A phosphoric acid doped polybenzimidazole high temperature proton exchange membrane and a preparation method thereof

Abstract

The application provides a phosphoric acid doped polybenzimidazole high-temperature proton exchange membrane and a preparation method thereof. In the membrane material, the mass fraction of the phosphoric acid in the polybenzimidazole polymer ranges from more than 0 wt.% to not more than 3000 wt.%. The membrane is prepared through the following steps: S1, dissolving the polybenzimidazole polymer in a solvent, adding phosphoric acid to obtain a composite solution; S2, casting the composite solution on a film forming container, and drying to obtain the phosphoric acid doped polybenzimidazole high-temperature proton exchange membrane. The phosphoric acid doped polybenzimidazole high-temperature proton exchange membrane can not only prepare a stress-free HT-PEM to prevent phosphoric acid loss, but also can arbitrarily and accurately control the phosphoric acid doping amount and the thickness of the prepared membrane through the solution composition and volume, so as to prepare a stress-free phosphoric acid doped polybenzimidazole composite HT-PEM with high stability and ultrahigh specific proton conductivity.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a phosphoric acid-doped polybenzimidazole high-temperature proton exchange membrane and its preparation method. Background Technology

[0002] Due to their strong dependence on high humidity, the operating temperature of proton exchange membrane fuel cells (PEMFCs) using perfluorosulfonic acid (PFSA) matrix proton exchange membranes (PEMs) is limited to below 100°C, leading to complex hydrothermal management systems and high requirements for fuel purity. High-temperature resistant aromatic polymers doped with inorganic acids (represented by phosphoric acid) are considered a major alternative to PEMs operating at temperatures above 120°C under anhydrous conditions. Under these conditions, fuel cells can not only improve CO tolerance but also enhance electrode reaction kinetics and simplify water / thermal management. Recently, many studies on inorganic acid-doped polymer membranes have been reported as high-temperature proton exchange membranes (HT-PEMs). Furthermore, phosphoric acid-doped polybenzimidazole membranes and corresponding membrane electrode assemblies (MEAs) have been successfully commercialized, such as the Fumateck AM membrane and the Celtec-P series MEAs. However, the performance and durability of high-temperature PEMFCs (HT-PEMFCs) still lag significantly behind PFSA-based PEMFCs.

[0003] Besides the well-known reasons for high activation polarization at low current densities due to phosphoric acid catalyst poisoning and high ohmic polarization at medium current densities due to low specific proton conductivity, there is another overlooked factor: the expected high oxygen transport capacity, which should have been achieved by avoiding "flooding," was not. In contrast, reported HT-PEMFCs based on phosphoric acid (PA)-doped polymer membranes exhibit severe concentration polarization, which is more pronounced under back pressure. Therefore, such cells are difficult to operate at high current densities, and their performance cannot meet the practical application requirements of HT-PEMFCs. Furthermore, the stability of phosphoric acid-based HT-PEMFCs remains problematic due to the continuous loss of doped phosphoric acid molecules from the membrane during fuel cell operation. Although various techniques have been applied to embed acid molecules within the membrane, including polymer modification, introduction of foreign species, and cross-linking polymer chains, the loss of phosphoric acid molecules can only be mitigated, not avoided, inevitably leading to a decrease in the anhydrous proton conductivity of the membrane. Current phosphoric acid doping methods are the direct cause of the above problems; the doped phosphoric acid molecules are slowly squeezed out of the polymer membrane by the internal stress generated by separation from the doping environment. When the membrane is assembled into a MEA, this slowly released phosphoric acid enters the catalyst layer and encapsulates the catalyst, causing gas mass transfer resistance and concentration polarization. Furthermore, the loss of phosphoric acid increases the membrane's internal resistance, leading to greater ohmic polarization.

[0004] Therefore, there is an urgent need to develop a new method for preparing phosphoric acid-doped polybenzimidazole high-temperature proton exchange membranes to prepare stress-free phosphoric acid-doped polybenzimidazole composite HT-PEM with high stability and ultra-high specific proton conductivity. Summary of the Invention

[0005] In view of this, the present invention proposes a phosphate-doped polybenzimidazole high-temperature proton exchange membrane with high electrical conductivity, high surface conductivity, low hydrogen permeation, excellent mechanical properties and ultra-long-term stability, and its preparation method.

