Composite proton exchange membrane and preparation method and application thereof

Abstract

The application discloses a composite proton exchange membrane and a preparation method and application thereof. The preparation method of the composite proton exchange membrane comprises the following steps: step 1, electrostatic spinning is performed on a polymer to obtain an electrostatic spinning porous membrane; step 2, a solution containing polybenzimidazole and a composite solvent is poured on the electrostatic spinning porous membrane, and the electrostatic spinning porous membrane is dried and peeled to obtain a nanofiber composite membrane; and step 3, the nanofiber composite membrane is soaked in phosphoric acid for phosphoric acid doping. The composite proton exchange membrane has high proton conductivity, excellent mechanical properties and excellent electrochemical stability.

Description

Technical Field

[0001] This invention relates to the field of high-temperature proton exchange membrane fuel cell technology, specifically to composite proton exchange membranes, their preparation methods, and applications. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are among the most promising clean energy technologies. As the core component of a PEMFC, the proton exchange membrane (PEMFC) plays a crucial role in conducting protons and separating the anode and cathode. Typical low-temperature PEMFCs, such as the commercially available perfluorosulfonic acid (Nafion) membranes, require high humidity to maintain optimal performance. To maintain membrane hydration and prevent flooding, humidity management devices must be incorporated into the fuel cell system. Furthermore, due to the significant heat released by the fuel cell reaction, low-temperature fuel cells also require additional cooling systems. All of these factors significantly increase the complexity and cost of the fuel cell system.

[0003] In contrast, fuel cells can overcome these drawbacks by operating at high temperatures. High-temperature proton exchange membrane fuel cells (HT-PEMFCs) offer the following advantages:

[0004] 1. Avoid catalyst poisoning: CO tolerance increases with increasing temperature, but is almost negligible at high temperatures (140℃).

[0005] 2. Simple water and heat management: The operating temperature is higher than the boiling point of water, so no water management is required; the operating temperature of PEMFC is increased, and the generated heat can be directly recovered and reused, improving battery efficiency.

[0006] 3. Increased conduction rate: At high temperatures, both the conduction rate of protons and the rate at which fuel diffuses to the electrode surface are significantly increased, thus greatly increasing the power output of the fuel cell.

[0007] 4. Low cost: It does not require a complex hydrothermal management system and can reduce the load level of the electrocatalyst used, saving a lot of costs.

[0008] Operating PEMFCs at high temperatures (100-200℃) is considered a potential solution to the technical challenges of low-temperature operation. However, under current technology, water loss from the membrane at high temperatures leads to a sharp decrease in proton conductivity, which in turn reduces the membrane's operating voltage, power, and efficiency at a given current. Furthermore, thermochemical degradation accelerates at high temperatures. Therefore, developing novel high-temperature proton exchange membranes with high thermochemical stability that can operate at high temperatures and low humidity is crucial for the high performance of HT-PEMFCs. Currently, polymer materials that can be used to prepare high-temperature proton exchange membranes include polysulfone (PSU), polyetheretherketone (PEEK), polyimide (PI), polybenzimidazole (PBI), and polyphenylene sulfone (PPS). To date, phosphoric acid-doped PBI systems have become the most promising high-temperature PEMs due to their excellent performance. When phosphoric acid is doped into the PBI membrane (acid doping level greater than 2), the distance between mPBI polymer chains increases due to the plasticizing effect of phosphoric acid, and the intermolecular forces decrease, resulting in a dramatic reduction in the membrane's mechanical strength. Furthermore, highly phosphoric acid-doped mPBI films exhibit significant swelling, leading to reduced film dimensional stability. Summary of the Invention

[0009] To address the aforementioned problems in the existing technology, this invention provides a novel composite proton exchange membrane and its preparation method. The composite proton exchange membrane of this invention exhibits high proton conductivity, excellent mechanical properties, and superior electrochemical stability.

[0010] The first aspect of this invention provides a method for preparing a composite proton exchange membrane, comprising:

[0011] Step 1: Electrospin the polymer to obtain an electrospun porous membrane;

[0012] Step 2: Cast the electrospun porous membrane with a solution containing polybenzimidazole and a composite solvent, and then dry and peel off the membrane to obtain a nanofiber composite membrane.

