Hard-water-resistant multilayer composite proton exchange membrane as well as preparation method and application thereof

Abstract

The invention discloses a hard-water-resistant multilayer composite proton exchange membrane as well as a preparation method and application thereof, and belongs to the technical field of proton exchange membranes. The problems that an existing proton exchange membrane is low in proton conductivity and poor in hard water resistance are solved. The multi-layer composite proton exchange membrane comprises the middle layer and the surface layers on the upper side and the lower side of the middle layer, the middle layer is sulfonated hydrogel in the using process and is provided with a large number of proton channels with large pore diameters, the conduction speed of protons in the membrane is increased, the surface layers are compact in structure, and hydrogen permeation is avoided. According to the invention, the surface polarity and the carbon-containing network of each layer are regulated and controlled through water molecules, so that the compatibility among the layers is improved; besides, a hydrophilic cluster gathering area and a hydrophilic cluster dispersing area are formed in each layer, efficient jumping of protons and swelling water absorption are promoted through a Grottes mechanism, proton diffusion of a carrier mechanism is enhanced, and the proton conductivity and hard water resistance of the proton exchange membrane are improved. The proton exchange membrane can be produced without changing a production line, and has certain economic value.

Description

Technical Field

[0001] This invention belongs to the field of proton exchange membranes, specifically relating to a multilayer composite proton exchange membrane resistant to hard water, its preparation method, and its application. Background Technology

[0002] Against the backdrop of dwindling energy resources and increasingly severe environmental challenges, proton exchange membrane fuel cells (PEMFCs) have attracted widespread attention as a promising green energy conversion technology. As a core component of fuel cells, the performance and cost of the proton exchange membrane (PEM) directly affect the overall system efficiency. Perfluorosulfonic acid (PFSA) ionomers are widely used in the proton exchange membrane field due to their excellent ionic conductivity, low hydrogen permeability, and strong chemical mechanical stability, but they also face key limitations such as high raw material costs and poor resistance to hard water. Traditional proton exchange membranes have extremely high requirements for water quality during operation; circulating water requires high-precision water treatment to avoid the introduction of cationic impurities. When the PFSA membrane comes into contact with a hard water environment containing cationic impurities, the weak binding energy between the sulfonic acid groups and cations leads to the replacement of hydrogen protons by cations, causing the sulfonic acid groups to deactivate, significantly reducing proton conductivity and overall proton transfer efficiency. This deficiency requires PEMFC systems to be equipped with strict gas humidification processes to avoid cation contamination, and their performance will be further deteriorated in marine salt spray environments due to salt contamination, which severely limits their promotion in high-purity environments and marine applications, and increases the operating costs of PEMFC systems.

[0003] Existing fabrication processes for PFSA proton exchange membranes mainly include melt extrusion and solution casting. The differences in the film-forming mechanisms of these two processes lead to significantly different microstructural characteristics within the membrane: under strong shear force, the polymer chains in melt-extruded membranes rearrange along the direction of force to form a dense network, producing small but interconnected hydrophilic clusters; while in solution-cast membranes, the polymer chains are loosely arranged, forming larger but more dispersed hydrophilic clusters. The latter can absorb more free water and exhibit higher proton conductivity under high hydration conditions, but under low hydration conditions, the bound water content of solution-cast membranes is lower than that of melt-extruded membranes, resulting in decreased proton conductivity, and the lack of a dense fluorocarbon chain network puts it at a disadvantage in mechanical strength. However, both methods have the following drawbacks: The core bottleneck of melt extrusion lies in the fact that the sulfonic acid groups in PFSA resin are prone to thermal decomposition and failure during high-temperature processing (typically >250 ℃); the high melt viscosity makes extrusion difficult, hindering the formation of a uniform and defect-free film; simultaneously, the rapid cooling process impedes the full formation of the microphase separation structure necessary for proton conduction, affecting the final performance and proton conductivity. Furthermore, the high-temperature strong acid melt severely corrodes equipment, requiring the use of special corrosion-resistant materials, and additional post-processing steps such as hydrolysis and conversion are needed after film formation; melt extrusion also suffers from anisotropy and uneven filler dispersion issues during proton exchange membrane preparation. Traditional solution casting methods are prone to uneven thickness and edge shrinkage when forming large-area films. Therefore, both preparation methods still have shortcomings, affecting the performance of the proton exchange membrane, resulting in poor hard water resistance and low proton conductivity. Furthermore, existing methods for improving membrane performance often involve introducing inactive components through blending or coating. This not only increases material costs but also inevitably introduces interfacial compatibility issues between different components. Moreover, the poor interfacial compatibility between different single layers of multilayer composite proton exchange membranes makes them prone to cracking and delamination, which also affects proton conductivity and hard water resistance.