[0006] In a first aspect, the present invention provides a method for preparing the above-mentioned phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane, comprising the following steps:

[0007] S1. After dissolving the polybenzimidazole polymer in a solvent, phosphoric acid is added to obtain a composite solution;

[0008] S2. Cast the composite solution from step S1 onto a film-forming container and dry it to obtain a phosphate-doped polybenzimidazole high-temperature proton exchange membrane.

[0009] Based on the above technical solutions, preferably, the polybenzimidazole polymer is an aromatic polymer containing a benzimidazole ring structure.

[0010] More preferably, the polybenzimidazole polymer is selected from at least one of poly(2,5-benzimidazole), poly[2,2′-(m-phenylene)-4,4′-bibenzimidazole], poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole], poly[4,4′-(diphenyl ether)-5,5′-biphenyl ether imidazole], or [2,2′-(dihydroxy-1,4-phenylene)-5,5′-bibenzimidazole]. Correspondingly, the polybenzimidazole polymer is selected from at least one of ABPBI, pPBI, mPBI, OPBI, or OHPBI.

[0011] Based on the above technical solutions, preferably, in step S1, the solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone.

[0012] More preferably, the solvent is dimethyl sulfoxide (DMSO).

[0013] By employing the above-mentioned technical solution, dimethyl sulfoxide (DMSO), as a highly efficient solvent, helps to more uniformly disperse and dissolve the polymer during the preparation process, thereby allowing for higher phosphoric acid doping levels. This not only increases the proton conduction pathways within the proton exchange membrane but also further enhances the proton conductivity, resulting in superior conductivity of the final product under high-temperature conditions. Furthermore, the use of DMSO improves material handleability and membrane consistency during the process, ensuring high product quality and stability.

[0014] Based on the above technical solutions, preferably, in the composite solution, the concentration of the polybenzimidazole polymer solution is 0.1-5 wt.%, and the concentration of phosphoric acid is 65-85 wt.%.

[0015] By employing the above technical solution, the composite solution system can efficiently accommodate a high proportion of phosphoric acid while preventing its precipitation. This specific ratio range allows phosphoric acid to be uniformly distributed within the polymer matrix, thereby maximizing proton conductivity without affecting solution stability. The high-temperature proton exchange membrane prepared in this way not only possesses excellent proton conductivity but also exhibits good mechanical strength and thermal stability.

[0016] Based on the above technical solution, preferably, in step S2, the process of casting the composite solution from step S1 onto a flat glass container and drying it to obtain a phosphate-doped polybenzimidazole-based high-temperature proton exchange membrane specifically includes:

[0017] The composite solution from step S1 was cast onto a film-forming container and dried at 100°C for 24 hours. Then, it was dried at 120°C, 140°C, and 160°C for 2 hours each to obtain a phosphate-doped polybenzimidazole high-temperature proton exchange membrane.

[0018] By employing the above-mentioned technical solution, the high-boiling-point solvent can evaporate slowly and uniformly, effectively preventing the loss of phosphoric acid during the drying process. Specifically, this gradient heating drying method not only helps to completely remove residual solvent but also ensures stable doping of phosphoric acid.

[0019] Secondly, the present invention provides a phosphoric acid-doped polybenzimidazole high-temperature proton exchange membrane, wherein the phosphoric acid accounts for a mass fraction of the polybenzimidazole polymer ranging from greater than 0 wt.% to no more than 3000 wt.%.

[0020] Based on the above technical solution, preferably, the phosphoric acid accounts for 1000-2000 wt.% of the mass fraction of the polybenzimidazole polymer.

[0021] By adopting the above technical solution, it is possible to ensure that the high-temperature proton exchange membrane can simultaneously maintain mechanical stability and proton conductivity.

[0022] Based on the above technical solutions, the thickness of the exchange membrane is 5–300 μm.

[0023] Based on the above technical solutions, preferably, the thickness of the exchange membrane is 10 to 100 μm.

[0024] By adopting the above technical solution, within this thickness range, the high-temperature proton exchange membrane can balance surface conductivity and gas barrier properties.

