A ternary block copolymer polybenzimidazole, a high-temperature proton exchange membrane and a preparation method thereof

Abstract

The present invention provides a ternary block copolymer polybenzimidazole, a high-temperature proton exchange membrane and a preparation method thereof. A polymerization reaction is carried out using an OPBI prepolymer with a carboxyl end group, an F6-PBI prepolymer with a carboxyl end group and an m-PBI prepolymer with a diamino end group to obtain the ternary block copolymer polybenzimidazole. The ternary block copolymer polybenzimidazole powder is dissolved in a polar aprotic organic solvent to obtain a copolymer solution, which is formed into a film on a flat plate. After the solvent evaporates, a ternary block copolymer film is obtained. The ternary block copolymer dry film is impregnated in phosphoric acid to obtain a ternary block copolymer wet film, i.e., a high-temperature proton exchange membrane of the ternary block copolymer polybenzimidazole. Compared with traditional PBI membrane materials, the high-temperature proton exchange membrane of the ternary block copolymer polybenzimidazole has better proton conduction ability, antioxidant property and film-forming property, and has good application prospects in the field of high-temperature proton exchange membrane fuel cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of polybenzimidazole materials for polymers and high-temperature proton exchange membrane fuel cells, and particularly relates to a triblock copolymerized polybenzimidazole, a high-temperature proton exchange membrane, and a preparation method thereof. Background Art

[0002] High-temperature proton exchange membrane fuel cells (HT-PEMFCs) operate at high temperatures (generally 120°C - 180°C), have no liquid water during the reaction process and do not require humidification, have simple water and heat management, strong resistance to CO poisoning, and can use reformed gases such as formic acid and methanol for direct feeding, effectively solving the hydrogen source problem faced by low-temperature proton exchange membrane fuel cells (LT-PEMFCs). Currently, it has become a research hotspot in the industry. Among them, phosphoric acid (PA)-doped polybenzimidazole (PBI) electrolyte membranes are widely used in HT-PEMFCs due to their high proton conductivity, good chemical stability, and low cost under high-temperature non-humidification conditions. In order to further improve their performance and stability, researchers have modified the PA-PBI system through methods such as crosslinking, doping, and grafting.

[0003] Block copolymerization, as a modification method for molecular main chain design, is often used in the modification of new polymer materials, and can simultaneously exert the advantages of each polymer in the block copolymer, effectively improving the various properties of the polymer. Currently, in various studies, there are binary block copolymer studies on m-PBI, OPBI, p-PBI, py-PBI, etc. These binary block copolymers all exhibit better performance and stability than pure PBI. Among them, the microphase separation structure generated due to the different rigidities of each PBI segment can enhance the proton conduction and phosphoric acid retention ability in the electrolyte film after doping with phosphoric acid. Although binary block copolymerized PBI materials have received the attention of researchers, triblock copolymerized PBI materials are still rarely studied. Summary of the Invention

[0004] In order to overcome the deficiencies in the prior art, the inventor of the present invention has conducted intensive research and provided a triblock copolymerized polybenzimidazole, a high-temperature proton exchange membrane, and a preparation method thereof. This triblock copolymerized polybenzimidazole uses m-polybenzimidazole (m-PBI), polybenzimidazole containing ether bonds (OPBI), and hexafluoroisopropyl polybenzimidazole (F6-PBI) as copolymer units. The formed high-temperature proton exchange membrane has better proton conduction ability, antioxidant property, and film-forming property compared with traditional PBI membrane materials, and has good application prospects in the field of high-temperature proton exchange membrane fuel cells.

[0005] The technical solutions provided by the present invention are as follows:

[0006] In the first aspect, a triblock copolymerized polybenzimidazole has the following structure:

[0007]

[0008] Among them, X is the molar percentage of the polyether-linked polybenzimidazole (OPBI) block in the total molecular weight, which is 0.15 - 0.35; Y is the molar percentage of the hexafluoroisopropyl polybenzimidazole (F6-PBI) block in the total molecular weight, which is 0.15 - 0.35; Z is the molar percentage of the m-polybenzimidazole (m-PBI) block in the total molecular weight, satisfying 1 - X - Y.

