A starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membrane, and a preparation method and application thereof

Abstract

This invention belongs to the field of fuel cell material technology and discloses a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide, its preparation method, and its application. A graphene oxide aqueous dispersion is mixed and reacted with phosphorus pentoxide, and then starch is added to obtain a phosphoric acid system containing graphene oxide and starch. This system is mixed with phosphorus pentoxide and heated and stirred to obtain a polyphosphoric acid system containing graphene oxide and starch. Under nitrogen protection, 3,3'-diaminobenzidine and 4,4'-dicarboxylic acid diphenyl ether are added to the polyphosphoric acid system for in-situ polymerization to obtain a hot slurry liquid. The slurry liquid is coated onto a preheated glass plate using a direct membrane deposition method. After standing, peeling, and vacuum drying, the starch- and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membrane is obtained. The exchange membrane has good thermal stability, mechanical properties, and oxidation resistance. The process is simple, the raw materials are readily available, and it is suitable for high-temperature proton exchange membrane fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell material technology, specifically relating to a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide, its preparation method, and its application. Background Technology

[0002] The proton exchange membrane (PEM) is a key component of a proton exchange membrane fuel cell (PEMFC), its main function being to conduct protons and isolate fuel and oxidant during operation. Compared to low-temperature PEMFCs, high-temperature PEMFCs can operate under higher temperature and lower humidity conditions, which is beneficial for improving the fuel cell's tolerance to impurities such as carbon monoxide and simplifying the hydrothermal management system. Therefore, developing high-temperature PEMFCs suitable for operation under high temperature, low humidity, or no-humidification conditions is of great significance.

[0003] Polybenzimidazole composite membranes possess good thermal stability, chemical stability, and mechanical properties. After being doped with phosphoric acid, they can conduct protons under high-temperature, humidified conditions, making them an important candidate material for high-temperature proton exchange membranes. However, traditional phosphoric acid-doped polybenzimidazole composite membranes may still suffer from phosphoric acid loss, proton conductivity decay, and mechanical property degradation during long-term high-temperature operation. The retention capacity of phosphoric acid within the membrane, the continuity of the proton transport channels within the membrane, and the stability of the polymer matrix are important factors affecting the overall performance of high-temperature proton exchange membranes.

[0004] Starch is a widely available and low-cost natural polymer material. Its molecular structure contains numerous oxygen-containing groups such as hydroxyl groups, which can form hydrogen bonds with phosphate and polymer segments, facilitating the construction of a high-density hydrogen bond network within the membrane and thus improving proton conductivity. Graphene oxide, with its layered structure and abundant oxygen-containing functional groups, can participate as a functional nanocomponent in the construction of composite membrane structures. If starch and graphene oxide can be introduced simultaneously during the in-situ polymerization of polybenzimidazole, allowing the functional components to be fully dispersed and bonded to the polymer matrix during polymerization and film formation, it is expected to obtain a high-temperature proton exchange membrane with high proton conductivity, good phosphate retention capacity, good mechanical properties, and oxidation resistance. Summary of the Invention

[0005] Based on the above, this invention provides a method for preparing a high-temperature proton exchange membrane using an in-situ polymerization-direct membrane deposition method. This method is environmentally friendly, uses widely available raw materials, is simple to prepare, low in cost, and easy to mass-produce. Using polybenzimidazole as the base material, this invention creatively introduces starch and graphene oxide to effectively construct a high-density hydrogen bond network structure, thereby effectively improving proton conductivity. The materials used are green, non-toxic, harmless, and pollution-free, conforming to the trend of green and environmentally friendly development and reflecting an environmentally friendly strategy.

[0006] The present invention aims to provide a method for preparing a high-temperature proton exchange membrane of polybenzimidazole synergistically modified with starch and graphene oxide, comprising the following steps: 1) Preparation of polyphosphoric acid containing graphene oxide and starch: Aqueous dispersion of graphene oxide is mixed with phosphorus pentoxide, and the phosphorus pentoxide reacts with water in the aqueous dispersion of graphene oxide. After the reaction is carried out under heating conditions, starch is added to obtain a phosphoric acid system containing graphene oxide and starch. The phosphoric acid system containing graphene oxide and starch is then mixed with phosphorus pentoxide and heated and stirred until a homogeneous solution is formed to obtain polyphosphoric acid containing graphene oxide and starch.