[0013] Step 3: Immerse the nanofiber composite membrane in phosphoric acid for phosphoric acid doping.

[0014] According to some embodiments of the preparation method of the present invention, step 1 further includes, before electrospinning, mixing the polymer with one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone to obtain a spinning solution.

[0015] According to some embodiments of the preparation method of the present invention, the polymer content in the spinning solution is 10-30% by weight, preferably 15-25% by weight.

[0016] According to some embodiments of the preparation method described in this invention, the electrospinning conditions include: a positive electrospinning voltage of 15 to 18 V, a negative voltage of -0.25 to -0.2 kV, a receiving distance of 10 to 20 cm, a temperature of 35 to 45 °C, and a feed rate of 0.5 to 1.5 mL / h. Preferably, the electrospinning conditions include: a positive electrospinning voltage of 18 kV, a negative voltage of -0.25 kV, a receiving distance of 15 cm, a temperature of 40 °C, and a feed rate of 1.0 mL / h.

[0017] According to some embodiments of the preparation method described in this invention, the polymer is selected from one or more of polyethersulfone, polysulfone, polyphenylene ether, and polyetheretherketone.

[0018] According to some embodiments of the preparation method of the present invention, the composite solvent includes a first component and a second component, wherein the first component is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone; and the second component is selected from one or more of methanol, ethanol and water.

[0019] According to some embodiments of the preparation method of the present invention, the weight ratio of the first component to the second component is 4-10:1-3.

[0020] According to some embodiments of the preparation method of the present invention, in the solution containing polybenzimidazole and a composite solvent, the content of polybenzimidazole is 0.5-5% by weight, and the content of the composite solvent is 95-99.5% by weight.

[0021] According to some embodiments of the preparation method of the present invention, preferably, polybenzimidazole is dissolved in a composite solvent to obtain a solution containing polybenzimidazole and the composite solvent. More preferably, the dissolution temperature is 60-100°C, preferably 70°C, 75°C, 80°C, 85°C, 90°C, or 95°C.

[0022] According to some embodiments of the preparation method described in this invention, the drying temperature is 20-60°C.

[0023] According to some embodiments of the preparation method of the present invention, the conditions for phosphoric acid doping (immersion) include: a temperature of 60-120°C, preferably 80-100°C; and a time of 24-72 h, preferably 36-48 h.

[0024] In some embodiments of the preparation method according to the present invention, the concentration of phosphoric acid is 75-85% by weight, preferably 85% by weight.

[0025] According to some embodiments of the preparation method of the present invention, preferably, after soaking in step 3, the free phosphoric acid on the film surface is wiped dry.

[0026] A second aspect of this invention provides a composite proton exchange membrane prepared by the above method, wherein the thickness of the composite high-temperature proton exchange membrane is 45-70 μm. Within this thickness range, the proton exchange effect is better. The thickness of the composite high-temperature proton exchange membrane can be, for example, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, or 70 μm, and those skilled in the art can set it within this range according to actual needs.

[0027] According to some embodiments of the composite proton exchange membrane of the present invention, the weight ratio of polybenzimidazole, electrospun porous membrane, and phosphoric acid in the composite proton exchange membrane is 5:5:0-20, more preferably, the weight ratio of polybenzimidazole, electrospun porous membrane, and phosphoric acid is 5:5:5-15. Composite proton exchange membranes within the above weight ratio range exhibit superior mechanical properties and proton conductivity.

[0028] The third aspect of the present invention provides a method for preparing the above-described composite proton exchange membrane or the application of the above-described composite proton exchange membrane in a fuel cell, particularly in a proton exchange membrane fuel cell.

[0029] The beneficial effects of this invention are:

[0030] (1) The present invention obtains an electrospun porous membrane by electrospinning and uses it as a mechanical support for a phosphate-doped polybenzimidazole (PBI) system to prepare a composite proton exchange membrane for HT-PEMFC.

