Sulfonated polybenzimidazole grafted polyimide proton exchange membrane and preparation method thereof

Abstract

The invention belongs to the technical field of fuel cell proton exchange membrane materials, and relates to a sulfonated polybenzimidazole grafted polyimide proton exchange membrane and a preparation method thereof. The preparation method comprises the following steps: firstly, synthesizing an amino-terminated sulfonated polybenzimidazole prepolymer and carboxyl-containing polyimide, and then forming a branched chain structure through an imidazolation reaction. The grafting modification can introduce a specific molecule or polymer chain into the proton exchange membrane, so that proton exchange sites on the surface of the membrane are increased, the transmission path of protons in the membrane is improved, and the proton conduction performance of the membrane is improved. The introduction of a grafting chain can provide a larger free volume, and adsorption sites of PA are simply and effectively increased, so that the adsorption capacity and retention capacity of PA are increased. A molecular main chain simultaneously contains a polybenzimidazole structure and a polyimide structure, so that the characteristics of the two polymers can be well combined, the N-H bond of the polybenzimidazole is not lost during grafting in the imidazolation reaction, and the condition that the proton conductivity is reduced due to the loss of N-H is avoided.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen fuel cell material technology, and specifically relates to a method for preparing a sulfonated polybenzimidazole-grafted polyimide proton exchange membrane. The obtained sulfonated polybenzimidazole-grafted polyimide proton exchange membrane can be used as a separator in hydrogen fuel cells. Background Technology

[0002] Proton exchange membranes are the core materials of proton exchange membrane fuel cells. Among them, polybenzimidazole (PBI) has excellent thermal stability, good film-forming properties and excellent chemical stability, making it an outstanding proton exchange membrane material.

[0003] PBI is typically synthesized by copolymerizing diacid monomers and tetraammonium monomers. The main chain of PBI contains repeating benzimidazole units. Pure PBI itself lacks proton conductivity and must be doped with phosphoric acid (PA) to construct proton transport channels. Phosphoric acid doping weakens the interaction between the -NH and -N=C groups on the imidazole ring, making the PBI membrane brittle. This limits the level of phosphoric acid doping and restricts the application of PBI membranes in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Furthermore, phosphoric acid is readily soluble in water and prone to leakage, leading to a decrease in proton conductivity. Currently, the doped phosphoric acid is only physically bonded to the PBI polymer chain, not chemically. Therefore, during battery operation, especially in environments with water generation or humidity changes, phosphoric acid molecules easily dissolve and leak from the membrane. This directly reduces the number of proton conduction sites, causing a continuous decline in proton conductivity and ultimately resulting in a sharp decrease in battery performance. To address the aforementioned technical challenges and improve the proton conductivity and mechanical properties of PBI membranes, researchers have undertaken extensive work to enhance PBI, primarily through chemical structure modification, blending, and crosslinking. Grafting modification, in particular, introduces specific molecular or polymer chains into the proton exchange membrane, increasing the number of proton exchange sites on the membrane surface, improving the proton transport path within the membrane, and thus enhancing the membrane's proton conductivity. The introduction of grafted chains provides a larger free volume, effectively and simply increasing the adsorption sites for PA, thereby increasing the adsorption capacity and retention capacity of PA. However, many existing modification methods, while introducing new functional groups, may occupy or disrupt the -NH- groups on the imidazole ring of PBI, which are crucial for proton conduction, thus limiting the upper limit of performance improvement.

[0004] Therefore, developing a novel PBI proton exchange membrane that can significantly improve the phosphoric acid doping level and retention force while perfectly preserving the active sites of the imidazole ring during the modification process is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To overcome the problems in the prior art, the present invention provides a method for preparing a sulfonated polybenzimidazole-grafted polyimide proton exchange membrane from the perspective of improving the performance of the proton exchange membrane. The sulfonated polybenzimidazole-grafted polyimide proton exchange membrane prepared by this method has good mechanical strength and proton conduction performance.

[0006] To achieve the objective of this invention, the technical solution adopted is as follows: a sulfonated polybenzimidazole-grafted polyimide proton exchange membrane, wherein the polymer structure of the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane has the following general formula: ; Wherein: R is either an oxygen group or a sulfone group; m:n = 1:9~9:1.