[0004] In summary, developing a proton exchange membrane with high proton conductivity and strong resistance to hard water is of great significance for improving the performance and reliability of PEMFCs under complex operating conditions (such as marine environments), reducing system water treatment and operation and maintenance costs, and expanding its application scenarios. Summary of the Invention

[0005] To address the technical problems of low proton conductivity and poor hard water resistance in existing proton exchange membranes, this invention provides a multilayer composite proton exchange membrane resistant to hard water, its preparation method, and its application.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: One of the objectives of this invention is to provide a multilayer composite proton exchange membrane resistant to hard water. The multilayer composite proton exchange membrane includes a surface layer and an intermediate layer. The surface layer is located on the upper and lower sides of the intermediate layer. The surface layer is prepared by coating and drying a surface layer polymer solution made of sulfonated polymer and organic solvent. The intermediate layer is prepared by coating and drying an intermediate layer polymer solution made of sulfonated polymer and organic solvent.

[0007] Further specifying, the sulfonated polymer of the surface layer is one or more of sulfonated polyether ether ketone, sulfonated polyimide, perfluorosulfonic acid, sulfonated polysulfone, and sulfonated polybenzimidazole in any proportion.

[0008] Further specifying, the sulfonated polymer in the intermediate layer is one or more of sulfonated chitosan, sulfonated cellulose, and sulfonated sodium alginate in any proportion.

[0009] Further specifying, the molecular weight of the sulfonated polymer in the surface layer is 50,000 to 1,000,000, and the molecular weight of the sulfonated polymer in the middle layer is 50,000 to 1,000,000.

[0010] Further specified, the thickness of the multilayer composite proton exchange membrane is 15~150 μm.

[0011] A second objective of this invention is to provide a method for preparing the above-mentioned hard water resistant multilayer composite proton exchange membrane, the method comprising the following steps: Step 1: Dissolve the sulfonated polymer used to prepare the surface layer in an organic solvent and stir at 25~80 °C for 0.5~12 h to obtain the surface layer polymer solution; Step 2: Dissolve the sulfonated polymer used to prepare the intermediate layer in an organic solvent and stir at 25~80 °C for 0.5~12 h to obtain the intermediate layer polymer solution; Step 3: Coat the surface layer polymer solution onto the substrate, dry it, then coat the intermediate layer polymer solution, dry it again, then coat the surface layer polymer solution, and finally dry it to obtain a multilayer composite proton exchange membrane.

[0012] Further specifying, the organic solvent in step 1 is one or a mixture of several of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, and dimethyl sulfoxide; the organic solvent in step 2 is one or a mixture of several of N-methylpyrrolidone, N-dimethylformamide, and N-dimethylacetamide.

[0013] Further specifying, in step 1, the mass ratio of sulfonated polymer to organic solvent is (5~50):100, and in step 2, the mass ratio of sulfonated polymer to organic solvent is (5~50):100.

[0014] Further specified, the stirring speed in step 1 is 500~2500 r / min, and the stirring speed in step 2 is 500~2500 r / min.

[0015] Further specifying, the drying temperature in step 3 is 25~200 ℃ and the drying time is 0.5~24 h each time.

[0016] Further specifying, the soaking time in step 4 is 0.5~6 h.

[0017] The third objective of this invention is to provide an application of the aforementioned hard water resistant multilayer composite proton exchange membrane, specifically, the multilayer composite proton exchange membrane is used in a proton exchange membrane fuel cell.