[0007] Furthermore, the concentration of the graphene oxide aqueous dispersion is 1 mg / mL-4 mg / mL; phosphorus pentoxide is mixed with water in the graphene oxide aqueous dispersion at a molar ratio of 1:(2-5) and reacted at 60℃-100℃ for 0.5h-1h. The starch content is 1wt%-5wt%; the phosphoric acid system containing graphene oxide and starch is mixed with phosphorus pentoxide at a mass ratio of 1:(1-2) and stirred at 100℃-120℃ for 4h-6h.

[0008] 2) In-situ polymerization reaction: Under nitrogen protection, 3,3'-diaminobenzidine and 4,4'-dicarboxylic acid diphenyl ether are added to the polyphosphoric acid system containing graphene oxide and starch prepared in step 1) and a segmented heating in-situ polymerization reaction is carried out to obtain a hot slurry liquid.

[0009] Furthermore, the molar ratio of 3,3'-diaminobenzidine to 4,4'-dicarboxylic diphenyl ether is 1:1. The total solid content of 3,3'-diaminobenzidine and 4,4'-dicarboxylic diphenyl ether in the reaction system is 1.5 w / v%-15 w / v.

[0010] Furthermore, the segmented heating in-situ polymerization reaction includes: first, mechanical stirring at 70℃-120℃ for 0.5h-2h, then heating to 140℃-170℃ for 5h-10h, followed by heating to 180℃-200℃ for 8h-10h.

[0011] 3) Direct membrane deposition and post-treatment: The hot slurry liquid obtained in step 2) is coated onto a preheated glass plate and allowed to stand in a constant temperature and humidity chamber to form a membrane. After membrane formation, the membrane is peeled off from the glass plate, the liquid on the membrane surface is removed, and vacuum drying is performed to obtain a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide.

[0012] Furthermore, the preheating temperature of the glass plate is 80℃-100℃, the temperature of the constant temperature and humidity chamber is 25℃-35℃, the humidity is 45%-85%, the static film formation time is 3-21 days, the vacuum drying temperature is 80℃-120℃, and the vacuum drying time is 12h-36h.

[0013] A polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide is prepared by the above method.

[0014] An application of a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide in the field of proton exchange membrane fuel cells.

[0015] The significant advantages of this invention compared to the prior art are as follows: 1) This invention uses in-situ polymerization-direct film laying method to prepare composite film, so that starch and graphene oxide are fully compounded with polymer matrix during the formation of polybenzimidazole, avoiding the problem of uneven dispersion of functional components in simple post-blending method.

[0016] 2) This invention introduces starch into the polyphosphate system. Starch molecules contain abundant oxygen-containing groups such as hydroxyl groups, which is beneficial to improving the phosphate retention capacity of the membrane and forming a continuous channel that is conducive to proton transport.

[0017] 3) The present invention introduces graphene oxide as a functional nanocomponent, which is beneficial to improving the structural stability and overall performance of the composite membrane.

[0018] 4) The preparation process of this invention is simple, mainly including the preparation of polyphosphoric acid system, in-situ polymerization, direct film laying, static film formation and vacuum drying, etc. It does not require complex equipment and is suitable for further scale-up preparation.

[0019] 5) The composite membrane prepared by this invention exhibits high high-temperature proton conductivity. Under humidification conditions, the prepared composite membrane achieves a proton conductivity of 0.224 S cm⁻¹ at 160°C. -1 At 180℃, the proton conductivity can reach 0.256 S cm. -1 At 240℃, the proton conductivity can reach 0.354 S cm. -1 .

[0020] 6) The composite membrane prepared by this invention exhibits good durability. After continuous testing at 200°C for 600 minutes, the proton conductivity of the prepared composite membrane remains at 0.150 S cm⁻¹. -1 above.