[0009] In a second aspect, a preparation method of a ternary block copolymer polybenzimidazole includes: performing a polymerization reaction on an OPBI prepolymer with a carboxyl end group, an F6-PBI prepolymer with a carboxyl end group, and an m-PBI prepolymer with a diamino end group at 180 - 200 °C to obtain the ternary block copolymer polybenzimidazole.

[0010] Further, the OPBI prepolymer with a carboxyl end group is obtained by the following method: reacting and polymerizing 4,4'-dicarboxydiphenyl ether (OBBA) with 3,3'-diaminobenzidine (DAB), such as reacting and polymerizing at 140 - 160 °C for 2 - 4 h; preferably, OBBA:DAB = (1.04 - 1.08):1, and 4% - 8% excess OBBA is used for end-group modification.

[0011] Further, the F6-PBI prepolymer with a carboxyl end group is obtained by the following method: reacting and polymerizing 2,2-bis(4-carboxyphenyl)hexafluoropropane (CBHF) with 3,3'-diaminobenzidine (DAB), such as reacting and polymerizing at 190 - 210 °C for 10 - 14 h; preferably, CBHF:DAB = (1.04 - 1.08):1, and 4% - 8% excess CBHF is used for end-group modification.

[0012] Further, the m-PBI prepolymer with a diamino end group is obtained by the following method: reacting and polymerizing isophthalic acid (IPA) with 3,3'-diaminobenzidine (DAB), such as reacting and polymerizing at 180 - 190 °C for 10 - 12 h; preferably, IPA:DAB = 1:(1.04 - 1.08), and 4% - 8% excess DAB is used for end-group modification.

[0013] Further, the reaction system of the ternary block copolymer polybenzimidazole uses polyphosphoric acid (PPA) or Eaton's reagent as a solvent and a catalyst; the reaction system of the OPBI prepolymer with a carboxyl end group uses polyphosphoric acid (PPA) or Eaton's reagent as a solvent and a catalyst; the reaction system of the F6-PBI prepolymer with a carboxyl end group uses polyphosphoric acid (PPA) or Eaton's reagent as a solvent and a catalyst; the reaction system of the m-PBI prepolymer with a diamino end group uses polyphosphoric acid (PPA) or Eaton's reagent as a solvent and a catalyst.

[0014] Further, the preparation method further includes a post-reaction treatment step: after the polymerization reaction is completed, the polymer solution is poured into a beaker containing deionized water, and filamentous solids precipitate out. It is neutralized to neutral with a weak alkaline solution, and then the solid is washed several times, ground into powder and dried to obtain block copolymer powder.

[0015] In a third aspect, a ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane uses the ternary block copolymerized polybenzimidazole described in the first aspect as a membrane material, or the ternary block copolymerized polybenzimidazole prepared by the preparation method described in the second aspect as a membrane material. The ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane uses phosphoric acid as a proton carrier.

[0016] In a fourth aspect, a preparation method of a ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane includes the following steps: dissolving the ternary block copolymerized polybenzimidazole powder in a polar aprotic organic solvent to obtain a copolymer solution, forming a film on a flat plate, and obtaining a ternary block copolymer thin film after the solvent evaporates;

[0017] Immerse the dry film of the ternary block copolymer in phosphoric acid to obtain a wet film of the ternary block copolymer.

[0018] Further, the polar aprotic solvent is at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone or dimethyl sulfoxide; the thickness of the copolymer solution for film formation is 1100±200 microns, and the thickness after drying is 50±10 microns.

[0019] In a fifth aspect, a high-temperature proton exchange membrane fuel cell uses the ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane described in the third aspect as a battery separator, or the ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane prepared by the preparation method described in the fourth aspect as a battery separator.