[0007] The preparation method of the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane as described above includes the following steps: (1) Under nitrogen protection, excess 3,3-diaminobenzidine was fully dissolved in polyphosphoric acid and added to a three-necked flask as a solvent (specifically, polyphosphoric acid was added to the three-necked flask as a solvent, the temperature was raised to 120°C and the air in the polyphosphoric acid was removed, 3,3-diaminobenzidine was added first and the temperature was raised to 140°C and the mixture was stirred to ensure that the 3,3-diaminobenzidine was fully dissolved), and then aromatic dicarboxylic acid was added. and Wherein: R is any one of oxygen or sulfone groups. The temperature is raised to 190℃~200℃ and reacted for 10~12 h. After the reaction is completed, the product is poured into ice water. The filtered product is poured into a carbonate solution of a certain concentration to neutralize the polyphosphoric acid. Then, it is filtered and washed with water and ethanol at least three times to obtain the amino-terminated prepolymer SPBI-Am. The general structural formula of the amino-terminated prepolymer SPBI-Am is as follows: ; (2) Under nitrogen protection, 3,5-diaminoterephthalic acid and 4,4-diaminodiphenyl ether were fully dissolved in N,N-dimethylacetamide solvent, and then an equimolar amount of 4,4-biphenyl ether dianhydride was gradually added. The mixture was then cooled to below 5 °C in an ice-water bath and stirred for 5 h to obtain a polyamic acid solution. This solution was uniformly cast onto a clean glass plate, and the solvent was removed at 80 °C to form a PAA-COOH film. Finally, the PAA-COOH film was transferred to an oven for thermal imidization treatment to obtain PI-COOH, the structural formula of which is as follows: ; (3) Dissolve the amino-terminated SPBI-Am obtained in step (1) and the PI-COOH obtained in step (2) in DMSO, pour the mixed solution onto a clean glass plate, and immediately dry it at 80 °C for 8 h to evaporate the solvent. Then heat-treat it at about 150 °C, and finally place it in an oven at 200 °C for 12 h. Finally, put the membrane into a 1 mol / L hydrochloric acid solution for 48 h for protonation to obtain the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane.

[0008] Furthermore, the 3,3-diaminobenzidine and aromatic dicarboxylic acid mentioned in step (1) are present in polyphosphoric acid at a content of 3wt% to 8wt%.

[0009] Furthermore, the 3,3-diaminobenzidine described in step (1) is in excess by 3% to 6% relative to the aromatic dicarboxylic acid.

[0010] Furthermore, step (1) involves washing the system to pH 7.0-8.0.

[0011] Furthermore, the carbonate mentioned in step (1) is sodium carbonate or sodium bicarbonate, with a concentration of 5wt% to 8wt%.

[0012] Furthermore, the ratio of SPBI-Am to PI-COOH in step (3) is 8:2 to 5:5.

[0013] Furthermore, the heat treatment time at 150 °C in step (3) is 2~3 h.

[0014] The beneficial effects of this invention are as follows: The sulfonated polybenzimidazole-grafted polyimide proton exchange membrane of this invention combines sulfonated polybenzimidazole and polyimide molecules into a single molecule through graft modification. This is achieved by an imidazole reaction between an amino-terminated sulfonated polybenzimidazole (SPBI-Am) prepolymer and a carboxyl-containing polyimide (PI-COOH). The grafting point is precisely positioned at the chain end of the SPBI prepolymer, rather than on the imidazole ring, thereby successfully introducing polyimide segments into the polymer structure without losing any of the crucial -NH- active sites on the imidazole ring for proton conduction. This application provides a novel graft modification scheme, enabling the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane to exhibit excellent proton conductivity.

[0015] Most importantly, the grafted polyimide increases the free volume of the polymer, thereby increasing the phosphoric acid doping level of the proton exchange membrane and thus improving proton conductivity. Furthermore, the increased polar groups form a stronger interaction with phosphoric acid, significantly enhancing the anchoring ability of phosphoric acid molecules and effectively suppressing their loss during use. Simultaneously, the introduction of polyimide segments enhances the rigidity and flexibility of the molecular chain, allowing the membrane material to maintain good mechanical strength and flexibility while possessing a high acid doping rate, successfully overcoming the limitations of traditional PBI membranes in this regard. Attached Figure Description

[0016] Figure 1 The amino-terminated prepolymer prepared in step (1) of Example 1 1 H NMR (DMSO-d6).

[0017] Figure 2 FT-IR of the proton exchange membranes prepared in Examples 1-4.