[0021] 7) The composite membrane prepared by this invention has good thermal stability before 220°C, and can still maintain the integrity of the membrane morphology after being soaked in Fenton's reagent at room temperature for 120 h, and has good oxidation resistance. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of the polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide as described in this invention. Figure 2 The infrared spectrum of the composite film prepared in the embodiment of the present invention; Figure 3 X-ray diffraction pattern of the composite film prepared in an embodiment of the present invention; Figure 4 Thermogravimetric analysis diagram of the composite membrane prepared in the embodiment of the present invention; Figure 5 Differential thermogravimetric analysis (TGA) curve of the composite membrane prepared in an embodiment of the present invention; Figure 6 The graph shows the proton conductivity test results of the composite membrane prepared in an embodiment of the present invention. Figure 7 The graph shows the test results of the phosphoric acid doping degree of the composite film prepared in an embodiment of the present invention. Figure 8 The image shows the durability test results of the composite membrane prepared in an embodiment of the present invention at 200°C. Figure 9 The figure shows the tensile properties test results of the composite membrane prepared in an embodiment of the present invention; Figure 10 The stress-strain curve of the composite membrane prepared in the embodiment of the present invention; Figure 11 The images shown are of the composite membranes prepared according to the embodiments of the present invention after being soaked in Fenton's reagent. a is Example 1, b is Example 2, c is Example 3, and d is Example 4. Detailed Implementation

[0023] To more clearly illustrate the purpose, technical solution, and advantages of this disclosure, the present invention will be further described below in conjunction with specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Any proportional adjustments or conventional substitutions made by those skilled in the art to the amount of raw materials, membrane size, reaction vessel specifications, and membrane laying method without departing from the essential content of the present invention should be included within the scope of protection of the present invention.

[0024] Unless otherwise specified, the raw materials used below, including phosphoric acid, phosphorus pentoxide, 3,3'-diaminobenzidine, 4,4'-dicarboxylic acid diphenyl ether, starch, and graphene oxide aqueous dispersion, are all commercially available. The concentration of the graphene oxide aqueous dispersion is 2 mg / mL.

[0025] Example 1: Preparation of Composite Membrane Samples The preparation process of the composite membrane sample is as follows: Figure 1 As shown.

[0026] (1) Preparation of polyphosphoric acid system containing graphene oxide and starch A graphene oxide aqueous dispersion was mixed with phosphorus pentoxide, wherein the molar ratio of phosphorus pentoxide to water in the graphene oxide aqueous dispersion was 1:3. The mixture was reacted at 70°C for 30 minutes to allow the phosphorus pentoxide and water to react and form a phosphoric acid system containing graphene oxide. Subsequently, 2.85 g of starch was added and mixed thoroughly to obtain a phosphoric acid system containing graphene oxide and starch.

[0027] The above-mentioned phosphoric acid system containing graphene oxide and starch was mixed with phosphorus pentoxide at a mass ratio of 1:1.4, heated to 120°C, and stirred at this temperature for 5 hours. After the phosphorus pentoxide was fully dissolved and a black homogeneous solution was formed, a polyphosphoric acid system containing graphene oxide and starch was obtained. The resulting reaction solution was transferred to a pre-dried, sealed glass container and stored for later use.

[0028] (2) In-situ polymerization reaction Under nitrogen protection, 5 mmol of 3,3'-diaminobenzidine and 5 mmol of 4,4'-dicarboxylic acid diphenyl ether were weighed and placed in a 100 mL three-necked flask. 20 mL of the polyphosphoric acid system containing graphene oxide and starch prepared in step (1) was added to the three-necked flask. The reaction system was heated to 90 °C and mechanically stirred for 1 hour, then heated to 150 °C and reacted for 8 hours, and then heated to 190 °C and reacted for 7 hours to obtain a hot slurry liquid.

[0029] (3) Direct film laying and drying The hot slurry obtained in step (2) was uniformly coated onto a clean glass plate preheated to 100°C. After coating, the glass plate was placed in a constant temperature and humidity chamber and allowed to stand for 14 days to form a film. During the standing process, polyphosphoric acid absorbed water and was converted into phosphoric acid within the membrane, while the slurry gradually solidified into a film. After the standing period, the membrane was peeled off from the glass plate, the liquid on the membrane surface was wiped off, and the membrane was dried under vacuum at 100°C for 24 hours to remove residual moisture, thus obtaining a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide.