[0020] A ternary block copolymerized polybenzimidazole, a high-temperature proton exchange membrane and a preparation method thereof provided by the present invention have the following beneficial effects:

[0021] By means of a block copolymerization method, the present invention copolymerizes m-PBI, OPBI, and F6-PBI prepolymers, so that the ternary block copolymer simultaneously has the high thermal stability and mechanical stability of m-PBI, the easy solubility and high film-forming property of OPBI, and the high antioxidant stability of F6-PBI, making up for the shortcomings and deficiencies of each polymer. Compared with random copolymerization, block copolymerization shows a phase separation structure at the microscopic level, and this structure can effectively promote proton conduction and improve the phosphoric acid retention ability, thereby improving the proton conductivity and phosphoric acid retention ability of the ternary block copolymerized high-temperature proton exchange membrane. Description of the Drawings

[0022] Figure 1It is the Fenton test chart of antioxidant properties of the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1-3 and the commercialized polybenzimidazole membrane;

[0023] Figure 2 It is the thermogravimetric analysis chart of the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1-3 and the commercialized polybenzimidazole membrane;

[0024] Figure 3 It is the proton conductivity of the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1-3 under non-humidifying conditions at different phosphoric acid doping amounts in the range of 80-160 °C;

[0025] Figure 4 It is the comparison chart of H2 / Air battery performance of the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1-3 and the commercialized polybenzimidazole membrane under non-humidifying conditions at 160 °C. Detailed implementation manners

[0026] The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and more definite with these descriptions.

[0027] The special term "exemplary" here means "serving as an example, an embodiment or illustrative". Any embodiment described as "exemplary" here does not have to be interpreted as superior to or better than other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings do not have to be drawn to scale unless otherwise specified.

[0028] The present invention provides a triblock copolymerized polybenzimidazole, and the structure is as follows:

[0029]

[0030] Among them, X is the molar percentage of the polybenzimidazole with ether bond (OPBI) block in the total molecular weight, preferably 0.15-0.35, Y is the molar percentage of the polybenzimidazole with hexafluoroisopropyl group (F6-PBI) block in the total molecular weight, preferably 0.15-0.35, and Z is the molar percentage of the polybenzimidazole with meta-group (m-PBI) block in the total molecular weight, satisfying 1-X-Y.

[0031] m-PBI, as the only commercially available PBI material, has advantages such as good thermal stability and high mechanical strength. However, its overly rigid main-chain structure results in poor solubility and film-forming properties, and its proton conductivity is also low after doping with phosphoric acid. The flexible ether bonds in the main chain molecules of OPBI significantly enhance the solubility and film-forming properties of the polymer, and its proton conductivity is relatively high after doping with phosphoric acid. However, the thermal stability and mechanical properties of OPBI are inferior to those of m-PBI. The chain segment rigidity and mechanical strength of F6-PBI are between those of m-PBI and OPBI, and it has excellent thermal stability and antioxidant ability, but the cost is relatively high. The inventors of the present invention use m-PBI, OPBI, and F6-PBI as copolymer units, and the formed high-temperature proton exchange membrane has better proton conduction ability, antioxidant property, and film-forming property compared with traditional PBI membrane materials.

[0032] The molar molecular weight of the triblock copolymerized polybenzimidazole is 10,000 - 20,000 g / mol, and the intrinsic viscosity is 0.8 - 1.2 dL / g.

[0033] The triblock copolymerized polybenzimidazole can be used to prepare high-temperature proton exchange membranes and is applied to high-temperature proton exchange membrane fuel cells.

[0034] The preparation process of the above triblock copolymerized polybenzimidazole and its membrane material is shown in Formula 1. The synthesis process is carried out in an inert atmosphere. Using OPBI prepolymer with a carboxyl end group (OPBI-Ac), F6-PBI prepolymer with a carboxyl end group (F6-PBI-Ac), and m-PBI prepolymer with a diamino end group (m-PBI-Am) in polyphosphoric acid (PPA) or Eaton's reagent (a mixed reagent of phosphorus pentoxide and methanesulfonic acid), the polymerization reaction is carried out at 180 - 200 °C, such as 190 °C.