[0018] Figure 3 The graph shows the change in proton conductivity of the proton exchange membranes prepared in Examples 1-4 as a function of temperature. Detailed Implementation Example 1:

[0019] (1) Synthesis of amino-terminated prepolymer SPBI-NH2 First, 61.00 g of polyphosphoric acid was placed in a 250 mL three-necked flask, nitrogen gas was introduced, and the mixture was stirred and heated to purge excess air. Then, 1.29 g (5.0 mmol) of 4,4-dicarboxylic acid diphenyl ether and 1.34 g (5.0 mmol) of sodium isophthalic acid-5-sulfonate were added, and the mixture was heated to 140 °C and stirred until completely dissolved. Next, 2.27 g (6% excess for aromatic dicarboxylic acids) of 3,3-diaminobenzidine was added, and the mixture was heated to 200 °C and reacted for 8 h. After the reaction was complete, the polymer solution was poured into deionized water and washed thoroughly with plenty of deionized water to remove excess acid. Then, a 5 wt% sodium bicarbonate solution was added for neutralization. The mixture was then filtered and washed with water and ethanol until pH 7.0 was reached. Finally, the product was dried overnight in a 120 °C oven to obtain SPBI-NH2. The product was then subjected to... 1 H NMR characterization, see Figure 1 The assignments of each peak are marked in the spectrum, proving the synthesis of SPBI-NH2.

[0020] (2) Synthesis of carboxyl-containing polyimide PI-COOH In a three-necked flask containing 23 mL of N,N-dimethylacetamide, 1.37 g (9.0 mmol) of 3,5-diaminoterephthalic acid and 0.20 g (1.0 mmol) of 4,4-diaminodiphenyl ether were added, and a clear solution was obtained by mechanical stirring under a nitrogen atmosphere. The mixture was then cooled to below 5 °C in an ice-water bath, and 3.10 g (10.0 mmol) of 4,4-biphenyl ether dianhydride was gradually added. The mixture was stirred for 5 h at below 5 °C to obtain a viscous, homogeneous polyamic acid solution containing carboxylic acid (PAA-COOH). This solution was uniformly cast onto a clean glass plate, and the solvent was removed at 80 °C to form a PAA-COOH film. Finally, the PAA-COOH film was transferred to an oven for thermal imidization treatment: treatment at 100 °C for 1 h, at 200 °C for 2 h, and at 250 °C for 0.5 h, ultimately yielding PI-COOH.

[0021] (3) Preparation of sulfonated polybenzimidazole-grafted polyimide (SPBI-g-PI) proton exchange membrane 0.8 g of amino-terminated sulfonated polybenzimidazole SPBI-NH2 from step (1) and 0.2 g of carboxylated polyimide PI-COOH prepared in step (2) were dissolved in 20 g of dimethyl sulfoxide to prepare a 5 wt% solution. The mixed solution was poured onto a clean glass plate and immediately dried at 80 °C for 8 h to evaporate the solvent, then heat-treated at approximately 150 °C for 2 h, and finally placed in an oven at 200 °C for 12 h. The membrane was then protonated in a 1 mol / L hydrochloric acid solution for 48 h. The prepared membrane was named SPBI-g-20PI proton exchange membrane. The proton exchange membrane was characterized by infrared spectroscopy (see [reference needed]). Figure 2 The SPBI-g-20PI proton exchange membrane has a tensile strength of 82.14 MPa.

[0022] A proton exchange membrane (approximately 45 µm thick) was immersed in an 85% phosphoric acid solution at 80 °C for 24 h. After immersion, the membrane was removed, and residual phosphoric acid was wiped off its surface before testing. The proton conductivity of the proton exchange membrane was measured at 80 °C–160 °C and 20% relative humidity. (See attached data.) Figure 3 The proton conductivity at 160 °C is 135.5 mS / cm. The SPBI-g-20PI proton exchange membrane has a phosphate doping rate of 191.4%.

[0023] Phosphoric acid doping content (%) = [(mass of membrane after phosphoric acid impregnation - mass of membrane before phosphoric acid impregnation) / mass of membrane before phosphoric acid impregnation] * 100%.