[0031] (2) The composite proton exchange membrane of the present invention has excellent mechanical properties, phosphoric acid retention capacity, HT-PEMFC single cell performance, proton conductivity, and can also effectively suppress the swelling of phosphoric acid doped PBI system. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the surface of the composite proton exchange membrane provided in Embodiment 1 of the present invention. Detailed Implementation

[0033] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0034] The testing method and equipment used in this invention are as follows:

[0035] (1) Phosphoric acid doping content: The phosphoric acid doping content was determined by gravimetric method. The mass of the film before (W1) and after (W2) phosphoric acid doping was weighed. The phosphoric acid doping content was calculated by the following formula:

[0036]

[0037] (2) Proton conductivity: The membrane resistance was tested using a frequency response analyzer with a frequency scan range of 0.01-10. 6 The AC signal amplitude was 50mV at Hz. The cut membrane (length × width = 2.4cm × 1cm) was tested using the two-electrode AC impedance method. Before testing, the membrane sample was placed in the test fixture and heated to the specified temperature. The proton conductivity σ (S / cm) of the membrane was calculated using the following formula:

[0038]

[0039] In the formula, L and A are the distance between the two electrodes and the effective cross-sectional area of ​​the membrane under test between the two electrodes, respectively, and R is the resistance of the membrane, which is obtained by the Nyquist plot obtained by AC impedance testing.

[0040] (3) Tensile strength and elongation at break: The membrane was cut into rectangular strips with a length of 40 mm and a width of 10 mm, and tested on an electronic tensile testing machine at a tensile speed of 1 mm / min.

[0041] (4) Acid retention rate: The phosphoric acid-doped membrane was cut into 1×5cm strips and treated at 80℃ and 40%RH for 72h. The proton conductivity σ1 of the membrane was then measured and compared with the initial proton conductivity σ. The acid retention rate was calculated by the following equation:

[0042]

[0043]

Example 1

[0044] (1) Weigh 0.09 g of polyphenylene ether and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0045] (2) Weigh 0.21 g of polybenzimidazole (PBI) and dissolve it in a composite solvent of 16 mL of N,N-dimethylacetamide and 4 mL of n-hexane at 80 °C to form a solution;

[0046] (3) The electrospun film obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 30°C, and the film is peeled off to obtain a nanofiber composite film.

[0047] (4) The nanofiber composite membrane obtained in step (3) is immersed in 85% phosphoric acid at 80°C for 48 hours, and the free phosphoric acid on the membrane surface is wiped dry to obtain a composite proton exchange membrane with a thickness of 60 μm.

[0048] The obtained composite proton exchange membrane was analyzed by electron microscopy, and the surface scanning electron microscope (SEM) image is shown below. Figure 1 As shown.

[0049] Comparative Example 1

[0050] Following the method of Example 1, only the electrospinning in step (1) is omitted, i.e.:

[0051] (1) Weigh 0.21 g of polybenzimidazole (PBI) and dissolve it in a composite solvent of 16 mL of N,N-dimethylacetamide and 4 mL of n-hexane at 80 °C to form a solution;

[0052] (2) Spread polyphenylene ether on a glass plate, then pour the solution obtained in step (1) onto the glass plate, dry at 30°C, peel off the film, and obtain a nanofiber composite film.

[0053] (3) The nanofiber composite membrane obtained in step (2) was immersed in 85% phosphoric acid at 80°C for 48 hours, and the free phosphoric acid on the membrane surface was wiped dry to obtain the comparative composite proton exchange membrane.

[0054] Comparative Example 2

[0055] The method is the same as in Example 1, except that a composite solvent is not used, i.e.:

[0056] (1) Weigh 0.09 g of polyphenylene ether and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0057] (2) Weigh 0.21 g of polybenzimidazole (PBI) and dissolve it in 20 mL of N,N-dimethylacetamide solvent at 80 °C to form a solution;

[0058] (3) The electrospun film obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 30°C, and the film is peeled off to obtain a nanofiber composite film.

[0059] (4) The nanofiber composite membrane obtained in step (3) is immersed in 85% phosphoric acid at 80°C for 48 hours, and the free phosphoric acid on the membrane surface is wiped dry to obtain a composite proton exchange membrane.