[0035]

[0036] The synthesis steps of the OPBI prepolymer OPBI-Ac with a carboxyl end group are shown in Formula 2. It is obtained by reacting 4,4'-dicarboxydiphenyl ether (OBBA) with 3,3'-diaminobenzidine (3,3'-DAB) in a system using PPA or Eaton's reagent as a solvent and catalyst at 140 - 160 °C for 2 - 4 h. Among them, OBBA:DAB = (1.04 - 1.08):1, and 4% - 8% excess OBBA is used for end-group modification. The molar molecular weight of OPBI-Ac is 2,000 - 4,000 g / mol, and the intrinsic viscosity is 0.4 - 0.6 dL / g. Ac represents that its end group is a carboxyl group.

[0037]

[0038] The synthesis steps of the F6-PBI prepolymer F6-PBI-Ac with a carboxyl end group are shown in Equation 3. It is obtained by reacting 2,2-bis(4-carboxyphenyl)hexafluoropropane (CBHF) with DAB in a system using PPA or Eaton's reagent as the solvent and catalyst at 190 - 210 °C for 10 - 14 h, where CBHF:DAB = (1.04 - 1.08):1, and 4% - 8% excess CBHF is used for end group modification. The molar molecular weight of F6-PBI-Ac is 2000 - 4000 g / mol, and the intrinsic viscosity is 0.4 - 0.6 dL / g. Ac represents that its end group is a carboxyl group.

[0039]

[0040] The synthesis steps of the m-PBI prepolymer m-PBI-Am with an amino end group are shown in Equation 4. It is obtained by reacting isophthalic acid (IPA) with DAB in a system using PPA or Eaton's reagent as the solvent and catalyst at 180 - 190 °C for 10 - 12 h, where IPA:DAB = 1:(1.04 - 1.08), and 4% - 8% excess DAB is used for end group modification. The number average molecular weight of m-PBI-Am is 2000 - 4000 g / mol, and the intrinsic viscosity is 0.4 - 0.6 dL / g. Am represents that its end group is an amino group.

[0041]

[0042] The ternary block copolymer is based on the above three prepolymers, and the composition of the copolymer is adjusted by changing the molar ratio of the repeating units of each prepolymer. For example, X:Y:Z = 0.15:0.35:0.5, 0.25:0.25:0.5, 0.35:0.15:0.5. The block copolymers with these three different ratios are named m0.5-O0.15-F0.35, m0.5-O0.25-F0.25, and m0.5-O0.35-F0.15 respectively.

[0043] Considering the process reaction rate and operability, in a system using PPA or Eaton's reagent as the reaction solvent and catalyst, the total mass fraction of the reactants is 3.5 wt% - 5 wt%.

[0044] After copolymerization is completed in a PPA solution or Eaton's reagent, the resulting reactant solution is poured into a container filled with deionized water, and a solid precipitates. The solid is rinsed several times with deionized water and then neutralized to neutrality with a weakly basic solution such as saturated sodium bicarbonate solution or ammonia water. The solid is then washed several times with methanol or ethanol and deionized water, placed in a vacuum oven at 60 - 80 °C for drying (for example, for more than 3 days), and ground into powder to obtain the triblock copolymer powder.

[0045] The copolymer powder is dissolved in a polar aprotic organic solvent under heating conditions of 60 - 100 °C to prepare a 5 - 10 wt% copolymer solution, which is cast into a film on a polytetrafluoroethylene plate or a glass plate, and placed in an oven at 60 - 80 °C for drying for more than 12 h. After the solvent evaporates, a dry triblock copolymer film is obtained. Preferably, the polar aprotic solvent is at least one of N,N - dimethylacetamide (DAMc), N,N - dimethylformamide (DMF), N - methylpyrrolidone (NMP), or dimethyl sulfoxide (DMSO). Preferably, the thickness of the copolymer solution cast into a film on the plate is 1100 ± 200 microns, and the thickness after drying is 50 ± 10 microns.

