A high-oxidation-resistance polybenzimidazole proton exchange membrane, a preparation method and application thereof

Abstract

The application relates to the technical field of all-vanadium redox flow batteries, in particular to a high-oxidation-resistance polybenzimidazole proton exchange membrane as well as a preparation method and application thereof. The proton exchange membrane is prepared by mixing different high-oxidation-resistance polymer monomers in a reaction process to prepare polybenzimidazole block copolymers, and the membrane formed by the copolymers can realize rapid and selective proton conduction after being soaked in a high-concentration acid solution. In the application process of poly(2,2'-(p-oxydiphenyl)-5,5'-benzimidazole) in an all-vanadium redox flow battery, the polymer skeleton is easily oxidized by VO2 + , thereby causing the problems of battery capacity attenuation and continuous reduction of energy conversion efficiency, the application can effectively improve the microphase separation structure of the polybenzimidazole block copolymer membrane by synthesizing a high-oxidation-resistance polybenzimidazole block copolymer main chain, construct a rapid ion channel in the polybenzimidazole block copolymer membrane, and improve the utilization rate of an acid solution.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, specifically to a highly antioxidant polybenzimidazole proton exchange membrane, its preparation method, and its application. Background Technology

[0002] In the process of achieving decarbonization, the most effective measure is to minimize dependence on fossil fuels. To this end, it is essential to further develop renewable energy sources such as solar and wind power. However, the intermittency, seasonality, and volatility of wind and solar power generation lead to severe curtailment. Therefore, matching energy storage technologies are urgently needed. Flow batteries, due to their intrinsic safety, cycle life exceeding 20,000 cycles, and decoupling of power and capacity, have become the preferred direction for long-term energy storage. However, they currently face bottlenecks such as low power density, high initial investment (2.5 yuan / Wh), and reliance on imported core components such as ion-exchange membranes. Therefore, research on material innovation and structural optimization is urgently needed and is of great significance for overcoming energy storage technology bottlenecks and ensuring the achievement of "dual-carbon" goals.

[0003] Currently, vanadium redox flow batteries are the most mature flow battery technology due to their high energy conversion efficiency and high power density. However, the high initial investment and maintenance costs are the core bottleneck restricting their large-scale deployment. In terms of cost structure, the proton exchange membrane accounts for 30% of the total cost of a vanadium redox flow battery, and Nafion membranes are currently widely used. However, Nafion membranes have poor ion selectivity, and because they are manufactured by DuPont in the United States, their unit price is as high as $1000 / m³ due to the US's technological monopoly. 2 Therefore, researchers have conducted extensive research on non-fluorinated membrane materials, among which poly(2,2′-(p-oxybiphenyl)-5,5′-benzimidazole) (OPBI) is currently considered one of the most promising alternatives to Nafion membranes due to its unique vanadium-blocking properties and low manufacturing cost. However, the ether bonds on the OPBI polymer backbone are hydrophilic and have weak antioxidant properties, making it highly susceptible to VO2. + The attack ultimately affects battery efficiency, causing continuous capacity degradation.

[0004] During the polymerization process of OPBI polymer backbone, introducing polymer monomers with high antioxidant properties enhances the hydrophobicity of the OPBI polymer backbone, strengthens its antioxidant capacity, and improves the acid utilization rate of the membrane material. Therefore, designing and researching OPBI block polymer membrane materials with high ion selectivity, high ion conductivity, and high antioxidant properties will overcome the bottleneck problems of low energy conversion efficiency and significant capacity decay in all-vanadium redox flow batteries assembled from polybenzimidazole (PBI) membrane materials. Most importantly, significant cost reduction of all-vanadium redox flow batteries can be achieved through membrane material modification.

[0005] The patent with publication number CN119695217A proposes a high-temperature proton exchange membrane based on silicon-oxygen crosslinked polybenzimidazole and its preparation method. It uses a silane coupling agent to graft and form a silicon-oxygen network to improve the antioxidant properties. However, the crosslinked structure is prone to compressing the proton conduction channel, resulting in a decrease in proton conductivity. In addition, an additional acid-catalyzed crosslinking step is required, which increases the complexity of the process.