[0030] Example 2: Preparation of Composite Membrane Samples The preparation process of the composite membrane sample is as follows: Figure 1 As shown.

[0031] (1) Preparation of polyphosphoric acid system containing graphene oxide and starch A graphene oxide aqueous dispersion was mixed with phosphorus pentoxide, wherein the molar ratio of phosphorus pentoxide to water in the graphene oxide aqueous dispersion was 1:3. The mixture was reacted at 70°C for 30 minutes to allow the phosphorus pentoxide and water to react and form a phosphoric acid system containing graphene oxide. Subsequently, 2.14 g of starch was added and mixed thoroughly to obtain a phosphoric acid system containing graphene oxide and starch.

[0032] The above-mentioned phosphoric acid system containing graphene oxide and starch was mixed with phosphorus pentoxide at a mass ratio of 1:1.4, heated to 120°C, and stirred at this temperature for 5 hours. After the phosphorus pentoxide was fully dissolved and a black homogeneous solution was formed, a polyphosphoric acid system containing graphene oxide and starch was obtained. The resulting reaction solution was transferred to a pre-dried, sealed glass container and stored for later use.

[0033] (2) In-situ polymerization reaction Under nitrogen protection, 5 mmol of 3,3'-diaminobenzidine and 5 mmol of 4,4'-dicarboxylic acid diphenyl ether were weighed and placed in a 100 mL three-necked flask. 20 mL of the polyphosphoric acid system containing graphene oxide and starch prepared in step (1) was added to the three-necked flask. The reaction system was heated to 90 °C and mechanically stirred for 1 hour, then heated to 150 °C and reacted for 8 hours, and then heated to 190 °C and reacted for 7 hours to obtain a hot slurry liquid.

[0034] (3) Direct film laying and drying The hot slurry obtained in step (2) was uniformly coated onto a clean glass plate preheated to 100°C. After coating, the glass plate was placed in a constant temperature and humidity chamber and allowed to stand for 14 days to form a film. During the standing process, polyphosphoric acid absorbed water and was converted into phosphoric acid within the membrane, while the slurry gradually solidified into a film. After the standing period, the membrane was peeled off from the glass plate, the liquid on the membrane surface was wiped off, and the membrane was dried under vacuum at 100°C for 24 hours to remove residual moisture, thus obtaining a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide.

[0035] Example 3: Preparation of Composite Membrane Samples The preparation process of the composite membrane sample is as follows: Figure 1 As shown.

[0036] (1) Preparation of polyphosphoric acid system containing graphene oxide and starch A graphene oxide aqueous dispersion was mixed with phosphorus pentoxide, wherein the molar ratio of phosphorus pentoxide to water in the graphene oxide aqueous dispersion was 1:3. The mixture was reacted at 70°C for 30 minutes to allow the phosphorus pentoxide and water to react and form a phosphoric acid system containing graphene oxide. Subsequently, 1.43 g of starch was added and mixed thoroughly to obtain a phosphoric acid system containing graphene oxide and starch.

[0037] The above-mentioned phosphoric acid system containing graphene oxide and starch was mixed with phosphorus pentoxide at a mass ratio of 1:1.4, heated to 120°C, and stirred at this temperature for 5 hours. After the phosphorus pentoxide was fully dissolved and a black homogeneous solution was formed, a polyphosphoric acid system containing graphene oxide and starch was obtained. The resulting reaction solution was transferred to a pre-dried, sealed glass container and stored for later use.

[0038] (2) In-situ polymerization reaction Under nitrogen protection, 5 mmol of 3,3'-diaminobenzidine and 5 mmol of 4,4'-dicarboxylic acid diphenyl ether were weighed and placed in a 100 mL three-necked flask. 20 mL of the polyphosphoric acid system containing graphene oxide and starch prepared in step (1) was added to the three-necked flask. The reaction system was heated to 90 °C and mechanically stirred for 1 hour, then heated to 150 °C and reacted for 8 hours, and then heated to 190 °C and reacted for 7 hours to obtain a hot slurry liquid.