[0060] Comparative Example 3

[0061] The method is the same as in Example 1, except that a composite solvent is not used, i.e.:

[0062] (1) Weigh 0.09 g of polyphenylene ether and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0063] (2) Weigh 0.21 g of polybenzimidazole (PBI) and dissolve it in 20 mL of N,N-dimethylformamide at 80 °C to form a solution;

[0064] (3) The electrospun film obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 30°C, and the film is peeled off to obtain a nanofiber composite film.

[0065] (4) The nanofiber composite membrane obtained in step (3) is immersed in 85% phosphoric acid at 80°C for 48 hours, and the free phosphoric acid on the membrane surface is wiped dry to obtain a composite proton exchange membrane.

[0066] Comparative Example 4

[0067] The method is the same as in Example 1, except that step (4) is omitted, i.e.:

[0068] (1) Weigh 0.09 g of polyphenylene ether and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0069] (2) Weigh 0.21 g of polybenzimidazole (PBI) and dissolve it in a composite solvent of 16 mL of N,N-dimethylacetamide and 4 mL of n-pentanol at 80 °C to form a solution;

[0070] (3) The electrospun membrane obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 30°C, and the membrane is peeled off to obtain a nanofiber composite membrane, thus obtaining a composite proton exchange membrane.

[0071]

Test Example 1

[0072] The composite proton exchange membranes prepared in Example 1 and Comparative Examples 1-4 were tested respectively, and the results are shown in Table 1.

[0073] Table 1

[0074] Performance indicators Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Phosphoric acid doping level (ratio of PBI mass) 2.2 2.8 2.7 2.9 0 Proton conductivity (mS / cm, 160℃) 53 58 56 61 0 Tensile strength (MPa) 38 5.9 6.2 6.1 96 Acid retention rate (%, 80℃, 40%RH, 72h) 92 79 77 72 0

[0075] As can be seen from the results in Table 1, the proton conductivity of the phosphoric acid-doped PBI / polyphenylene ether nanofiber composite membrane prepared in Example 1 of this invention is higher than that of the phosphoric acid-doped PBI membrane in Comparative Example 1. Furthermore, the strength and stability of this composite membrane are also significantly improved compared to the phosphoric acid-doped PBI membrane. This meets the requirements for use in high-temperature proton exchange membrane fuel cells.

[0076]

Example 2

[0077] (1) Weigh 0.09 g of polyphenylene ether and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0078] (2) Weigh 0.21g of PBI and dissolve it in a composite solvent of 14mL of N,N-dimethylacetamide and 7mL of n-pentanol at 80℃ to form a solution;

[0079] (3) The electrospun porous membrane obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 40°C, and the membrane is peeled off to obtain a nanofiber composite membrane.

[0080] (4) The nanofiber composite membrane obtained in step (3) is immersed in 85% phosphoric acid at 80°C for 48 hours, and the free phosphoric acid on the membrane surface is wiped dry to obtain a composite proton exchange membrane with a thickness of 60 μm.

[0081]

Example 3

[0082] (1) Weigh 0.09 g of polyethersulfone and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0083] (2) Weigh 0.21g of PBI and dissolve it in a composite solvent of 14mL of N,N-dimethylacetamide and 7mL of n-pentanol at 80℃ to form a solution;

[0084] (3) The electrospun porous membrane obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 30°C, and the membrane is peeled off to obtain a nanofiber composite membrane.

[0085] (4) The nanofiber composite membrane obtained in step (3) is immersed in 85% phosphoric acid at 100°C for 36 hours, and the free phosphoric acid on the membrane surface is wiped dry to obtain a composite proton exchange membrane with a thickness of 45 μm.

[0086]

Example 4

[0087] (1) Weigh 0.09 g of polyether ether ketone and dissolve it in 5 mL of N,N-dimethylformamide under magnetic stirring to form an 18% by weight spinning solution. The electrospinning positive voltage is 18 kV, the negative voltage is -0.25 kV, the receiving distance is 15 cm, the temperature is 40 °C, and the feed rate is 1.0 mL / h. After spinning is completed, an electrospinned porous membrane is obtained.