[0006] Patent CN106558719A discloses a high-temperature proton exchange membrane with high antioxidant properties, which is a cross-linked polybenzimidazole / polyvinylbenzyl chloride membrane and its preparation method. However, this method relies on spraying free radical quencher slurry on both sides of the membrane, which can easily lead to uneven membrane surface structure and affect the uniformity of proton conduction. The antioxidant layer only acts on the surface and does not improve the antioxidant properties from the polymer backbone. The coating is prone to peeling off during long-term use, and the antioxidant durability is limited. The introduction of the cross-linking agent polyvinylbenzyl chloride may increase the risk of membrane swelling.

[0007] The patent with publication number CN106356547A proposes a cross-linked polybenzimidazole / silica high-temperature proton exchange membrane with high antioxidant capacity and its preparation method. The porous inner layer is prepared by gas phase inversion method. The porous structure will reduce the mechanical strength of the membrane. The free radical quencher needs to be ultrasonically dispersed, which is prone to agglomeration and affects the uniformity of the antioxidant effect.

[0008] The patent with publication number CN104151587A proposes a novel method for preparing cross-linked polybenzimidazole proton exchange membranes. It uses halogenated compounds or epoxy compounds as cross-linking agents. Harmful substances may remain during the cross-linking process, affecting the electrolyte stability of vanadium redox flow batteries. It only enhances mechanical properties through cross-linking, without controlling the free volume and microporous structure of the polymer, and cannot balance proton conductivity and ion selectivity.

[0009] Therefore, it is of great significance to develop an OPBI matrix ion exchange membrane that simultaneously possesses antioxidant properties, high ion selectivity, low swelling, and high proton conductivity. Summary of the Invention

[0010] The purpose of this invention is to provide a high-oxidation-resistant polybenzimidazole proton exchange membrane, its preparation method, and its application, in order to solve the problems of capacity decay and low energy conversion efficiency caused by cross-permeation of vanadium ion electrolytes at the positive and negative electrodes of vanadium redox flow batteries and easy oxidation of OPBI membranes used in vanadium redox flow batteries.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A highly antioxidant polybenzimidazole proton exchange membrane, wherein the matrix component of the proton exchange membrane is a polymer, and the structure of the polymer backbone unit is shown in formula (I):

[0013]

[0014] The polymer backbone is a polybenzimidazole block copolymer, which is formed by block copolymerization of polybenzimidazole units and block units derived from monomer A. The molar percentage of polybenzimidazole units is m, the molar percentage of block units is n, m+n=100%, and 5%≤n≤50%. Monomer A is one or more of A1 to A4 mentioned above. A1 is 4,4'-isopropylidene dibenzoic acid, A2 is 2,2-bis(4-carboxyphenyl)hexafluoropropane, A3 is 4,4'-bis(carboxyphenoxy)diphenyl sulfone, and A4 is 4,4'-biphenyl dicarboxylic acid.

[0015] In the highly antioxidant polybenzimidazole proton exchange membrane, m refers to the molar percentage of polybenzimidazole units formed by the polymerization of 4,4'-diphenyl ether dicarboxylic acid and 3,3'-diaminobenzidine, and n refers to the molar percentage of block units formed by the polymerization of monomer A and 3,3'-diaminobenzidine.

[0016] The method for preparing the highly antioxidant polybenzimidazole proton exchange membrane includes the following steps:

[0017] S1. The polymer backbone is obtained by polymerizing monomer A, 4,4'-diphenyl ether dicarboxylic acid and 3,3'-diaminobenzidine under polyphosphoric acid catalysis. The mass ratio of monomer A, 4,4'-diphenyl ether dicarboxylic acid and 3,3'-diaminobenzidine to polyphosphoric acid is 1:1:2:100.