[0046] The dry triblock copolymer film is immersed in phosphoric acid to obtain a wet triblock copolymer film, that is, a triblock copolymer polybenzimidazole proton exchange membrane; specifically: it is soaked in 80% - 85% mass fraction phosphoric acid in an oven environment at 20 - 40 °C for 0.5 - 1 h, then the temperature is raised to 60 - 80 °C and soaked for 3 - 4 h, and then the temperature is raised to 100 - 120 °C and soaked for 10 h - 20 h to allow the triblock polybenzimidazole membrane material to fully absorb phosphoric acid. Of course, the immersion method is not limited to the above one, as long as the requirements of sufficient immersion and flatness after immersion are met.

[0047] Example

[0048] Preparation of Three Prepolymers of Phosphoric Acid-Doped Ternary Block Copolymer High-Temperature Proton Exchange Membrane Materials

[0049] m - PBI - Am: Weigh 2.22 g of m - dibenzoic acid (13.38 mmol) and 3.038 g of 3,3’ - diaminobenzidine (14.18 mmol), add them to a three - necked flask containing 100 g of PPA, introduce nitrogen for protection, and use mechanical stirring to uniformly mix the raw materials at 100 °C, then raise the temperature to 190 °C and react for 12 h. Pour the completed reaction solution into a beaker filled with a large amount of deionized water, and a filamentous solid precipitates. Wash the solid several times with deionized water, add saturated sodium bicarbonate solution to neutralize to pH = 7. Then wash the solid several times with deionized water and methanol, place it in a vacuum oven at 60 °C for drying for 3 days to obtain the m - PBI - Am prepolymer powder, with a molar molecular weight of 3100 g / mol and an intrinsic viscosity of 0.56 dL / g.

[0050] OPBI-Ac: Weigh 2.951 g of 4,4'-dicarboxydiphenyl ether (11.43 mmol) and 2.309 g of 3,3'-diaminobenzidine (10.78 mmol), add them to a three-necked flask containing 100 g of PPA, introduce nitrogen for protection, and use mechanical stirring to uniformly mix the raw materials at 100 °C. Then, raise the temperature to 140 °C and react for 4 h. Pour the completed reaction solution into a beaker containing a large amount of deionized water. Filamentous solids will precipitate. Wash the solids several times with deionized water, add saturated sodium bicarbonate solution to neutralize to pH = 7. Wash the solids several times with deionized water and methanol again, and place them in a vacuum oven at 60 °C for drying for 3 days to obtain OPBI-Ac prepolymer powder with a molar molecular weight of 3130 g / mol and an intrinsic viscosity of 0.41 dL / g.

[0051] F6-PBI-Ac: Weigh 4.124 g of 2,2-bis(4-carboxyphenyl)hexafluoropropane (10.51 mmol) and 2.125 g of 3,3'-diaminobenzidine (9.92 mmol), add them to a three-necked flask containing 100 g of PPA, introduce nitrogen for protection, and use mechanical stirring to uniformly mix the raw materials at 100 °C. Then, raise the temperature to 200 °C and react for 12 h. Pour the completed reaction solution into a beaker containing a large amount of deionized water. Filamentous solids will precipitate. Wash the solids several times with deionized water, add saturated sodium bicarbonate solution to neutralize to pH = 7. Wash the solids several times with deionized water and methanol again, and place them in a vacuum oven at 60 °C for drying for 3 days to obtain F6-PBI prepolymer powder with a molar molecular weight of 3110 g / mol and an intrinsic viscosity of 0.43 dL / g.