[0039] (3) Direct film laying and drying The hot slurry obtained in step (2) was uniformly coated onto a clean glass plate preheated to 100°C. After coating, the glass plate was placed in a constant temperature and humidity chamber and allowed to stand for 14 days to form a film. During the standing process, polyphosphoric acid absorbed water and was converted into phosphoric acid within the membrane, while the slurry gradually solidified into a film. After the standing period, the membrane was peeled off from the glass plate, the liquid on the membrane surface was wiped off, and the membrane was dried under vacuum at 100°C for 24 hours to remove residual moisture, thus obtaining a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide.

[0040] Example 4: Preparation of Composite Membrane Samples The preparation process of the composite membrane sample is as follows: Figure 1 As shown.

[0041] (1) Preparation of polyphosphoric acid system containing graphene oxide and starch A graphene oxide aqueous dispersion was mixed with phosphorus pentoxide, wherein the molar ratio of phosphorus pentoxide to water in the graphene oxide aqueous dispersion was 1:3. The mixture was reacted at 70°C for 30 minutes to allow the phosphorus pentoxide and water to react and form a phosphoric acid system containing graphene oxide. Subsequently, 0.71 g of starch was added and mixed thoroughly to obtain a phosphoric acid system containing graphene oxide and starch.

[0042] The above-mentioned phosphoric acid system containing graphene oxide and starch was mixed with phosphorus pentoxide at a mass ratio of 1:1.4, heated to 120°C, and stirred at this temperature for 5 hours. After the phosphorus pentoxide was fully dissolved and a black homogeneous solution was formed, a polyphosphoric acid system containing graphene oxide and starch was obtained. The resulting reaction solution was transferred to a pre-dried, sealed glass container and stored for later use.

[0043] (2) In-situ polymerization reaction Under nitrogen protection, 5 mmol of 3,3'-diaminobenzidine and 5 mmol of 4,4'-dicarboxylic acid diphenyl ether were weighed and placed in a 100 mL three-necked flask. 20 mL of the polyphosphoric acid system containing graphene oxide and starch prepared in step (1) was added to the three-necked flask. The reaction system was heated to 90 °C and mechanically stirred for 1 hour, then heated to 150 °C and reacted for 8 hours, and then heated to 190 °C and reacted for 7 hours to obtain a hot slurry liquid.

[0044] (3) Direct film laying and drying The hot slurry obtained in step (2) was uniformly coated onto a clean glass plate preheated to 100°C. After coating, the glass plate was placed in a constant temperature and humidity chamber and allowed to stand for 14 days to form a film. During the standing process, polyphosphoric acid absorbed water and was converted into phosphoric acid within the membrane, while the slurry gradually solidified into a film. After the standing period, the membrane was peeled off from the glass plate, the liquid on the membrane surface was wiped off, and the membrane was dried under vacuum at 100°C for 24 hours to remove residual moisture, thus obtaining a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide.

[0045] Example 5: Infrared Spectroscopy Test of Composite Film The infrared spectra of the starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 are as follows: Figure 2 As shown. All composite membranes are at 2853 cm⁻¹. -1 1012 cm -1 A hydrogen bond characteristic peak appears at 3361 cm⁻¹. -1 The characteristic peak of starch hydroxyl (-OH) is at 1648 cm⁻¹. -1 1447 cm -1 The peak is a characteristic peak of the imidazole ring, at 1228 cm⁻¹. -1 The peaks represent characteristic ether bonds (COC). The intensity of the hydrogen bond characteristic peaks gradually increases with increasing starch content, indicating that in-situ polymerization allows starch to be distributed around OPBI. Hydrogen bonds can be formed between oxygen-containing groups such as hydroxyl groups (-OH), ether bonds (COC), and phosphate groups, promoting the formation of a hydrogen bond network and effectively improving proton conductivity.

[0046] Example 6 XRD test of composite film The XRD patterns of the starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 are as follows: Figure 3 As shown, all composite films exhibit amorphous broad peaks at 2θ = 20°-30°, without the characteristic crystalline peaks of starch. This indicates that the starch crystalline structure was destroyed during the in-situ polymerization process and uniformly dispersed in the OPBI matrix in an amorphous state. This amorphous characteristic is beneficial for the doping of phosphoric acid, thereby improving the proton conductivity of the composite film.