[0018] S2. Dissolve the polymer backbone obtained in step S1 in an organic solvent, stir evenly at 80-120°C, and cast and dry to form a film to obtain a polybenzimidazole block copolymer film. After soaking the polybenzimidazole block copolymer film in an acidic solution at 50-70°C for 24 hours, a polybenzimidazole proton exchange membrane with high antioxidant properties is obtained.

[0019] In the preparation method of the high antioxidant polybenzimidazole proton exchange membrane, in step S1, the polymerization temperature is 120℃~270℃ and the polymerization time is 2h~48h.

[0020] In the preparation method of the high antioxidant polybenzimidazole proton exchange membrane, in step S2, the organic solvent is one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide or N,N-dimethylformamide, and the mass ratio of the polymer backbone to the organic solvent is 1:10-50.

[0021] In the preparation method of the high antioxidant polybenzimidazole proton exchange membrane, in step S2, the acidic solution is one or more of acetic acid, phosphoric acid, trifluoroacetic acid, methanesulfonic acid, formic acid, pyruvic acid, and oxalic acid, and the mass ratio of the polybenzimidazole block copolymer membrane to the acidic solvent is 1:1000 to 10000.

[0022] The application of the highly antioxidant polybenzimidazole proton exchange membrane, which serves as the proton exchange membrane in an all-vanadium redox flow battery.

[0023] The application of the high-antioxidant polybenzimidazole proton exchange membrane in the vanadium redox flow battery involves a positive electrode electrolyte containing tetravalent and pentavalent vanadium ions, a negative electrode electrolyte containing divalent and trivalent vanadium ions, and a supporting electrolyte consisting of one or more of sulfuric acid, hydrochloric acid, or phosphoric acid. The molar ratio of the positive and negative electrode electrolytes is 1:1 to 2:1. The bipolar plate of the vanadium redox flow battery is a graphite bipolar plate, and the current collector is either carbon cloth or graphite carbon felt.

[0024] The design concept of this invention is:

[0025] This invention designs and prepares a highly antioxidant polybenzimidazole proton exchange membrane. This proton exchange membrane possesses a highly twisted rigid structure. By introducing a specific highly antioxidant monomer A, the free volume and micropore size of the polybenzimidazole polymer are controlled. This invention selects raw materials with high rigidity and high free volume to construct the polymer backbone (a polybenzimidazole block copolymer derivative). This constructs a fast ion channel in the polybenzimidazole block copolymer membrane while simultaneously improving the polymer's mechanical properties. The backbone structure design increases the free volume of the polybenzimidazole block copolymer membrane, constructing proton transport channels and reducing mass transfer resistance. Simultaneously, the increased free volume can accommodate water molecules, limiting the swelling of the membrane material, and the appropriate micropore size restricts the permeation of vanadium ions across the membrane. The strong hydrophilicity of the imidazole ring ensures that the highly antioxidant polybenzimidazole proton exchange membrane does not require additional hydrophilic treatment, making the membrane material preparation simple and under mild conditions.

[0026] This proton exchange membrane is prepared by mixing different polymeric monomers with high antioxidant properties during the reaction process to create a polybenzimidazole block copolymer. Membranes formed from this type of polymer can achieve rapid and selective proton transport without additional hydrophilic treatment after immersion in high-concentration acid. However, in the application of poly(2,2′-(p-oxybiphenyl)-5,5′-benzimidazole) in vanadium redox flow batteries, the polymer backbone is easily affected by VO2. +Ion oxidation leads to battery capacity decay and a continuous decrease in energy conversion efficiency. This invention addresses this problem by synthesizing a polybenzimidazole block copolymer backbone with high antioxidant properties, which can effectively improve the microphase separation structure of the polybenzimidazole block copolymer membrane, construct a fast ion channel within the polybenzimidazole block copolymer membrane, and improve the utilization rate of acid solution. In addition, this structure can effectively limit the swelling of the membrane material, thereby solving the above-mentioned technical pain points.

