to the rapid depletion of fossil fuels, resulting in severe environmental pollution and energy shortages. This has made finding clean and efficient alternative energy sources and developing new materials a crucial issue of common concern for governments and the general public worldwide. Proton exchange membrane fuel cells (PEMFCs) are a highly efficient and environmentally friendly energy conversion technology with the potential to address global energy and environmental challenges. Research indicates that hydrogen energy and hydrogen fuel cell technology hold promise for large-scale applications in automobiles, portable power generation, and stationary power stations. With the development of fuel cell technology, the membrane electrode assembly (MEA) in practical onboard PEMFC systems is generally becoming thinner. While this improves water transport performance, it also increases the risk of flooding, generates more water, and operates at higher pressures. Gaseous water is more prone to liquefaction, clogging the gas diffusion layer (GDL) and flow channels, hindering mass transfer of reactant gases, causing insufficient gas flow, and ultimately reducing stack performance and durability. Therefore, improving fuel cell water management is key to enhancing battery performance and extending battery life.

[0003] Water management in proton exchange membrane fuel cells (PEMFCs) primarily ensures water balance. Effective water management involves draining excess water from the cell without causing dehydration of the proton exchange membrane. During operation, liquid water generated by external humidification and the cathode oxygen reduction reaction binds to the proton exchange membrane to maintain its hydration. Excess liquid water reaches the flow field through the pores of the catalyst layer and gas diffusion layer via capillary action, and is ultimately discharged from the cell by the shear force and capillary effect of the gas flow. Excessive water content in the cell will clog the pores of the porous medium, leading to cathode flooding. In this case, reactant gases are difficult to transport to the catalyst layer (CL), increasing activation losses and concentration losses, ultimately resulting in a significant decrease in discharge performance. Conversely, insufficient water content leads to poor membrane wettability and decreased ionic conductivity, resulting in increased ohmic losses and similarly reduced discharge performance. Therefore, properly controlling the water content in the cell is crucial for its high-performance and stable operation.

[0004] Currently, the most important catalysts in PEMFC operation are Pt-based catalysts, which have high activity, but their poor durability, scarcity, and high cost pose significant challenges to large-scale operation. Generally, the catalytic activity of a catalyst is not only related to its intrinsic catalytic capacity but also largely depends on its surface structure. Therefore, developing new catalysts and support materials is only one part of advancing fuel cell technology. Without simultaneously improving the understanding of the relationship between CL structure and performance, fuel cells will not reach the technological maturity required for widespread commercialization. The morphology of CL is typically determined by the structure and manufacturing method of the support material, both of which play a role in shaping the morphology and performance of CL. The ideal CL structure represents an optimized balance between electrical conductivity, proton conductivity, gaseous reactant transport, and catalyst accessibility.

[0005] The CL slurry is prepared by mixing a catalyst, Nafion solution, and dispersant in a specific ratio, followed by ultrasonic mixing and ultrasonic spraying to prepare the MEA. The transport channels for reactant gases, electrons, protons, and generated water are in a disordered state, leading to strong concentration polarization, which is detrimental to water management in PEMFCs. Constructing a highly permeable MEA provides channels for mass transport, effectively transporting gases, protons, electrons, water, and heat. Therefore, developing a membrane electrode with high porosity and a balanced pore size distribution is crucial for promoting gas transport and aiding water management. Current research on the impact of nanostructured CLs on performance and durability is limited, but they show great potential. Summary of the Invention

[0006] To address the problems and shortcomings of existing technologies, this invention provides a highly drainable porous membrane electrode for fuel cells and its preparation method, aiming to solve the technical problems of low porosity and poor water transport performance in the catalyst layer of existing fuel cell membrane electrodes. Using hydrogen peroxide as a bubble source, oxygen bubbles are generated under carbon-supported platinum catalysis. Micro- and nano-bubbles are used as templates to construct a highly drainable porous membrane electrode. This membrane electrode provides a hierarchical porous catalyst layer with high porosity. Larger pores are set between smaller pores to guide liquid water out in a timely manner, avoiding clogging in smaller pores, optimizing the surface hydrophobicity of the electrode, and mitigating water flooding within the fuel cell.

[0007] This invention discloses a method for preparing a hierarchical porous catalytic layer for a highly drainable porous membrane electrode based on micro / nano bubbles. Hydrogen peroxide is used as the bubble source to generate oxygen bubbles under carbon-supported platinum catalysis. Micro / nano bubbles are then used as templates to construct the highly drainable porous membrane electrode. The method specifically includes the following steps:

[0008] The carbon-supported platinum catalyst PtC was dissolved in ethanol and water to obtain a solution. The solution was ultrasonically treated and then drop-coated onto carbon paper at 80°C. Hydrogen peroxide solution was added dropwise during the coating process. After air drying, the paper was placed in a vacuum freeze-drying oven for further drying.

[0009] The mass fraction of PtC is 40%, and the ratio of PtC to Nafion solution is: the mass fraction of Nafion is 60% of the C in PtC.

[0010] The volume ratio of ethanol to water is 4:1.

[0011] The amount of hydrogen peroxide added is 100 μL; the mass fraction of hydrogen peroxide is 1-2%.

[0012] The vacuum freeze-drying time is 8 hours.

[0013] Furthermore, the present invention discloses a high-porosity membrane electrode, which is prepared by the above method. The membrane electrode can prevent liquid water from clogging the pores and alleviate the flooding phenomenon inside the battery.