[0018] Furthermore, the intermediate layer of the multilayer composite proton exchange membrane forms a sulfonated hydrogel during use, and the degree of substitution of the sulfonated hydrogel is greater than 1.2.

[0019] The beneficial effects of this invention are as follows: (1) The multilayer composite proton exchange membrane of the present invention is prepared by multiple coating and drying processes of a colloidal proton exchange membrane solution prepared by sulfonated polymer and organic solvent. The middle layer becomes sulfonated hydrogel during use, which has a strong water retention capacity and a large number of proton channels with large pore size, thereby improving the conduction speed of protons in the membrane. The upper and lower sides of the middle layer are covered with a dense surface layer to prevent hydrogen permeation.

[0020] (2) The multilayer composite proton exchange membrane of the present invention improves the compatibility between membrane layers by regulating the surface polarity and carbon-containing branched network of each membrane layer through water molecules, forming a proton exchange membrane with high interfacial compatibility, while enhancing the proton exchange membrane's resistance to hard water. In addition, the present invention achieves the purpose of improving proton conductivity by only changing the single-layer structure, and the performance improvement can be achieved without adding any heterogeneous additives.

[0021] (3) In the surface layer and intermediate layer solution drying stage, this invention utilizes the intrinsic tendency of hydrophilic sulfonic acid groups (-SO3H) to aggregate towards water molecules or with each other, and uses water molecules in the environment to induce the migration of -SO3H in each membrane layer to the membrane surface, thereby regulating the polarity of the membrane surface and increasing the compatibility between different sulfonated polymer layers. At the same time, the mutual attraction between the sulfonic acid groups and water molecules in each membrane layer constructs a continuous gradient distribution of -SO3H groups from the surface to the interior within the membrane, thus forming two forms of hydrophilic clusters in each membrane layer: concentrated distribution and dispersed distribution. The concentrated distribution of hydrophilic clusters on the surface of each membrane layer is the hydrophilic cluster aggregation region, which promotes efficient proton hopping through the Grotthuss mechanism; the dispersed distribution of hydrophilic clusters inside the membrane layer is the hydrophilic cluster dispersion region, which enhances proton diffusion through swelling and water absorption via the vehicle mechanism. Both types of hydrophilic clusters are sulfonic acid groups. This invention integrates the nanoscale interconnected ion cluster structure of melt-extruded films (optimizing the Grotes jump path) with the macroscopic swelling capacity of solution-cast films (enhancing the carrier diffusion path), and simultaneously optimizes the biproton conduction path.

[0022] (4) In the surface layer and intermediate layer solution drying stage, the present invention utilizes water molecules in the environment to induce the migration of -SO3H in each membrane layer to construct different forms of hydrophilic clusters. In addition, the migration of sulfonic acid groups caused by the distribution of sulfonic acid groups induced by water molecules can also drive the swing of the corresponding carbon-containing branches in each membrane layer, forming a network structure between each layer and tightly combining the multilayer structure. This network structure, on the one hand, forms a steric hindrance effect on cations in the environment, hindering the diffusion of cations in the membrane and improving the hard water resistance of the proton exchange membrane. On the other hand, it can also hinder the attack of free radicals on the proton exchange membrane and improve the service durability of the proton exchange membrane.

[0023] (5) This invention employs a combined process of multiple casting and drying, and develops a multi-layer casting technology based on the traditional solution casting process. This technology decomposes a single casting process into a cyclical process of "casting-drying treatment-recasting". The polymer used in the intermediate layer transforms into a sulfonated hydrogel during use, possessing extremely strong water retention capacity and numerous large-pore proton channels, thereby improving the conduction speed of protons within the membrane. The upper and lower sides of the intermediate layer are covered with a dense surface layer, which is a non-hydrogel structure, providing a certain mechanical strength to the proton exchange membrane. Furthermore, the locally dense carbon-containing framework network also enhances the mechanical strength, ensuring the long-term use of the proton exchange membrane. In addition, the proton exchange membrane proposed in this invention can be produced without changing the production line, thus possessing certain economic value.