[0047] Example 7: TGA and DTG tests on the composite membrane The TGA and DTG of the starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 are as follows: Figure 4 and Figure 5 As shown, the thermogravimetric analysis (TGA) of the composite membrane can be divided into three stages: 100-200℃ is due to the evaporation of residual solvent and moisture. 300-400℃ is caused by thermal degradation of the starch backbone; because starch has low thermal stability, the weight loss becomes more pronounced as the proportion of starch increases. The TGA occurring above 550℃ can be attributed to the decomposition of the OPBI backbone structure. All composite membranes show no significant thermal decomposition below 220℃, fully meeting the requirements for high-temperature proton exchange membranes.

[0048] Example 8: Performance Testing of Composite Films (Phosphoric Acid Doping Degree and Proton Conductivity) The proton conductivity and phosphate doping degree of the starch and graphene oxide synergistic modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 are as follows: Figure 6 and Figure 7 As shown. Using acid-base titration, the phosphoric acid doping levels in Examples 1, 2, 3, and 4 were 9.08 mol H3PO4, 9.02 mol H3PO4, 9.72 mol H3PO4, and 9.02 mol H3PO4, respectively. The polyphosphoric acid within the membrane absorbs water and converts to phosphoric acid; therefore, the amount of adsorbed phosphoric acid varies little. The introduction of starch has a minimal impact on the phosphoric acid doping level, resulting in a uniform and stable phosphoric acid loading within the membrane. Gradient temperature tests were conducted under anhydrous conditions. At 160℃, the proton conductivity of Example 1 reached 0.224 S cm⁻¹. -1 At 180℃, it is 0.256 S cm. -1 At 240℃, it reaches as high as 0.354 Scm. -1 This is attributed to the abundant oxygen-containing groups in the composite membrane enhancing its proton conductivity through a hydrogen bond network formed by starch. The abundant oxygen-containing groups in the starch skeletal structure of the membrane can construct such a dense hydrogen bond network. This dense hydrogen bond network effectively maintains H3PO4, and the abundant oxygen-containing groups in the polymer chain remain stable at high temperatures. Therefore, in-situ polymerization and the addition of starch with oxygen-containing groups can increase the hydrogen bonds between the polymer and phosphoric acid, thereby improving the membrane's proton conductivity.

[0049] Example 9: Durability Test of Composite Membrane The durability of the starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 is as follows: Figure 8As shown, after a long-term test at 200°C in an anhydrous environment for 600 min, the proton conductivity of Examples 1 and 2 remained at 0.150 S cm⁻¹. -1 All samples showed a conductivity consistently higher than 0.1 S cm⁻¹. -1 This is because the composite membrane primarily constructs proton conduction pathways within the hydrogen bond network of oxygen-containing starch groups, exhibiting less dependence on phosphate molecules and demonstrating excellent stability. The H3PO4 molecules in the composite membrane are formed by polyphosphoric acid absorbing water within the membrane to create phosphate, thus allowing for tight integration into the hydrogen bond network and resulting in excellent phosphate retention.

[0050] Example 10 Tensile strength test of composite membrane The tensile strength of the starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 is as follows: Figure 9 and Figure 10 As shown, the tensile strength gradually increases with increasing starch content, with Example 1 exhibiting the best tensile strength. In-situ polymerization enables the starch oxygen-containing groups to form dense hydrogen bonds with the OPBI chains, enhancing the inter-chain forces of the polymer. The membrane mechanical strength meets the requirements for fuel cell assembly and long-term operation.

[0051] Example 11 Oxidation stability test of composite membrane The starch- and graphene oxide-modified polybenzimidazole high-temperature proton exchange membranes prepared in Examples 1-4 were placed in Fenton's reagent (3% H2O2, 4 ppm Fe). 2+ Soak in water at room temperature for 120 hours. (For example...) Figure 11 As shown, the membrane remains intact and unbroken. The hydrogen bond network constructed from starch can resist the erosion of oxidative free radicals, giving the composite membrane excellent oxidation resistance and making it suitable for the harsh working environment inside fuel cells.