[0027] The advantages and beneficial effects of this invention are as follows:

[0028] This invention provides a method for preparing a polybenzimidazole proton exchange membrane with high antioxidant properties, thereby obtaining a proton exchange membrane suitable for vanadium redox flow batteries. This method improves the conductivity stability and antioxidant properties of the proton exchange membrane, enhances the cycle stability and energy efficiency of the vanadium redox flow battery, and reduces the production and preparation costs of the membrane material as well as the initial installation cost of the vanadium redox flow battery.

[0029] The proton exchange membrane contains a large number of antioxidant groups, such as -CF3, O=S=O, and -CH-. These groups lack lone pairs of electrons and exhibit good antioxidant properties. The -CF3 group blocks VO2 through steric hindrance. + Offensive, not easily affected by VO2 + Attacks can fundamentally enhance the antioxidant properties of OPBI polymers. The O=S=O groups stabilize the polymer backbone through electronic effects, while the -CH- groups indirectly improve the membrane's antioxidant stability by regulating the electron cloud distribution, flexibility, and steric hindrance of the polymer backbone. Simultaneously, the introduction of these groups increases the hydrophobicity of the polymer backbone, improves the microphase separation structure of OPBI polymers, reduces the acid doping level of OPBI, and increases the utilization rate of acid solutions, which is beneficial for improving the mechanical properties of OPBI membranes under actual operating conditions. Furthermore, high-oxidation-resistant polybenzimidazole proton exchange membranes have low raw material costs, are simple to synthesize, can be reused multiple times, and have low operating and maintenance costs, exhibiting a significant cost advantage.

[0030] Meanwhile, the vanadium redox flow battery is an aqueous battery with extremely high safety, and the prepared electrolyte can be recycled multiple times, making it environmentally friendly. Attached Figure Description

[0031] Figure 1 The graph shows the performance of the vanadium redox flow battery after 100 cycles in Example 2.

[0032] Figure 2 The graph shows the performance of the vanadium redox flow battery after 100 cycles, as shown in Comparative Example 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the embodiments of the present invention, all are configured as corresponding flow batteries. The test parameters and equipment are in accordance with the contents described in "NBT 42081-2016 Test Method for Single Cell Performance of Vanadium Redox Flow Battery". The test environment and steps are as follows:

[0035] Test environment:

[0036] Ambient temperature: 20℃±5℃;

[0037] —Air humidity: 50%±5%;

[0038] —Electrolyte temperature: 30℃±5℃.

[0039] Test steps:

[0040] a) Charge the battery system to 90% SOC;

[0041] b) The battery system operates at a current density of 200 mA / cm² 2 Discharge until the discharge cutoff voltage is reached;

[0042] c) The battery system operates at a current density of 200 mA / cm² 2 Continue charging until the charging cutoff voltage is reached;

[0043] d) The battery system operates at a current density of 200 mA / cm². 2 Discharge until the discharge cutoff voltage is reached;

[0044] e) Repeat steps c) through d);

[0045] f) Record the parameters for each charge-discharge cycle;

[0046] g) The average coulombic efficiency, voltage efficiency, and energy efficiency of the vanadium redox flow battery are the average values ​​of the data after multiple cycles.

[0047] The present invention will be further described in detail below through embodiments.

[0048] Example 1

[0049] In this embodiment, a method for preparing a proton exchange membrane for an all-vanadium redox flow battery is as follows:

[0050] 1. The matrix component of the selected proton exchange membrane is a polymer, and the structure of the polymer backbone unit is shown below:

[0051]

[0052] The polymer backbone is a polybenzimidazole block copolymer backbone, formed by block copolymerization of polybenzimidazole units and block units derived from monomer A. The molar percentage of polybenzimidazole units is m=51%, and the molar percentage of block units is n=49%. Among them, monomer A contains two carboxyl groups (-COOH) as copolymer active groups, and reacts with 3,3'-diaminobenzidine and 4,4'-diphenyl ether dicarboxylic acid. Monomer A is 4,4'-isopropylidene dibenzoic acid.