[0014] The advantages of this invention are: a high-porosity catalytic layer structure: using hydrogen peroxide as a bubble source, oxygen bubbles are generated under carbon-supported platinum catalysis. Micro- and nano-bubbles are used as templates to construct a high-porosity membrane electrode, effectively preventing liquid water blockage in the pores and alleviating water flooding inside the battery. This invention avoids catalyst particle shrinkage and agglomeration, obtaining a highly drainable porous membrane electrode with a hierarchical porous catalytic layer. This invention also provides the application of the above-mentioned porous membrane electrode in the field of fuel cells. Attached Figure Description

[0015] Figure 1 For Example 1 and Comparative Example 1, 2A cm at 100 kPa -2 A comparison chart of long-term stability.

[0016] Figure 2 The following is a comparison of the stability of Example 1 and Comparative Example 1 under different current densities within 12 hours at 100 kPa; (a) 0.5 A cm -2 (b) 2A cm -2 (c) 2A cm -2 .

[0017] Figure 3 (a) is a comparison graph showing the stability of Example 1 and Comparative Example 1 under different current densities within 12 hours at 150 kPa; (c) 0.5 A cm -2 (b) 2A cm -2 (c) 2A cm -2 (df) is a comparison graph of the stability of Example 1 and Comparative Example 1 under different current densities within 12 hours at 200 kPa; (d) 0.5 A cm -2 ;(e)2A cm -2 ;(f)2A cm-2 .

[0018] Figure 4 In the middle (ac), the scanning electron microscope (SEM) of Comparative Example 1 is shown, and in the middle (df), the scanning electron microscope (SEM) of Example 1 is shown.

[0019] Figure 5 These are contact angle images of Example 1 and Comparative Example 1.

[0020] Figure 6 In Figure 1, a represents the pore number distribution curve of Example 1 and Comparative Example 1, and b represents the pore volume distribution curve of Example 1 and Comparative Example 1. Detailed Implementation

[0021] Example 1:

[0022] 3 mg of 40% PtC and 26.6 μL of Nafion solution were dissolved in 800 μL of ethanol and 200 μL of water. The solution was sonicated. After sonication, the solution was drop-coated onto carbon paper at 80°C, with 100 μL of 1%, 1.5%, and 2% hydrogen peroxide solutions added dropwise during the coating process. After the solution was completely dry, it was dried in a vacuum freeze-drying oven for 8 hours to obtain hp-CL-1, hp-CL-2, and hp-CL-3.

[0023] Comparative Example 1:

[0024] 3 mg of 40% PtC and 26.6 μL of Nafion solution were dissolved in 800 μL of ethanol and 200 μL of water. The solution was sonicated. After sonication, the solution was drop-coated onto carbon paper at 80°C. After the solution was completely dried, it was dried in a vacuum freeze-drying oven for 8 hours to obtain the hierarchical porous membrane electrode c-CL.

[0025] from Figure 1 The results show that hp-CL-1-2 can be stable for more than 156 h, which is higher than that of Pt / C (8 h), indicating that it has excellent stability.

[0026] like Figure 2 As shown in Figure (ac), no reverse polarity phenomenon of the battery was observed in Example 1 within 12 hours, while the reverse polarity phenomenon of the battery in Comparative Example 1 was observed to varying degrees as the current density increased, indicating that Example 1 exhibited excellent stability under different current densities.

[0027] like Figure 3 As shown, no reverse polarity phenomenon of the battery was observed in Example 1 within 12 hours at 150 kPa and 200 kPa, while the reverse polarity phenomenon of the battery in Comparative Example 1 was observed to varying degrees with the increase of current density and pressure, indicating that the stability of the examples was excellent under different pressures.

[0028] pass Figure 4 Comparing the (ac) and (df) images, it can be seen that the surface pore size of Example 1 is larger than that of the comparative example, indicating that Example 1 has a larger pore size and a richer pore structure than the comparative example 1.

[0029] Figure 5 It can be seen that the contact angle of liquid water on different CL surfaces increases with the increase of HP dosage, and the increase in contact angle indicates that the hydrophobicity of CL is enhanced, which is more conducive to water transport.

[0030] Figure 6 It can be seen that Example 1 has a higher porosity than Comparative Example 1, and the pore density of hp-CL-2 near 1000 nm, 50 nm and 10 nm is significantly higher than that of c-CL, indicating the presence of a hierarchical pore structure.

[0031] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a hierarchical porous catalytic layer for a highly permeable porous membrane electrode based on micro / nano bubbles, characterized in that, Using hydrogen peroxide as a bubble source, oxygen bubbles are generated under carbon-supported platinum catalysis. Micro- and nano-bubbles are then used as templates to construct a porous membrane electrode with high water displacement. The specific steps include: The carbon-supported platinum catalyst PtC was dissolved in ethanol and water to obtain a solution. The solution was ultrasonically treated and then drop-coated onto carbon paper at 80°C. Hydrogen peroxide solution was added dropwise during the coating process. After air drying, the paper was placed in a vacuum freeze-drying oven for further drying.

2. The method according to claim 1, characterized in that, The mass fraction of PtC is 40%, and the ratio of PtC to Nafion solution is: the mass fraction of Nafion is 60% of the C in PtC.

3. The method according to claim 1, characterized in that, The volume ratio of ethanol to water is 4:

1.

4. The method according to claim 1, characterized in that, The amount of hydrogen peroxide added is 100 μL; the mass fraction of hydrogen peroxide is 1-2%.

5. The method according to claim 1, characterized in that, The vacuum freeze-drying time is 8 hours.

6. A high-porosity membrane electrode, characterized in that, Prepared using the method described in any one of claims 1-5, the membrane electrode can prevent liquid water from clogging the pores and alleviate the flooding phenomenon inside the battery.

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