[0025] The present invention provides a phosphate-doped polybenzimidazole-based high-temperature proton exchange membrane and its preparation method, which have the following advantages over the prior art:

[0026] (1) The high-temperature proton exchange membrane and its preparation method provided by the present invention are prepared by directly adding phosphoric acid to a polybenzimidazole polymer solution and casting it into a membrane, and then drying it by gradient heating. The thickness of the prepared membrane and the phosphoric acid doping content can be precisely controlled to obtain a high-temperature proton exchange membrane with ultra-high proton conductivity, surface conductivity and excellent gas barrier capability. The solution in-situ doping technology can also avoid the generation of internal stress in the membrane, thereby preventing the loss of phosphoric acid and greatly improving stability.

[0027] (2) The phosphoric acid-doped polybenzimidazole high-temperature proton exchange membrane of the present invention can not only prepare stress-free HT-PEM to prevent phosphoric acid loss, but also arbitrarily and accurately control the phosphoric acid doping amount and thickness of the membrane by means of solution composition and volume, so as to prepare stress-free phosphoric acid-doped polybenzimidazole composite HT-PEM with high stability and ultra-high specific proton conductivity. This method effectively solves the major challenges of high ohmic polarization and concentration polarization encountered in HT-PEMFC, and at the same time lays the foundation for mitigating catalyst activation polarization caused by phosphoric acid molecule poisoning. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The 1H NMR spectrum of poly[4,4′-(diphenyl ether)-5,5′-biphenyl ether imidazole](OPBI) 1 H NMR spectrum;

[0030] Figure 2 This is a cross-sectional scanning electron microscope (SEM) image of the solution-in-situ composite phosphoric acid-doped OPBI (PA / OPBI) high-temperature proton exchange membrane prepared in Example 1 of the present invention.

[0031] Figure 3 The stress-strain curve of the PA / OPBI high-temperature proton exchange membrane prepared in Example 1 of the present invention is shown.

[0032] Figure 4 The surface conductivity curves of the PA / OPBI high-temperature proton exchange membrane with a thickness of 30 μm and a phosphoric acid doping amount of 1500 wt.% prepared in Example 1 of the present invention are shown at different temperatures.

[0033] Figure 5 The stability of the proton conductivity of the PA / OPBI high-temperature proton exchange membrane with a thickness of 30 μm and a phosphoric acid doping amount of 1500 wt.% prepared in Example 1 of the present invention at 160 °C. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Currently, there are two main methods for preparing high-temperature proton exchange membranes: one is the method widely used in academic literature, which involves first forming the membrane and then immersing it in a phosphoric acid solution; the other is the method commonly used by manufacturers, which involves directly forming the membrane from the reaction solution for synthesizing polybenzimidazole (PBI) (using pyrophosphoric acid as a solvent) and then hydrolyzing it. While both traditional methods have their advantages, they also face some common problems. First, they have significant limitations in controlling membrane thickness and phosphoric acid content, making precise control difficult. Second, and more seriously, the prepared membranes are prone to phosphoric acid loss during practical applications, which not only leads to a rapid decline in material performance but also affects the long-term stability and reliability of the equipment. The root cause of these problems is that the membranes prepared by the above two methods inevitably generate strong internal stress. This internal stress causes phosphoric acid molecules to escape from the membrane structure, thus accelerating phosphoric acid loss.

[0036] Given that existing technologies do not meet the inventor's expectations, the inventor made this invention through further research.

[0037] Based on a deep understanding of the phosphoric acid loss mechanism, the inventors have proposed a novel method for preparing stress-free high-temperature proton exchange membranes. By directly using a phosphoric acid-polymer solution to prepare the membrane, this process not only effectively avoids the generation of internal stress but also ensures that phosphoric acid is uniformly and firmly doped into the polymer matrix. Specifically, this method allows for more precise control over the membrane thickness and phosphoric acid content, resulting in a final product exhibiting excellent mechanical strength, thermal stability, and proton conductivity. Furthermore, by eliminating internal stress, the membrane can significantly reduce phosphoric acid loss in practical applications, maintain stable performance, and extend its service life. Therefore, this invention provides a more efficient, reliable, and easily industrialized preparation method, offering solid technical support for high-performance applications such as high-temperature fuel cells.

[0038] The high-temperature proton exchange membrane and its preparation method according to embodiments of the present invention will be described in detail below.