[0052] Preparation of m0.5-O0.25-F0.25, a Phosphoric Acid-Doped Ternary Block Copolymer High-Temperature Proton Exchange Membrane Material in Example 1 Preparation

[0053] Weigh 2.392 g of m-PBI-Am (7.766 mmol) prepolymer, 1.553 g of OPBI-Ac (3.883 mmol), and 2.074 g of F6-PBI-Ac (3.883 mmol), add them to a three-necked flask containing 100 g of PPA, introduce nitrogen for protection, and use mechanical stirring to uniformly mix the raw materials at 100 °C. Then, raise the temperature to 190 °C and react for 12 h. Pour the completed reaction solution into a beaker containing a large amount of deionized water. Filamentous solids will precipitate. Wash the solids several times with deionized water, add saturated sodium bicarbonate solution to neutralize to pH = 7. Wash the solids several times with deionized water and methanol again, and place them in a vacuum oven at 60 °C for drying for 3 days to obtain the triblock copolymer m0.5-O0.25-F0.25. Grind it into powder, dissolve it in the solvent NMP after drying, form a film with a thickness of 1100 microns, and after drying, the thickness is 50 microns. Immerse it in 85 wt% phosphoric acid. First, soak it in an oven environment at 30 °C for 0.5 h, then raise the temperature to 80 °C and soak for 3 h, and then raise the temperature to 120 °C and soak for 20 h to obtain a phosphoric acid-doped triblock copolymer high-temperature proton exchange membrane with a molar molecular weight of 16100 g / mol and an intrinsic viscosity of 1.62 dL / g.

[0054] Preparation of m0.5-O0.35-F0.15, a Phosphoric Acid-Doped Ternary Block Copolymer High-Temperature Proton Exchange Membrane Material in Example 2 Preparation

[0055] Weigh 2.392 g of m-PBI-Am (7.766 mmol) prepolymer, 2.177 g of OPBI-Ac (5.436 mmol), and 1.245 g of F6-PBI-Ac (2.330 mmol), add them to a three-necked flask containing 100 g of PPA, introduce nitrogen for protection, and use mechanical stirring to uniformly mix the raw materials at 100 °C. Then, raise the temperature to 190 °C and react for 12 h. Pour the completed reaction solution into a beaker containing a large amount of deionized water. Filamentous solids will precipitate. Wash the solids several times with deionized water, add saturated sodium bicarbonate solution to neutralize to pH = 7. Wash the solids several times with deionized water and methanol again, and place them in a vacuum oven at 60 °C for drying for 3 days to obtain the triblock copolymer m0.5-O0.35-F0.15. Grind it into powder, dissolve it in the solvent NMP after drying, form a film with a thickness of 1100 microns, and after drying, the thickness is 50 microns. Immerse it in 85 wt% phosphoric acid. First, soak it in an oven environment at 30 °C for 0.5 h, then raise the temperature to 80 °C and soak for 3 h, and then raise the temperature to 120 °C and soak for 20 h to obtain a phosphoric acid-doped triblock copolymer high-temperature proton exchange membrane with a molar molecular weight of 14300 g / mol and an intrinsic viscosity of 1.42 dL / g.

[0056] Preparation of m0.5-O0.15-F0.35, a Phosphoric Acid-Doped Ternary Block Copolymer High-Temperature Proton Exchange Membrane Material in Example 3 Preparation

[0057] Weigh 2.392 g of m-PBI-Am (7.766 mmol) prepolymer, 0.933 g of OPBI-Ac (2.330 mmol), and 2.905 g of F6-PBI-Ac (5.436 mmol) and add them to a three-necked flask containing 100 g of PPA. Introduce nitrogen for protection and use mechanical stirring to uniformly mix the raw materials at 100 °C. Then raise the temperature to 190 °C and react for 12 h. Pour the completed reaction solution into a beaker containing a large amount of deionized water. Filamentous solids will precipitate. Wash the solids several times with deionized water, and add saturated sodium bicarbonate solution to neutralize to pH = 7. Wash the solids several times with deionized water and methanol, and place them in a vacuum oven at 60 °C for drying for 3 days to obtain the triblock copolymer m0.5-O0.15-F0.35. Grind it into powder, dissolve it in the solvent NMP after drying, form a film with a thickness of 1100 microns, and after drying, the thickness is 50 microns. Immerse it in 85 wt% phosphoric acid. First, soak it in an oven environment at 30 °C for 0.5 h, then raise the temperature to 80 °C and soak for 3 h, and then raise the temperature to 120 °C and soak for 20 h to obtain a phosphoric acid-doped triblock copolymer high-temperature proton exchange membrane with a molar molecular weight of 16900 g / mol and an intrinsic viscosity of 1.71 dL / g.