[0024] Example 2: 0.7 g of SPBI-NH2 prepared in Example 1 and 0.3 g of PI-COOH prepared in Example 1 were dissolved in 20 g of dimethyl sulfoxide to prepare a 5 wt% solution. The mixed solution was poured onto a clean glass plate and immediately dried at 80 °C for 8 h to evaporate the solvent, then heat-treated at approximately 150 °C for 2 h, and finally placed in an oven at 200 °C for 12 h. The membrane was then protonated by immersing it in a 1 mol / L hydrochloric acid solution for 48 h. The prepared membrane was named SPBI-g-30PI proton exchange membrane. The proton exchange membrane was characterized by infrared spectroscopy (see [reference needed]). Figure 2 ; The proton exchange membrane was immersed in an 85% phosphoric acid solution at 80 °C for 24 h. After immersion, the membrane was removed and the residual phosphoric acid on its surface was wiped off before testing.

[0025] The proton conductivity of the proton exchange membrane was tested at 80 ℃~160 ℃ and 20% relative humidity. (See attached data.) Figure 3 The proton conductivity at 160℃ is 101.4 mS / cm. The SPBI-g-30PI proton exchange membrane has a phosphate doping rate of 181.2%.

[0026] Example 3: 0.6 g of SPBI-NH2 prepared in Example 1 and 0.4 g of PI-COOH prepared in Example 1 were dissolved in 20 g of dimethyl sulfoxide to prepare a 5 wt% solution. The mixed solution was poured onto a clean glass plate and immediately dried at 80 °C for 8 h to evaporate the solvent, then heat-treated at approximately 150 °C for 2 h, and finally placed in an oven at 200 °C for 12 h. The membrane was then protonated by immersing it in a 1 mol / L hydrochloric acid solution for 48 h. The prepared membrane was named SPBI-g-40PI proton exchange membrane. The proton exchange membrane was characterized by infrared spectroscopy, see [reference needed]. Figure 2 ; The proton exchange membrane was immersed in an 85% phosphoric acid solution at 80 °C for 24 h. After immersion, the membrane was removed and the residual phosphoric acid on its surface was wiped off before testing.

[0027] The proton conductivity of the proton exchange membrane was tested at 80 ℃~160 ℃ and 20% relative humidity. (See attached data.) Figure 3 The proton conductivity at 160℃ is 88.6 mS / cm. The SPBI-g-40PI proton exchange membrane has a phosphate doping rate of 146.6%.

[0028] Example 4: 0.5 g of SPBI-NH2 and 0.5 g of PI-COOH prepared in Example 1 were dissolved in 20 g of dimethyl sulfoxide to prepare a 5 wt% solution. The mixed solution was poured onto a clean glass plate and immediately dried at 80 °C for 8 h to evaporate the solvent, then heat-treated at approximately 150 °C for 2 h, and finally placed in an oven at 200 °C for 12 h. The membrane was then protonated by immersing it in a 1 mol / L hydrochloric acid solution for 48 h. The prepared membrane was named SPBI-g-50PI proton exchange membrane. The proton exchange membrane was characterized by infrared spectroscopy (see [reference needed]). Figure 2 ; The proton exchange membrane was immersed in an 85% phosphoric acid solution at 80 °C for 24 h. After immersion, the membrane was removed and the residual phosphoric acid on its surface was wiped off before testing.

[0029] The proton conductivity of the proton exchange membrane was tested at 80 ℃~160 ℃ and 20% relative humidity. (See attached data.) Figure 3 The proton conductivity at 160℃ is 120.9 mS / cm. The SPBI-g-50PI proton exchange membrane has a phosphate doping rate of 141.4%.

[0030] Figure 2 Infrared characterization of the proton exchange membranes prepared in Examples 1-4: The absorption peak observed near 3000 cm⁻¹ can be attributed to the stretching vibration of the CH bond on the benzene ring, indicating the integrity of the benzene ring structure in the SPBI molecule. The characteristic absorption band at 1597 cm⁻¹ corresponds to the stretching vibration of the C=C bond in the aromatic group, further confirming the presence of the benzene ring structure. The characteristic band at 1454 cm⁻¹ originates from the in-plane deformation vibration of the imidazole ring, indicating the stability of the imidazole ring in the SPBI molecule. The absorption peak at 1237 cm⁻¹ is a characteristic signal of the stretching vibration of the CN bond in the imidazole ring, while the absorption peak at 1166 cm⁻¹ corresponds to the stretching vibration of the Ar-O-Ar bond in the polymer backbone, indicating the presence of an aromatic ring structure connected by ether bonds in the polymer chain. The absorption peak at 1041 cm⁻¹ corresponds to the stretching vibration of the sulfonic acid group, confirming that the sulfonic acid group has been successfully introduced into the SPBI molecule. For the PI side chain, typical vibrational modes include symmetric stretching vibrations of the C=N bond, symmetric and asymmetric vibrations of the C=O bond, and deformation vibrations from the imide bicycle. In infrared spectroscopy, the absorption peak at approximately 1779 cm⁻¹ is attributed to the stretching vibrations of the asymmetric C=O bond in the imide ring, while the absorption peak at approximately 1718 cm⁻¹ corresponds to the symmetric stretching vibrations of the C=O bond in the same ring.