[0039] This invention provides a method for preparing a solution-in-situ composite phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane, which includes the following steps:

[0040] The polybenzimidazole polymer is dissolved in a solvent, and then phosphoric acid is added to the solution.

[0041] The composite solution is cast onto a film-forming container, such as a flat glass container or a container made of polytetrafluoroethylene, and then dried to obtain the high-temperature proton exchange membrane.

[0042] In this invention, the polybenzimidazole polymers are selected from aromatic polymers containing benzimidazole ring structures, such as poly(2,5-benzimidazole), poly[2,2′-(m-phenylene)-4,4′-bibenzimidazole], poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole], poly[4,4′-(diphenyl ether)-5,5′-biphenyl ether imidazole], or [2,2′-(dihydroxy-1,4-phenylene)-5,5′-bibenzimidazole].

[0043] In this invention, the solvent is any one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone, and the concentration of the polybenzimidazole polymer solution is 0.1-5 wt.%. Preferably, in a preferred embodiment of this invention, the solvent is dimethyl sulfoxide, which allows the resulting composite film to be doped with more phosphoric acid and has higher proton conductivity. Preferably, the solution concentration is 0.1, 0.5, 1, 3, 5 wt.%, etc., as polymer solution systems with such concentrations can further incorporate phosphoric acid.

[0044] In this invention, the phosphoric acid concentration is 65-85 wt.%. Preferably, the phosphoric acid concentration is 65, 70, 75, 80, or 85 wt.%, etc., to ensure that the polymer does not precipitate from the solution. The mass fraction of the phosphoric acid relative to the polybenzimidazole polymer is 0-3000 wt.%, preferably 1000-2000 wt., to ensure that the resulting membrane simultaneously maintains mechanical stability and proton conductivity.

[0045] In this invention, drying is first carried out at 100°C for 24 hours, allowing the high-boiling-point solvent to evaporate slowly and ensuring that the phosphoric acid in the membrane is not lost during the drying process. Subsequently, drying is carried out at 120°C, 140°C, and 160°C for 2 hours respectively, ensuring that the phosphoric acid is not lost during the drying process while the solvent is completely removed.

[0046] The solution-in-situ composite phosphate-doped polybenzimidazole high-temperature proton exchange membrane prepared in this invention has a thickness of 5-300 μm. Preferably, the thickness is 10-100 μm. Within this thickness range, the high-temperature proton exchange membrane can balance surface conductivity and gas barrier properties. The thickness of the composite proton exchange membrane can be, for example, 10 μm, 40 μm, 70 μm, or 100 μm, etc., and those skilled in the art can set it within this range according to actual needs.

[0047] The features and performance of the present invention will be further described in detail below with reference to the embodiments. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0048] The phosphate-doped polybenzimidazole-based high-temperature proton exchange membranes prepared in the following examples and comparative examples were subjected to the following performance tests, including:

[0049] (1) Proton conductivity and surface conductivity testing

[0050] The test was conducted using a frequency response analyzer, with a frequency scan range of 1–10. 6 The AC signal amplitude was 50mV at Hz. The membrane materials prepared in each embodiment and comparative example were cut to a size of 2.5cm × 1cm (length × width). Two-electrode AC impedance spectroscopy was used for testing. Before testing, the membrane samples were equilibrated at 160℃ for 0.5 hours. The proton conductivity σ (mS / cm) and surface conductivity (SPC, S / cm) of the membrane were measured. -2 The calculation is performed using the following formula:

[0051]

[0052] SPC = σ / d;

[0053] 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; R is the resistance of the membrane, which is obtained by the Nyquist plot obtained by AC impedance testing; and d is the thickness of the membrane.

[0054] (2) Tensile strength and elongation at break tests

[0055] The membrane was cut into rectangular strips 80 mm long and 10 mm wide, and tested on an electronic tensile testing machine at a tensile speed of 1 mm / min, with a temperature of 25℃ and a humidity of 50% RH.