[0058] The Fenton test diagrams of the antioxidant properties of the triblock copolymer polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1 to 3 and the commercial polybenzimidazole membrane are as Figure 1 shown. It can be seen that the antioxidant stability of the triblock copolymer proton exchange membrane is significantly improved compared to OPBI, and it is enhanced with the increase of the F6-PBI content in the block copolymer. Among them, the m0.5-O0.15-F0.35 membrane with the highest antioxidant stability has a mass loss of only 11.8% after 96 h of testing, while the mass loss of OPBI reaches 32.6%.

[0059] The thermogravimetric analysis diagrams of the triblock copolymer polybenzimidazole high-temperature proton exchange membrane materials obtained in Examples 1 to 3 and the commercial polybenzimidazole membrane are as Figure 2 shown. It can be seen that the thermal stability of the triblock copolymer is improved compared to OPBI. Among them, the thermal stability increases with the increase of the F6-PBI content. Among them, pure OPBI and the m0.5-O0.35-F0.15 membrane start to decompose at 200 °C, while the m0.5-O0.25-F0.25 and m0.5-O0.15-F0.35 membranes can maintain structural stability before 300 °C.

[0060] The proton conductivities of the triblock copolymer polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1 to 3 under different phosphoric acid doping amounts without humidification in the range of 80 - 160 °C are as Figure 3As shown, it can be seen that the proton conductivity of all high-temperature proton exchange membranes increases with the increase of temperature. Among them, the proton conductivity of the m0.5-O0.25-F0.25 triblock copolymer is the highest, reaching 161 mS / cm at 200 °C.

[0061] The comparison chart of the performance of the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane materials prepared in Examples 1-3 and the commercialized polybenzimidazole membrane in the H2 / Air battery under the condition of no humidification at 160 °C is as Figure 4 shown. It can be seen that the performance of the triblock copolymer high-temperature proton exchange membrane in the single cell is higher than that of the pure OPBI membrane, which is mainly reflected in the reduction of ohmic polarization. Among the triblock copolymer high-temperature proton exchange membranes, the m0.5-O0.25-F0.25 membrane has the best performance. At a current density of 0.5 A / cm 2 , its discharge voltage is increased by 68 mV compared with the pure OPBI membrane.

[0062] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions of the present invention and their implementation manners, and all of these fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

[0063] The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A ternary block copolymerized polybenzimidazole, characterized in that, The structure is as follows: Among them, X is the molar percentage of the polyether-containing polybenzimidazole OPBI block in the total molecular weight, which is 0.15 - 0.35, Y is the molar percentage of the hexafluoroisopropyl polybenzimidazole F6-PBI block in the total molecular weight, which is 0.15 - 0.35, and Z is the molar percentage of the m-polybenzimidazole m-PBI block in the total molecular weight, satisfying 1 - X - Y.

2. The preparation method of the triblock copolymerized polybenzimidazole according to claim 1, characterized in that, It includes: Using an OPBI prepolymer with a carboxyl end group, an F6-PBI prepolymer with a carboxyl end group, and an m-PBI prepolymer with a diamino end group to carry out a polymerization reaction at 180 - 200 °C to obtain a ternary block copolymerized polybenzimidazole.

3. The preparation method of the triblock copolymerized polybenzimidazole according to claim 2, characterized in that, The OPBI prepolymer with a carboxyl end group is prepared by the following method: Reacting and polymerizing 4,4'-dicarboxydiphenyl ether OBBA with 3,3'-diaminobenzidine DAB.