[0024] (6) The multilayer composite proton exchange membrane of the present invention has a proton conductivity of 0.192 S / cm and a conductivity of 0.028 S / cm after being immersed in 220 ppm hard water at 80 ℃ for 2 hours. This is better than commonly used proton exchange membranes on the market, proving that it has good anti-cation fouling performance and excellent long-term chemical durability. Attached Figure Description Figure 1 The results of proton conductivity tests of the proton exchange membranes of Examples 1, 2 and Comparative Example 1 after immersion in pure water at different temperatures are shown. Figure 2 The results of proton conductivity tests of the proton exchange membranes of Examples 1, 2 and Comparative Example 1 after immersion in hard water at different temperatures are shown. Figure 3 The Raman spectrum of the proton exchange membrane in Example 1; Figure 4 The image shows the Raman spectrum of the proton exchange membrane in Comparative Example 1. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] Example 1 Step 1: Dissolve 0.7 g of sulfonated polyether ether ketone powder with a molecular weight of 180,000 in 7 mL of N-methylpyrrolidone (3.5 g), and stir magnetically at 65 ℃ and 800 r / min for 1 h to obtain a sulfonated polyether ether ketone solution, i.e., a surface layer polymer solution. Step 2: Dissolve 0.7g of sulfonated cellulose powder (purchased from Nanjing Tianlu Nanotechnology Co., Ltd.) with a molecular weight of 400 in 7 mL of N-methylpyrrolidone (3.5g) and stir magnetically at 65 ℃ and 800 r / min for 1 h to obtain a sulfonated cellulose solution, i.e., the intermediate layer polymer solution. Step 3: The sulfonated polyether ether ketone solution obtained in Step 1 is scraped onto the glass substrate and dried at 40 °C for 6 h to form a surface layer located below the intermediate layer. Then, the sulfonated cellulose solution obtained in Step 2 is scraped onto this layer and dried at 40 °C for 6 h to form an intermediate layer. Then, the sulfonated polyether ether ketone solution obtained in Step 1 is scraped onto the intermediate layer and dried at 40 °C for 6 h to form a surface layer located above the intermediate layer, finally obtaining a 30 μm multilayer composite proton exchange membrane. During use, this multilayer composite proton exchange membrane will first fully absorb water and hydrate, during which the middle layer will become a sulfonated hydrogel.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that in step 1, sulfonated polyether ether ketone is replaced with sulfonated polyimide, and in step 2, sulfonated cellulose is replaced with sulfonated chitosan. Comparative Example 1 Step 1: Dissolve 0.7 g of sulfonated polyether ether ketone powder with a molecular weight of 180,000 in 7 mL of N-methylpyrrolidone (3.5 g), and stir magnetically at 65 ℃ and 800 r / min for 1 h to obtain a sulfonated polyether ether ketone solution. Step 2: The sulfonated polyether ether ketone solution obtained in Step 1 is scraped onto a glass substrate and dried at room temperature (40°C) for 18 hours to obtain a 30 μm proton exchange membrane.

[0031] Testing and Experiment Proton conductivity test After immersing the proton exchange membranes from Examples 1-2 and Comparative Examples 1-2 in pure water at different temperatures for 2 hours at room temperature, proton conductivity tests were conducted at a humidity of 100 RH%. The test results are shown in Table 1.

[0032] Table 1. Proton conductivity test results of proton exchange membranes of Examples 1-2 and Comparative Examples 1-2 at different temperatures under pure water conditions.

[0033] As can be seen from Table 1, the proton conductivity of both the examples and the comparative examples increases with increasing temperature. However, at each temperature, the proton conductivity of Examples 1 and 2 is higher than that of Comparative Example 1.

[0034] The proton exchange membranes from Examples 1-2 and Comparative Examples 1-2 were immersed in hard water at 220 ppm and heated at different temperatures for 2 h before proton conductivity tests were performed. The results are shown in Table 2.

[0035] Table 2. Proton conductivity test results of proton exchange membranes of Examples 1-2 and Comparative Examples 1-2 at different temperatures under hard water conditions.