[0056] (3) Hydrogen permeation current density

[0057] The hydrogen permeation current density of the membrane electrode (PEM) was measured using linear sweep voltammetry (LSV) to characterize its gas barrier properties. Before testing, nitrogen gas was introduced through both sides of the electrode to purge the cell voltage to below 0.1 V. During the test, 200 mL / min was introduced into both the anode and cathode. -1 H2 and nitrogen, at 30°C and without back pressure, at a rate of 2 mV·s -1 The scan rate was from 0.1V to 0.7V. In this experiment, the hydrogen permeation current density (j) at 0.4V was used. H2@0.4V The size characterizes the hydrogen permeation of the membrane.

[0058] Example 1

[0059] The phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane of this embodiment is obtained through the following steps:

[0060] (1) Dissolve 0.1g of OPBI in 20g of dimethyl sulfoxide at 100℃ to form a 0.5wt.% solution; then add 1.76g of 85% phosphoric acid solution dropwise to the solution system and continue stirring for 1 hour to obtain a composite solution;

[0061] (2) The composite solution in step 1 is cast onto a flat glass container and dried at 100°C for 24 hours. Then, it is dried at 120°C, 140°C and 160°C for 2 hours respectively to obtain a phosphoric acid-doped OPBI (PA / OPBI) high-temperature proton exchange membrane with a phosphoric acid doping content of 1500wt.% and a thickness of 30μm.

[0062] The proton exchange membrane prepared in this embodiment was subjected to the above-mentioned performance tests, and the performance test results are shown in Table 1.

[0063] Table 1 Performance Test Results

[0064] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 366 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 122.1 Tensile strength (MPa) 3.8 Elongation at break (%) 362 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 0.45

[0065] Comparative Example 1

[0066] This comparative example shows a phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane prepared using a conventional membrane preparation strategy. The specific preparation steps are as follows, and the performance test results are shown in Table 2.

[0067] (1) Dissolve 0.3g of OPBI in dimethyl sulfoxide at 100℃ to form a 1wt.% solution. Then cast the solution onto a flat glass container and dry it at 100℃ for 24 hours, followed by drying at 160℃ for 2 hours.

[0068] (2) The OPBI membrane from step (1) was immersed in 85 wt.% phosphoric acid at 160°C for 2 hours. The membrane was then removed and the surface phosphoric acid was wiped dry to obtain a phosphoric acid-doped OPBI (PA / OPBI) high-temperature proton exchange membrane with a phosphoric acid doping content of 620 wt.% and a thickness of 95 μm.

[0069] Table 2 Performance Test Results

[0070] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 133 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 14 Tensile strength (MPa) 9 Elongation at break (%) 182 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 2.1

[0071] Combining the performance test results in Tables 1 and 2, it can be seen that the PA / OPBI high-temperature proton exchange membrane prepared by solution in situ composite in Example 1 has higher proton conductivity, surface conductivity and toughness than the PA / OPBI high-temperature proton exchange membrane prepared by the traditional membrane preparation strategy. At the same time, the gas barrier properties of this membrane are also significantly better than those of the traditional membrane, which can meet the requirements for use in high-temperature proton exchange membrane fuel cells.

[0072] In addition, from Figure 1 The 1H NMR spectrum confirmed that the polymer used had an OPBI structure; from Figure 2 It can be seen from the data that the prepared PA / OPBI film is relatively smooth and free of defects such as cracks; Figure 3 The tensile strength of the prepared membrane was confirmed to be 3.8 MPa, which meets the application requirements of fuel cells. Figure 4 This indicates that the proton surface conductivity of the prepared membrane can reach 122.1 S / cm. 2 ; Figure 5 This indicates that the proton conductivity of the prepared PA / OPBI film did not decrease significantly within 1200 hours at 160℃.

[0073] Example 2

[0074] The phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane of this embodiment is obtained through the following steps:

[0075] (1) Dissolve 0.1g of pPBI in 20g of N-methylpyrrolidone at 100℃ to form a 0.5wt.% solution; then add 1.76g of 85% phosphoric acid solution dropwise to the above system and continue stirring for 1 hour to obtain a composite solution;

[0076] (2) The composite solution in step 1 is cast onto a flat glass container and dried at 100°C for 24 hours. Then, it is dried at 120°C, 140°C and 160°C for 2 hours respectively to obtain a phosphoric acid doped pPBI (PA / pPBI) high-temperature proton exchange membrane with a phosphoric acid doping content of 500wt.% and a thickness of 100μm.

[0077] The performance test results are shown in Table 3.