[0052] The embodiments described above are merely preferred embodiments of the present invention, and not all possible embodiments of the present invention. For those skilled in the art, any equivalent substitutions, simple modifications, or parameter adjustments made to the present invention without departing from its principles and essence should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature proton exchange membrane of polybenzimidazole synergistically modified with starch and graphene oxide, characterized in that, Includes the following steps: 1) Preparation of polyphosphoric acid containing graphene oxide and starch: Aqueous dispersion of graphene oxide is mixed with phosphorus pentoxide, and the phosphorus pentoxide reacts with water in the aqueous dispersion of graphene oxide. After the reaction is carried out under heating conditions, starch is added to obtain a phosphoric acid system containing graphene oxide and starch. The phosphoric acid system containing graphene oxide and starch is then mixed with phosphorus pentoxide and heated and stirred until a homogeneous solution is formed to obtain polyphosphoric acid containing graphene oxide and starch. 2) In-situ polymerization reaction: Under nitrogen protection, 3,3'-diaminobenzidine and 4,4'-dicarboxylic acid diphenyl ether are added to the polyphosphoric acid system containing graphene oxide and starch obtained in step 1), and a segmented heating in-situ polymerization reaction is carried out to obtain a hot slurry liquid. 3) Direct membrane deposition and post-treatment: The hot slurry liquid obtained in step 2) is coated onto a preheated glass plate and allowed to stand in a constant temperature and humidity chamber to form a membrane; after membrane formation, the membrane is peeled off from the glass plate, the liquid on the membrane surface is removed, and vacuum drying is performed to obtain a polybenzimidazole high-temperature proton exchange membrane synergistically modified with starch and graphene oxide.

2. The preparation method according to claim 1, characterized in that, In step 1), the concentration of the graphene oxide aqueous dispersion is 1 mg / mL to 4 mg / mL; phosphorus pentoxide is mixed with water in the graphene oxide aqueous dispersion at a molar ratio of 1:(2 to 5) and reacted at 60℃ to 100℃ for 0.5h to 1h.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1), the starch accounts for 1wt% to 5wt% of the solid content; the phosphoric acid system containing graphene oxide and starch is mixed with phosphorus pentoxide at a mass ratio of 1:(1 to 2) and stirred at 100℃ to 120℃ for 4h to 6h.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step 2), the molar ratio of 3,3'-diaminobenzidine to 4,4'-dicarboxylic diphenyl ether is 1:1; the total solid content of 3,3'-diaminobenzidine and 4,4'-dicarboxylic diphenyl ether in the reaction system is 1.5 w / v% to 15 w / v.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step 2), the segmented heating in-situ polymerization reaction includes: first, mechanical stirring at 70℃~120℃ for 0.5h~2h, then heating to 140℃~170℃ for 5h~10h, and then heating to 180℃~200℃ for 8h~10h.

6. The preparation method according to any one of claims 1 to 5, characterized in that, In step 3), the preheating temperature of the glass plate is 80℃~100℃, the temperature of the constant temperature and humidity chamber is 25℃~35℃, the humidity is 45%~85%, and the static film formation time is 3~21 days.

7. The preparation method according to any one of claims 1 to 6, characterized in that, In step 3), the vacuum drying temperature is 80℃~120℃ and the vacuum drying time is 12h~36h.

8. The preparation method according to claim 1, characterized in that, In step 1), the concentration of the graphene oxide aqueous dispersion is 2 mg / mL to 3 mg / mL, the molar ratio of phosphorus pentoxide to water in the graphene oxide aqueous dispersion is 1:(3-4), and the reaction is carried out at 80°C for 0.8 h; the starch content is 2wt% to 4wt%, and the phosphoric acid system containing graphene oxide and starch is mixed with phosphorus pentoxide at a mass ratio of 1:(1.2-1.8), and stirred at 110°C for 5 h.

9. A high-temperature proton exchange membrane of polybenzimidazole synergistically modified with starch and graphene oxide, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the starch and graphene oxide synergistically modified polybenzimidazole high-temperature proton exchange membrane according to claim 9 in the field of proton exchange membrane fuel cells.

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