4. The preparation method of the triblock copolymerized polybenzimidazole according to claim 3, characterized in that, OBBA:DAB = (1.04 - 1.08):1, and 4% - 8% excess OBBA is used for end group modification.

5. The preparation method of the triblock copolymerized polybenzimidazole according to claim 2, characterized in that, The F6-PBI prepolymer with a carboxyl end group is prepared by the following method: Reacting and polymerizing 2,2-bis(4-carboxyphenyl)hexafluoropropane CBHF with 3,3'-diaminobenzidine DAB.

6. The preparation method of the triblock copolymerized polybenzimidazole according to claim 5, characterized in that, CBHF:DAB = (1.04 - 1.08):1, and 4% - 8% excess CBHF is used for end group modification.

7. The preparation method of the triblock copolymerized polybenzimidazole according to claim 2, characterized in that, The m-PBI prepolymer with a diamino end group is prepared by the following method: Reacting and polymerizing isophthalic acid IPA with 3,3'-diaminobenzidine DAB.

8. The preparation method of the triblock copolymerized polybenzimidazole according to claim 7, characterized in that, IPA:DAB = 1:(1.04 - 1.08), and 4% - 8% excess DAB is used for end group modification.

9. The preparation method of the triblock copolymerized polybenzimidazole according to any one of claims 2 to 8, characterized in that, The reaction system of the ternary block copolymerized polybenzimidazole uses polyphosphoric acid PPA or Eaton's reagent as a solvent and catalyst; and / or The reaction system of the OPBI prepolymer with a carboxyl end group uses polyphosphoric acid PPA or Eaton's reagent as a solvent and catalyst; and / or The reaction system of the F6-PBI prepolymer with a carboxyl end group uses polyphosphoric acid PPA or Eaton's reagent as a solvent and catalyst; and / or The reaction system of the m-PBI prepolymer with a diamino end group uses polyphosphoric acid PPA or Eaton's reagent as a solvent and catalyst.

10. The preparation method of the triblock copolymerized polybenzimidazole according to claim 2, wherein, The preparation method further includes a post-treatment step after the reaction: After the polymerization reaction is completed, pour the polymer solution into a beaker containing deionized water, and filamentous solids will precipitate. Neutralize it to neutral with a weak alkaline solution, then wash the solids several times, dry and grind to obtain block copolymer powder.

11. A ternary block copolymer polybenzimidazole high-temperature proton exchange membrane, characterized in that, Using the ternary block copolymerized polybenzimidazole described in claim 1 as a membrane material, or using the ternary block copolymerized polybenzimidazole prepared by the preparation method described in any one of claims 2 to 10 as a membrane material.

12. A ternary block copolymer polybenzimidazole high-temperature proton exchange membrane according to claim 11, characterized in that, The ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane uses phosphoric acid as a proton carrier.

13. A method for preparing a ternary block copolymer polybenzimidazole high-temperature proton exchange membrane according to claim 11 or 12, characterized in that, It includes the following steps: Dissolve the ternary block copolymerized polybenzimidazole powder in a polar aprotic organic solvent to obtain a copolymer solution, form a film on a flat plate, and obtain a ternary block copolymer film after the solvent evaporates; Immerse the ternary block copolymer dry film in phosphoric acid to obtain a ternary block copolymer wet film.

14. The preparation method of the ternary block copolymerized polybenzimidazole high-temperature proton exchange membrane according to claim 13, characterized in that, The polar aprotic organic solvent is at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone or dimethyl sulfoxide.

15. The preparation method of the ternary block copolymer polybenzimidazole high-temperature proton exchange membrane according to claim 13, characterized in that, The thickness of the copolymer solution forming a film on the flat plate is 1100 ± 200 microns, and the thickness after drying is 50 ± 10 microns.

16. A high-temperature proton exchange membrane fuel cell, characterized in that, Using the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane described in claim 11 or 12 as a battery separator, or the triblock copolymerized polybenzimidazole high-temperature proton exchange membrane prepared by the preparation method described in any one of claims 13 to 15 as a battery separator.

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