[0053] The preparation process of the proton exchange membrane is as follows:

[0054] S1. 4,4'-Isopropylidene dibenzoic acid, 4,4'-diphenyl ether dicarboxylic acid, and 3,3'-diaminobenzidine were dissolved in polyphosphoric acid and stirred at 160°C for 34 h to obtain a viscous polymer as the polymer backbone. The mass ratio of 4,4'-isopropylidene dibenzoic acid, 4,4'-diphenyl ether dicarboxylic acid, 3,3'-diaminobenzidine, and polyphosphoric acid was 1:1:2:100.

[0055] S2. The polymer backbone obtained in step S1 is dissolved in N,N-dimethylacetamide, stirred evenly at 100°C, and then cast and dried to form a film, yielding a polybenzimidazole block copolymer membrane. The polybenzimidazole block copolymer membrane is then immersed in methanesulfonic acid (80wt%) at 60°C for 24 hours to obtain a polybenzimidazole proton exchange membrane. The mass ratio of the polymer backbone to N,N-dimethylacetamide is 1:10, and the mass ratio of the polybenzimidazole block copolymer membrane to methanesulfonic acid is 1:2000.

[0056] In this embodiment, the thickness of the proton exchange membrane is 35 μm.

[0057] 2. The configuration of the all-vanadium redox flow battery is as follows:

[0058] Negative electrode: a solution of 1.6 mol / L divalent and trivalent vanadium ions, with the remainder being water;

[0059] Positive electrode: a solution of 1.6 mol / L tetravalent and pentavalent vanadium ions, with the remainder being water;

[0060] The flow battery is a single cell, with graphite electrodes as bipolar plates, graphite carbon felt as current collectors, and a highly antioxidant polybenzimidazole proton exchange membrane obtained in this embodiment. The flow battery's storage tank consists of two 0.1L capacity transparent bottles. A peristaltic pump serves as the power source between the storage tank and the battery stack. The negative electrode electrolyte volume is 0.1L, and the positive electrode electrolyte volume is 0.1L.

[0061] Example 2

[0062] The difference from Example 1 is that the matrix component of the proton exchange membrane used is a polymer, and the structure of the polymer backbone unit is shown below:

[0063]

[0064] The polymer backbone is a polybenzimidazole block copolymer backbone, formed by block copolymerization of polybenzimidazole units and block units derived from monomer A. The molar percentage of polybenzimidazole units is m=48%, and the molar percentage of block units is n=52%. Monomer A contains two carboxyl groups (-COOH) as copolymerization active sites and polymerizes with 3,3'-diaminobenzidine and 4,4'-diphenyl ether dicarboxylic acid. Monomer A is 2,2-bis(4-carboxyphenyl)hexafluoropropane.

[0065] The preparation process of the proton exchange membrane is as follows:

[0066] S1. Monomers A, consisting of 2,2-bis(4-carboxyphenyl)hexafluoropropane, 4,4'-diphenyl ether dicarboxylic acid, and 3,3'-diaminobenzidine, were dissolved in polyphosphoric acid and stirred at 200°C for 24 hours to obtain a viscous polymer as the polymer backbone. The mass ratio of 2,2-bis(4-carboxyphenyl)hexafluoropropane, 4,4'-diphenyl ether dicarboxylic acid, 3,3'-diaminobenzidine, and polyphosphoric acid was 1:1:2:100.

[0067] S2. The polymer backbone obtained in step S1 is dissolved in N,N-dimethylformamide, stirred evenly at 90°C, and then cast and dried to form a film, yielding a polybenzimidazole block copolymer membrane. The polybenzimidazole block copolymer membrane is then immersed in phosphoric acid (85 wt%) at 50°C for 24 hours to obtain a polybenzimidazole proton exchange membrane. The mass ratio of the polymer backbone to N,N-dimethylformamide is 1:40, and the mass ratio of the polybenzimidazole block copolymer membrane to phosphoric acid is 1:6000.