[0036] As can be seen from Table 2, the proton conductivity of the proton exchange membranes in both the examples and the comparative examples decreased after soaking in hard water compared to soaking in pure water. However, Examples 1 and 2 were still significantly better than Comparative Example 1, indicating that the composite proton exchange membrane of the present invention has excellent resistance to hard water.

[0037] Figure 3 , Figure 4 The images show the Raman spectra of Example 1 and Comparative Example 1, respectively, obtained by scanning at regular depths along a cross-section of the proton exchange membrane. Figure 3 As can be seen, the peak intensity first decreases, then increases, and then decreases again with increasing depth. The position where the intensity increases is at the interface between the two membranes in the multilayer composite proton exchange membrane of this invention, where the content of sulfonic acid groups is high and the hydrophilic clusters are dense. Figure 4 and Figure 3 The comparison shows that the Raman spectrum of Comparative Example 1 shows that the peak intensity gradually decreases with increasing depth, which also indicates the induction of surface sulfonic acid groups by water molecules. However, because there is no layered casting, the change is only linear.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multilayer composite proton exchange membrane resistant to hard water, characterized in that, The multilayer composite proton exchange membrane includes a surface layer and an intermediate layer, with the surface layer located on the upper and lower sides of the intermediate layer; The surface layer is prepared by coating and drying a surface polymer solution made of sulfonated polymer and organic solvent. The intermediate layer is prepared by coating and drying an intermediate polymer solution made of sulfonated polymer and organic solvent.

2. The multilayer composite proton exchange membrane according to claim 1, characterized in that, The sulfonated polymer of the surface layer is one or more of sulfonated polyether ether ketone, sulfonated polyimide, perfluorosulfonic acid, sulfonated polysulfone, and sulfonated polybenzimidazole in any proportion; the sulfonated polymer of the middle layer is one or more of sulfonated chitosan, sulfonated cellulose, and sulfonated sodium alginate in any proportion.

3. The multilayer composite proton exchange membrane according to claim 1, characterized in that, The molecular weight of the sulfonated polymer in the surface layer is 50,000 to 1,000,000, and the molecular weight of the sulfonated polymer in the middle layer is 50,000 to 1,000,000.

4. The multilayer composite proton exchange membrane according to claim 1, characterized in that, The thickness of the multilayer composite proton exchange membrane is 15~150 μm.

5. A method for preparing a multilayer composite proton exchange membrane according to any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: Step 1: Dissolve the sulfonated polymer used to prepare the surface layer in an organic solvent and stir at 25~80 °C for 0.5~12 h to obtain the surface layer polymer solution; Step 2: Dissolve the sulfonated polymer used to prepare the intermediate layer in an organic solvent and stir at 25~80 °C for 0.5~12 h to obtain the intermediate layer polymer solution; Step 3: Coat the surface layer polymer solution onto the substrate, dry it, then coat the intermediate layer polymer solution, dry it again, then coat the surface layer polymer solution, and finally dry it to obtain a multilayer composite proton exchange membrane.

6. The preparation method according to claim 5, characterized in that, In step 1, the organic solvent is one or a mixture of several of the following: acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, and dimethyl sulfoxide; the mass ratio of the sulfonated polymer to the organic solvent is (5~50):100; and the stirring speed is 500~2500 r / min.

7. The preparation method according to claim 5, characterized in that, In step 2, the organic solvent is one or a mixture of N-methylpyrrolidone, N-dimethylformamide, and N-dimethylacetamide; the mass ratio of sulfonated polymer to organic solvent is (5~50):100; and the stirring speed is 500~2500 r / min.

8. The preparation method according to claim 5, characterized in that, In step 3, the drying temperature is 25~200 ℃ each time, and the drying time is 0.5~24 h each time; in step 4, the soaking time is 0.5~6 h.

9. An application of the multilayer composite proton exchange membrane according to any one of claims 1 to 4, characterized in that, This multilayer composite proton exchange membrane is used in proton exchange membrane fuel cells.

10. The application according to claim 9, characterized in that, The intermediate layer of the multilayer composite proton exchange membrane forms a sulfonated hydrogel during use, and the degree of substitution of the sulfonated hydrogel is greater than 1.2.

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