[0078] Table 3 Performance Test Results

[0079] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 78 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 7.8 Tensile strength (MPa) 8.3 Elongation at break (%) 147 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 0.12

[0080] Comparative Example 2

[0081] The difference from Example 2 is that in step (1), 0.1 g of pPBI was dissolved in N-methylpyrrolidone at 100°C to form a 0.08 wt.% solution, while the remaining steps remained unchanged. The performance test results are shown in Table 4.

[0082] Table 4 Performance Test Results

[0083] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 65 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 6.5 Tensile strength (MPa) 7.9 Elongation at break (%) 135 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 0.14

[0084] Comparative Example 3

[0085] The difference from Example 2 is that in step (1), 0.1 g of pPBI was dissolved in N-methylpyrrolidone at 100 °C to form a 5.5 wt.% solution, while the remaining steps remained unchanged. The performance test results are shown in Table 5.

[0086] Table 5 Performance Test Results

[0087]

[0088]

[0089] Comparing the performance test results of Example 2 and Comparative Examples 2-3, it can be seen that: in Comparative Example 2, due to the lower polymer concentration, the phosphoric acid doping amount is relatively high, but the film structure may not be dense enough, thus the proton conductivity and surface conductivity are slightly reduced. In Comparative Example 3, the higher polymer concentration makes the film structure more dense, but the phosphoric acid doping amount is relatively reduced, thus the proton conductivity and surface conductivity are slightly lower.

[0090] Example 3

[0091] The phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane of this embodiment is obtained through the following steps:

[0092] (1) Dissolve 0.1g of OPBI in 100g of dimethyl sulfoxide at 100℃ to form a 0.1wt.% solution; then add 1.76g of 85% phosphoric acid solution dropwise to the solution system and continue stirring for 1 hour to obtain a composite solution;

[0093] (2) The composite solution in step 1 is cast onto a flat glass container and dried at 100°C for 24 hours. Then, it is dried at 120°C, 140°C and 160°C for 2 hours respectively to obtain a phosphoric acid-doped OPBI (PA / OPBI) high-temperature proton exchange membrane with a phosphoric acid doping content of 1000wt.% and a thickness of 10μm.

[0094] The performance test results are shown in Table 6.

[0095] Table 6 Performance Test Results

[0096] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 162 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 81 Tensile strength (MPa) 2.8 Elongation at break (%) 236 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 0.50

[0097] Comparative Example 4

[0098] The difference from Example 3 is that in step (2), the composite solution in step 1 is cast onto a flat glass container and dried at 100°C for 30 hours to obtain a phosphoric acid-doped OPBI (PA / OPBI) high-temperature proton exchange membrane with a phosphoric acid doping content of 1000wt.% and a thickness of 10μm.

[0099] The performance test results are shown in Table 7.

[0100] Table 7 Performance Test Results

[0101] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 158 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 79 Tensile strength (MPa) 1.2 Elongation at break (%) 107 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 1.25

[0102] By comparing Example 3 and Comparative Example 4, we can see that if a gradient heating drying method is not adopted, the polymer will have weaker cross-linking and entanglement during the film formation process, which will lead to a decrease in its mechanical strength and an increase in hydrogen permeability.

[0103] Example 4

[0104] The phosphoric acid-doped polybenzimidazole-based high-temperature proton exchange membrane of this embodiment is obtained through the following steps:

[0105] (1) Dissolve 0.1g of OPBI in 1.9g of dimethyl sulfoxide at 100℃ to form a 5wt.% solution; then add 1.76g of phosphoric acid dropwise to the solution system and continue stirring for 1 hour to obtain a composite solution;

[0106] (2) The composite solution in step 1 is cast onto a flat glass container and dried at 100°C for 24 hours. Then, it is dried at 120°C, 140°C and 160°C for 2 hours respectively to obtain a phosphoric acid doped OPBI (PA / OPBI) high-temperature proton exchange membrane with a phosphoric acid doping content of 2000wt.% and a thickness of 50μm.

[0107] The performance test results are shown in Table 8.

[0108] Table 8 Performance Test Results

[0109]

[0110]

[0111] Example 5

[0112] The difference from Example 4 is that the OPBI (PA / OPBI) high-temperature proton exchange membrane with phosphoric acid doping content of 3000 wt.% and thickness of 5 μm is phosphoric acid doped.