[0068] In this embodiment, the thickness of the proton exchange membrane is 35 μm.

[0069] The configuration of the positive and negative electrode electrolytes and the configuration of the flow battery are the same as in Example 1.

[0070] Example 3

[0071] The difference from Example 1 is that the matrix component of the proton exchange membrane used is a polymer, and the structure of the polymer backbone unit is shown below:

[0072]

[0073] The polymer backbone is a polybenzimidazole block copolymer backbone, formed by block copolymerization of polybenzimidazole units and block units derived from monomer A. The molar percentage of polybenzimidazole units is m=60%, and the molar percentage of block units is n=40%. Monomer A contains two carboxyl groups (-COOH) as copolymerization active sites and reacts with 3,3'-diaminobenzidine and 4,4'-diphenyl ether dicarboxylic acid. Monomer A is 4,4'-bis(carboxyphenoxy)diphenyl sulfone.

[0074] The preparation process of the proton exchange membrane is as follows:

[0075] S1. 4,4'-bis(carboxyphenoxy)diphenyl sulfone, 4,4'-diphenyl ether dicarboxylic acid, and 3,3'-diaminobenzidine were dissolved in polyphosphoric acid and stirred at 140°C for 48 h to obtain a viscous polymer as the polymer backbone. The mass ratio of 4,4'-bis(carboxyphenoxy)diphenyl sulfone, 4,4'-diphenyl ether dicarboxylic acid, 3,3'-diaminobenzidine, and polyphosphoric acid was 1:1:2:100.

[0076] S2. The polymer backbone obtained in step S1 is dissolved in N-methylpyrrolidone, stirred evenly at 120°C, and then cast and dried to form a film, yielding a polybenzimidazole block copolymer membrane. The polybenzimidazole block copolymer membrane is then immersed in pyruvate (6 wt%) at 70°C for 24 h to obtain a polybenzimidazole proton exchange membrane. The mass ratio of the polymer backbone to N-methylpyrrolidone is 1:20, and the mass ratio of the polybenzimidazole block copolymer membrane to pyruvate is 1:4000.

[0077] In this embodiment, the thickness of the proton exchange membrane is 35 μm.

[0078] The configuration of the positive and negative electrode electrolytes and the configuration of the flow battery are the same as in Example 1.

[0079] Example 4

[0080] The difference from Example 1 is that the matrix component of the proton exchange membrane used is a polymer, and the structure of the polymer backbone unit is shown below:

[0081]

[0082] The polymer backbone is a polybenzimidazole block copolymer backbone, formed by block copolymerization of polybenzimidazole units and block units derived from monomer A. The molar percentage of polybenzimidazole units is m=55%, and the molar percentage of block units is n=45%. Among them, the two carboxyl groups (-COOH) of monomer A serve as copolymerization active sites, and react with 3,3'-diaminobenzidine and 4,4'-diphenyl ether dicarboxylic acid in the polymerization reaction. Monomer A is 4,4'-biphenyl dicarboxylic acid.

[0083] The preparation process of the proton exchange membrane is as follows:

[0084] S1. 4,4'-biphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, and 3,3'-diaminobenzidine were dissolved in polyphosphoric acid and stirred at 260°C for 4 hours to obtain a viscous polymer as the polymer backbone. The mass ratio of 4,4'-biphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 3,3'-diaminobenzidine, and polyphosphoric acid was 1:1:2:100.

[0085] S2. The polymer backbone obtained in step S1 is dissolved in dimethyl sulfoxide, stirred evenly at 110°C, and then cast and dried to form a film, yielding a polybenzimidazole block copolymer membrane. The polybenzimidazole block copolymer membrane is then immersed in trifluoroacetic acid (99 wt%) at 60°C for 24 h to obtain a polybenzimidazole proton exchange membrane. The mass ratio of the polymer backbone to dimethyl sulfoxide is 1:50, and the mass ratio of the polybenzimidazole block copolymer membrane to trifluoroacetic acid is 1:8000.