[0088] (2) Weigh 0.21g of PBI and dissolve it in a composite solvent of 16mL of N,N-dimethylacetamide and 4mL of hexanol at 80℃ to form a solution;

[0089] (3) The electrospun porous membrane obtained in step (1) is laid flat on a glass plate, and then the solution obtained in step (2) is poured onto the glass plate, dried at 20°C, and the membrane is peeled off to obtain a nanofiber composite membrane.

[0090] (4) The nanofiber composite membrane obtained in step (3) is immersed in 85% phosphoric acid at 90°C for 48 hours, and the free phosphoric acid on the membrane surface is wiped dry to obtain a composite proton exchange membrane. The thickness of the composite proton exchange membrane is 45 μm.

[0091]

Test Example 2

[0092] The composite proton exchange membranes prepared in Examples 2-4 were tested respectively, and the results are shown in Table 2.

[0093] Table 2

[0094] Performance indicators Example 2 Example 3 Example 4 Phosphoric acid doping level (ratio of PBI mass) 2.3 2.4 2.6 Proton conductivity (mS / cm, 160℃) 59 59 63 Tensile strength (MPa) 33 31 27 Acid retention rate (%, 80℃, 40%RH, 72h) 88 87 85

[0095] The above description is merely a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, based on the technical teachings provided by the present invention and as common knowledge in the field, other equivalent modifications and improvements can be made, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite proton exchange membrane, comprising: Step 1, electrospinning a polymer to obtain an electrospun porous membrane; the polymer is selected from one or more of polyether sulfone, polysulfone, polyphenyl ether and polyether ether ketone; Step 2, pouring a solution containing polybenzimidazole and a composite solvent onto the electrospun porous membrane, and drying and peeling off the membrane to obtain a nanofiber composite membrane; Step 3, soaking the nanofiber composite membrane in phosphoric acid for phosphoric acid doping; The composite solvent comprises a first component and a second component, the first component is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methyl pyrrolidone; the second component is selected from one or more of heptanol, n-pentanol and n-hexane; The weight ratio of the first component to the second component is 4-10:1-3.

2. The method of claim 1, wherein, The step 1 further comprises mixing the polymer with one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methyl pyrrolidone to obtain a spinning solution before electrospinning.

3. The method of claim 2, wherein, In the spinning solution, the content of the polymer is 10-30% by weight.

4. The method of claim 3, wherein, In the spinning solution, the content of the polymer is 15-25% by weight.

5. The method according to any one of claims 1-4, characterized in that, The electrospinning conditions include: electrospinning positive voltage 15 to 18V, negative voltage -0.25 to -0.2kV, receiving distance 10-20cm, temperature 35 to 45℃, and pushing speed 0.5 to 1.5mL / h.

6. The method of claim 5, wherein, The electrospinning conditions include: electrospinning positive voltage 18kV, negative voltage -0.25kV, receiving distance 15cm, temperature 40℃, and pushing speed 1.0mL / h.

7. The method according to any one of claims 1-4, characterized in that, In the solution containing polybenzimidazole and the composite solvent, the content of polybenzimidazole is 0.5-5% by weight, and the content of the composite solvent is 95-99.5% by weight.

8. The method of claim 7, wherein, Dissolving polybenzimidazole in the composite solvent to obtain a solution containing polybenzimidazole and the composite solvent.

9. The method of claim 8, wherein, The dissolving temperature is 60-100℃.

10. The method of any one of claims 1-4, wherein, The drying temperature is 20-60℃; the phosphoric acid doping conditions include: temperature 60-120℃; time 24-72h; and the concentration of the phosphoric acid is 75-85% by weight.

11. The method of claim 10, wherein, The phosphoric acid doping conditions include: temperature 80-100℃; time 36-48h; and the concentration of the phosphoric acid is 85% by weight.

12. The composite proton exchange membrane prepared by the method of any one of claims 1-11.

13. The composite proton exchange membrane of claim 12, wherein, The thickness of the composite proton exchange membrane is 45-70µm.

14. The use of the composite proton exchange membrane prepared by the method of any one of claims 1-11 or the composite proton exchange membrane of claim 12 or 13 in a fuel cell.

15. The use of the composite proton exchange membrane prepared by the method of any one of claims 1-11 or the composite proton exchange membrane of claim 12 or 13 in a proton exchange membrane fuel cell.

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