[0113] The performance test results are shown in Table 9.

[0114] Table 9 Performance Test Results

[0115] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 289 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 578 Tensile strength (MPa) 0.7 Elongation at break (%) 143 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 1.87

[0116] Comparing Examples 1 and 3-5, it can be seen that when the phosphoric acid doping content is 1000-2000 wt.% and the membrane thickness is 10-100 μm, the mechanical properties of the membrane can meet the requirements of fuel cell assembly, and the hydrogen permeability is also low. Although thinner membranes have extremely high proton conductivity, their mechanical strength is low, making them difficult to apply in practice.

[0117] Using Example 1 as an example, the inventors obtained Examples 6 to 10 by changing the solvent, as shown in Table 10, and recorded the performance test results in Table 11 below.

[0118] Table 10 Solvent Types

[0119]

[0120] Table 11 Performance Test Results

[0121]

[0122] By comparing Examples 6-10 and Example 1, it can be seen that: when the solvent is dimethyl sulfoxide, the resulting composite membrane can be doped with more phosphoric acid and has a higher proton conductivity. Since the membrane thickness is similar, the mechanical properties and hydrogen permeation current are not significantly different.

[0123] Comparative Example 5

[0124] The difference from Example 5 is that a commercial polyphenylene ether with a number-average molecular weight of 67 kDa was used instead of polybenzimidazole for comparison. The performance test results are shown in Table 12.

[0125] Table 12 Performance Test Results

[0126] Performance indicators Test Results Proton conductivity (mS / cm, 160℃) 172 <![CDATA[Surface conductivity (S / cm 2 , 160 °C)]]> 344 Tensile strength (MPa) 0.67 Elongation at break (%) 129 <![CDATA[Hydrogen permeation current density (mA·cm -2 )]]> 1.02

[0127] As shown in Table 12, aromatic polymers containing benzimidazole ring structures exhibit better overall performance.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a phosphate-doped polybenzimidazole-based high-temperature proton exchange membrane, characterized in that, Includes the following steps: S1. After dissolving the polybenzimidazole polymer in a solvent, phosphoric acid is added to obtain a composite solution; S2. The composite solution from step S1 is cast onto a flat glass container and dried at 100°C for 24 hours. Then, it is dried at 120°C, 140°C and 160°C for 2 hours each to obtain a phosphoric acid-doped polybenzimidazole high-temperature proton exchange membrane. In step S1, the solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone; In the composite solution, the concentration of the polybenzimidazole polymer solution is 0.1-5 wt.%, and the concentration of phosphoric acid is 65-85 wt.%.

2. The method for preparing a phosphate-doped polybenzimidazole-based high-temperature proton exchange membrane as described in claim 1, characterized in that, The polybenzimidazole polymer is an aromatic polymer containing a benzimidazole ring structure.

3. The method for preparing a phosphate-doped polybenzimidazole-based high-temperature proton exchange membrane as described in claim 2, characterized in that, The polybenzimidazole polymer is selected from at least one of poly(2,5-benzimidazole), poly[2,2′-(m-phenylene)-4,4′-bibenzimidazole], poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole], poly[4,4′-(diphenyl ether)-5,5′-biphenyl ether imidazole] or [2,2′-(dihydroxy-1,4-phenylene)-5,5′-bibenzimidazole].

4. A phosphate-doped polybenzimidazole-based high-temperature proton exchange membrane prepared by the preparation method according to any one of claims 1 to 3, characterized in that, The phosphoric acid constitutes a mass fraction of the polybenzimidazole polymer that is greater than 0 wt.% and does not exceed 3000 wt.%.

5. The phosphate-doped polybenzimidazole high-temperature proton exchange membrane as described in claim 4, characterized in that, The phosphoric acid accounts for 1000-2000 wt.% of the mass fraction of the polybenzimidazole polymer.

6. The phosphate-doped polybenzimidazole high-temperature proton exchange membrane as described in claim 5, characterized in that, The thickness of the exchange membrane is 5~300μm.

7. The phosphoric acid-doped polybenzimidazole high-temperature proton exchange membrane as described in claim 6, characterized in that, The thickness of the exchange membrane is 10~100μm.

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