[0086] In this embodiment, the thickness of the proton exchange membrane is 35 μm.

[0087] The configuration of the positive and negative electrode electrolytes and the configuration of the flow battery are the same as in Example 1.

[0088] Table 1. Flow Battery Test Table

[0089] <![CDATA[Antioxidant property mg L -1 > Coulomb efficiency % Voltage efficiency % Energy efficiency % Capacity retention rate % Example 1 0.09 99.11% 80.43% 79.72% 77.13% Example 2 0.085 99.15% 80.49% 79.81% 77.96% Example 3 0.079 99.42% 80.12% 79.66% 77.50% Example 4 0.087 99.33% 79.97% 79.44% 77.11%

[0090] like Figure 1 As shown, the vanadium redox flow battery of Example 2 underwent 100 charge-discharge cycle tests. The experiments demonstrate that the vanadium redox flow battery assembled from the highly antioxidant polybenzimidazole proton exchange membrane synthesized from 2,2-bis(4-carboxyphenyl)hexafluoropropane monomer exhibits good cycle stability and capacity retention. As shown in Table 1, the experimental results of Examples 1 to 4 are similar. Figure 1The coulombic efficiency was 99.11%–99.42%, the voltage efficiency was 79.97%–80.49%, the energy efficiency was 79.44%–79.81%, and the capacity retention was 77.11%–77.96%. Specific experimental data show that the high-oxidation-resistant polybenzimidazole proton exchange membrane battery constructed with reactant molecules possessing stronger hydrophobic functional groups exhibits better performance. In the oxidation resistance test using the pentavalent vanadium ion oxidation method, after immersion in Fenton's reagent at 25°C for 24 hours, the oxidation resistance (tetravalent vanadium ion concentration) in Examples 1 to 4 was 0.079 mg / L. -1 ~0.09mg L -1 In addition, the proton conductivity of Examples 1 to 4 is 33 mS / cm, 35 mS / cm, 32 mS / cm and 30 mS / cm respectively, which can be maintained in the range of 30 mS / cm to 35 mS / cm.

[0091] Comparative Example 1

[0092] The difference from Example 1 is that the comparative example is an all-vanadium redox flow battery, configured as follows:

[0093] Membrane material: OPBI;

[0094] Negative electrode: a solution of 1.6 mol / L divalent and trivalent vanadium ions, with the remainder being water, and a volume of 0.1 L.

[0095] Positive electrode: a solution of 1.6 mol / L tetravalent and pentavalent vanadium ions, with the remainder being water, and a volume of 0.1 L.

[0096] After assembly, perform battery cycle performance testing according to the test conditions described above. Figure 2 As shown, after 100 charge-discharge cycles, the battery showed a degradation rate of approximately 30%, a coulombic efficiency of 99.61%, an energy efficiency of 75.24%, and a voltage efficiency of 75.53%.

[0097] The experimental results above show that the high-oxidation-resistant polybenzimidazole proton exchange membrane provided by this invention greatly improves the stability and capacity retention of the vanadium redox flow battery.

[0098] Experimental results show that this invention designs and prepares a high-antioxidant-resistant polybenzimidazole proton exchange membrane (OPBI). By introducing reactant monomers with good antioxidant properties during the polymerization of polybenzimidazole polymer, the high-antioxidant-resistant OPBI polymer backbone is enhanced, while limiting membrane material swelling. By adjusting the number of hydrophobic functional groups, the microphase separation structure of the membrane material is improved, achieving rapid and selective proton conduction. While ensuring high ion selectivity, the conductivity of the high-antioxidant-resistant polybenzimidazole proton exchange membrane is improved, suppressing cross-contamination of positive and negative electrode active materials in vanadium redox flow batteries. This addresses the capacity decay and low energy efficiency issues of OPBI membranes in vanadium redox flow battery applications. Vanadium redox flow batteries using this series of proton exchange membranes maintain high energy efficiency and capacity retention after 100 charge-discharge cycles.