[117] Furthermore, the absorption peak at approximately 1354 cm⁻¹ is a characteristic signal of CN bond stretching vibration. The appearance of these characteristic peaks indicates the successful preparation of the SPBI-g-PI composite film.

[0031] Example 5: (1) Synthesis of amino-terminated prepolymer SPBI-NH2 First, 161.00 g of polyphosphoric acid was placed in a 250 mL three-necked flask, and nitrogen gas was introduced, stirred, and heated to purge excess air. Then, 1.53 g (5.0 mmol) of 4,4-dicarboxylic acid biphenyl sulfone and 1.34 g (5.0 mmol) of sodium isophthalic acid-5-sulfonate were added, and the mixture was heated to 140 °C and stirred until completely dissolved. Next, 2.21 g (3% excess) of 3,3-diaminobenzidine was added, and the mixture was heated to 200 °C and reacted for 8 h. After the reaction was complete, the polymer solution was poured into deionized water and washed with plenty of deionized water to remove excess acid. Then, a 5 wt% sodium bicarbonate solution was added for neutralization. The mixture was then filtered and washed with water and ethanol until pH=8.0. Finally, it was dried overnight in a 120 °C oven to obtain SPBI-NH2.

[0032] (2) Synthesis of carboxyl-containing polyimide PI-COOH In a three-necked flask containing 23 mL of N,N-dimethylacetamide, 1.37 g (9.0 mmol) of 3,5-diaminoterephthalic acid and 0.20 g (1.0 mmol) of 4,4-diaminodiphenyl ether were added, and a clear solution was obtained by mechanical stirring under a nitrogen atmosphere. The mixture was then cooled to below 5 °C in an ice-water bath, and 3.10 g (10.0 mmol) of 4,4-biphenyl ether dianhydride was gradually added. The mixture was stirred for 5 h at below 5 °C to obtain a viscous, homogeneous polyamic acid solution containing carboxylic acid (PAA-COOH). This solution was uniformly cast onto a clean glass plate, and the solvent was removed at 80 °C to form a PAA-COOH film. Finally, the PAA-COOH membrane was transferred to an oven for thermal imidization treatment. The specific steps were: treatment at 100 ℃ for 1 h, treatment at 200 ℃ for 2 h, and treatment at 250 ℃ for 0.5 h, to finally obtain PI-COOH.

[0033] (3) Preparation of sulfonated polybenzimidazole-grafted polyimide (SPBI-g-PI) proton exchange membrane 0.8 g of amino-terminated sulfonated polybenzimidazole SPBI-NH2 from step (1) and 0.2 g of carboxylated polyimide PI-COOH prepared in step (2) were dissolved in 20 g of dimethyl sulfoxide to prepare a 5 wt% solution. The mixed solution was poured onto a clean glass plate and immediately dried at 80 °C for 8 h to evaporate the solvent, then heat-treated at approximately 150 °C for 3 h, and finally placed in an oven at 200 °C for 12 h. The membrane was then placed in a 1 mol / L hydrochloric acid solution for 48 h for protonation to obtain a proton exchange membrane.

[0034] The proton exchange membrane was immersed in an 85% phosphoric acid solution at 80 °C for 24 h. After immersion, the membrane was removed and the residual phosphoric acid on its surface was wiped off before testing.

[0035] The conductivity of the proton exchange membrane was tested, and its proton conductivity at 160 °C was 130.7 mS / cm.

[0036] Comparative Example 1: (1) Preparation of SPBI 52.00 g of polyphosphoric acid was added to a three-necked flask purged with nitrogen, and the mixture was heated and stirred to expel air. Next, in the synthesis of SPBI, 1.12 g of 4,4'-dicarboxylic acid diphenyl ether (OBBA) and 1.16 g of sodium isophthalic acid-5-sulfonate (SIPN) were first added to the reaction system and magnetically stirred at 140 °C until completely dissolved. Subsequently, 1.88 g of 3,3'-diaminobenzidine (DAB) was slowly added to the homogeneous solution, and the temperature was gradually increased to 200 °C for a polycondensation reaction lasting 8 h. After the reaction was complete, the polymerized product was poured into deionized water for precipitation, yielding a dark green crude SPBI product. The product was then immersed in a 5 wt% sodium bicarbonate solution and washed at least three times with alternating use of deionized water and ethanol to thoroughly remove residual solvent and small molecule byproducts. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h to obtain pure dark green SPBI.

[0037] (2) Preparation of SPBI proton exchange membrane Dissolve 1.0 g of SPBI from step (1) in 20 g of dimethyl sulfoxide to prepare a 5 wt% solution. Pour the mixed solution onto a clean glass plate and immediately dry it at 80 °C for 8 h to evaporate the solvent. Place the membrane in a 1 mol / L hydrochloric acid solution for 48 h for protonation to obtain a proton exchange membrane.

[0038] The proton exchange membrane was immersed in an 85% phosphoric acid solution at 80 °C for 24 h. After immersion, the membrane was removed and the residual phosphoric acid on its surface was wiped off before testing.

[0039] The conductivity of the proton exchange membrane was tested, and its proton conductivity at 160 °C was 40.0 mS / cm.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sulfonated polybenzimidazole-grafted polyimide proton exchange membrane, characterized in that: The general structural formula of the sulfonated polybenzimidazole-grafted polyimide proton exchange polymer is: ; Wherein: R is either an oxygen group or a sulfone group.

2. A method for preparing a sulfonated polybenzimidazole-grafted polyimide proton exchange membrane as described in claim 1, characterized in that: Includes the following steps: (1) 3,3-diaminobenzidine and aromatic dicarboxylic acid were subjected to polycondensation reaction in polyphosphoric acid to obtain amino-terminated sulfonated polybenzimidazole prepolymer SPBI-Am; The structural formula of aromatic dicarboxylic acids is: and Where R is an oxygen group or a sulfone group; The general structural formula for SPBI-Am is as follows: ; (2) 3,5-diaminoterephthalic acid, 4,4-diaminodiphenyl ether and 4,4-biphenyl ether dianhydride are reacted in N,N-dimethylacetamide solvent to generate a polyamic acid solution, which is then subjected to film formation and thermal imidization treatment to finally obtain carboxyl-containing polyimide PI-COOH; The structural formula of PI-COOH is as follows: ; (3) Dissolve the SPBI-Am obtained in step (1) and the PI-COOH obtained in step (2) in dimethyl sulfoxide, coat the mixed solution with a film, dry it, and then perform a grafting reaction by heat treatment. Finally, perform protonation treatment with acid solution to obtain the sulfonated polybenzimidazole grafted polyimide proton exchange membrane.

3. The method for preparing the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane as described in claim 2, characterized in that: The 3,3-diaminobenzidine described in step (1) is in excess of 3% to 6% of the total molar amount of aromatic dicarboxylic acids.

4. The method for preparing the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane as described in claim 2, characterized in that: The total content of 3,3-diaminobenzidine and aromatic dicarboxylic acid in polyphosphoric acid in step (1) is 3wt%~8wt%.

5. The method for preparing the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane as described in claim 2, characterized in that: In step (1), the temperature of the polycondensation reaction is 190℃~200℃ and the reaction time is 10~12 h.

6. The method for preparing the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane according to claim 2, characterized in that: In step (2), 3,5-diaminoterephthalic acid and 4,4-diaminodiphenyl ether are reacted with an equimolar amount of 4,4-diphenyl ether dianhydride at a temperature below 5°C for 5 h.

7. The method for preparing the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane according to claim 2, characterized in that: The mass ratio of SPBI-Am to PI-COOH in step (3) is 8:2 to 5:

5.

8. The method for preparing the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane according to claim 2, characterized in that: Step (3) heat treatment specifically involves heat treatment at 150 °C for 2-3 h, followed by treatment in an oven at 200 °C for 12 h; the protonation treatment involves immersing the membrane in a 1 mol / L hydrochloric acid solution for 48 h.

9. A proton exchange membrane fuel cell, characterized in that, The fuel cell includes the sulfonated polybenzimidazole-grafted polyimide proton exchange membrane as described in claim 1.

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