[0099] The above description of the present invention is merely to provide specific embodiments for those skilled in the art to facilitate understanding and execution. Various obvious modifications can be made to these embodiments by those skilled in the art, and the basic principles defined in the present invention can be applied in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention should not be limited to the embodiments shown in this document, and any other changes and modifications made to the present invention without departing from the spirit and scope of the invention should be covered by the claims of the present invention.

Claims

1. An application of a high-antioxidant polybenzimidazole proton exchange membrane, characterized in that, This proton exchange membrane serves as the proton exchange membrane for an all-vanadium redox flow battery. The matrix component of this proton exchange membrane is a polymer, and the structure of the polymer backbone unit is shown in formula (I): The polymer backbone is a polybenzimidazole block copolymer, formed by block copolymerization of polybenzimidazole units and block units derived from monomer A. The molar percentage of polybenzimidazole units is m, and the molar percentage of block units is n, where m+n=100% and 40%≤n≤49%. Monomer A is one or more of A1, A3, and A4 mentioned above. A1 is 4,4'-isopropylidene dibenzoic acid, A3 is 4,4'-bis(carboxyphenoxy)diphenyl sulfone, and A4 is 4,4'-biphenyl dicarboxylic acid. m refers to the molar percentage of polybenzimidazole units formed by the polymerization of 4,4'-diphenyl ether dicarboxylic acid and 3,3'-diaminobenzidine, and n refers to the molar percentage of block units formed by the polymerization of monomer A and 3,3'-diaminobenzidine. The method for preparing the highly antioxidant polybenzimidazole proton exchange membrane includes the following steps: S1. The polymer backbone is obtained by polymerizing monomer A, 4,4'-diphenyl ether dicarboxylic acid and 3,3'-diaminobenzidine under polyphosphoric acid catalysis. The mass ratio of monomer A, 4,4'-diphenyl ether dicarboxylic acid and 3,3'-diaminobenzidine to polyphosphoric acid is 1:1:2:

100. The polymerization temperature is 120℃~270℃ and the polymerization time is 2h~48h. S2. Dissolve the polymer backbone obtained in step S1 in an organic solvent, stir evenly at 80-120°C, and cast and dry to form a film to obtain a polybenzimidazole block copolymer film. After soaking the polybenzimidazole block copolymer film in an acidic solution at 50-70°C for 24 hours, a polybenzimidazole proton exchange membrane with high antioxidant properties is obtained.

2. The application of the high antioxidant polybenzimidazole proton exchange membrane according to claim 1, characterized in that, In step S2, the organic solvent is one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide or N,N-dimethylformamide, and the mass ratio of the polymer backbone to the organic solvent is 1:10 to 50.

3. The application of the high antioxidant polybenzimidazole proton exchange membrane according to claim 1, characterized in that, In step S2, the acidic solution is one or more of acetic acid, phosphoric acid, trifluoroacetic acid, methanesulfonic acid, formic acid, pyruvic acid, and oxalic acid, and the mass ratio of the polybenzimidazole block copolymer film to the acidic solution is 1:1000 to 10000.

4. The application of the high antioxidant polybenzimidazole proton exchange membrane according to claim 1, characterized in that, The positive electrode electrolyte of the vanadium redox flow battery is a solution containing tetravalent and pentavalent vanadium ions, and the negative electrode electrolyte is a solution containing divalent and trivalent vanadium ions. The supporting electrolyte is one or more of sulfuric acid, hydrochloric acid, or phosphoric acid. The molar concentration ratio of the positive electrode electrolyte to the negative electrode electrolyte is 1:1 to 2:

1. The bipolar plate of the vanadium redox flow battery is a graphite bipolar plate, and the current collector of the vanadium redox flow battery is one of carbon cloth and graphite carbon felt.

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