CN115020771B - HBM blending modified PBI proton exchange membrane and preparation method and application thereof - Google Patents

HBM blending modified PBI proton exchange membrane and preparation method and application thereof Download PDF

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CN115020771B
CN115020771B CN202210493112.XA CN202210493112A CN115020771B CN 115020771 B CN115020771 B CN 115020771B CN 202210493112 A CN202210493112 A CN 202210493112A CN 115020771 B CN115020771 B CN 115020771B
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pbi
hbm
proton exchange
exchange membrane
blending
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CN115020771A (en
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蔡卫卫
杨锋
李静
时佳维
周顺发
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China University of Geosciences
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China University of Geosciences
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
    • H01M8/1027—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having carbon, oxygen and other atoms, e.g. sulfonated polyethersulfones [S-PES]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
    • H01M8/103—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having nitrogen, e.g. sulfonated polybenzimidazoles [S-PBI], polybenzimidazoles with phosphoric acid, sulfonated polyamides [S-PA] or sulfonated polyphosphazenes [S-PPh]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
    • H01M8/1032—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having sulfur, e.g. sulfonated-polyethersulfones [S-PES]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
    • H01M8/1072—Polymeric electrolyte materials characterised by the manufacturing processes by chemical reactions, e.g. insitu polymerisation or insitu crosslinking
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

The invention discloses a proton exchange membrane based on HBM blending modification PBI, a preparation method and application thereof, and belongs to the field of fuel cells. The method comprises the following steps: mixing p-diaminobenzenesulfonic acid and trimesic acid in proportion, adding pyridine, N-methylpyrrolidone, triphenyl phosphite and anhydrous LiCl for polymerization reaction, and performing aftertreatment to obtain brown yellow HBM; and then blending the HBM and the PBI, and obtaining the modified PBI proton exchange membrane by a solution casting method. The hydrogen bond effect between molecules and in molecules of the HBM synthesized by the invention can establish an effective proton transmission channel, and the-NH 3 The blocked HBM molecules can better anchor phosphoric acid in PBI so that the phosphoric acid is not easy to run off, and a large amount of sulfonic acid groups are also introduced, so that the proton exchange efficiency is improved, and the proton conductivity of the PBI membrane is improved. The conductivity of the PBI proton exchange membrane modified by the blending method is improved at high temperature, and the attenuation of the proton conductivity of the modified PBI membrane is slowed down greatly after the modified PBI membrane is continuously tested at 180 ℃ for 100 hours.

Description

HBM blending modified PBI proton exchange membrane and preparation method and application thereof
Technical Field
The invention belongs to the technical field of fuel cells, and particularly relates to a proton exchange membrane material, in particular to a proton exchange membrane based on sulfonated hyperbranched macromolecules (HBM) blending modified Polybenzimidazole (PBI) and a preparation method and application thereof.
Background
The problems of environmental pollution and energy shortage are still the urgent need of the world today, and Proton Exchange Membrane Fuel Cells (PEMFC) are one of the most promising clean energy devices, which have high mass and volume specific power density, high energy conversion efficiency, almost zero emission in the case of using pure hydrogen as fuel, and environmental friendliness.
However, when the PEMFC works below 100 ℃, problems can occur, such as lower electrode reaction catalytic activity, catalyst poisoning caused by impurities in fuel, coexistence of gas and liquid phases in the battery, complex mass transfer regulation and control, complex water thermal management and higher cost. For these problems, selecting PEMFCs that operate at high temperatures (100 ℃ -200 ℃) is an effective solution. However, the proton conductivity of the traditional Nafion membrane is rapidly reduced under the high-temperature low-humidity environment, and the performance is seriously damaged, so that the key for developing the high-temperature proton exchange membrane fuel cell is to develop a high-temperature proton exchange membrane (HTPEM).
In order for PEMFCs to function properly under high temperature conditions, HTPEM materials need to meet the following conditions: high proton conductivity at high temperature, excellent mechanical property, good chemical stability, good thermal stability, long service life and the like. And Polybenzimidazole (PBI) is the most attention-paid high-temperature proton exchange membrane material at present due to the characteristics of high glass transition temperature, good thermal stability, high mechanical strength and the like. The electrochemical performance of PBI itself is extremely low and Phosphoric Acid (PA) doping is required to be used as a Proton Exchange Membrane (PEM), but PA-PBI has some problems that limit the application of PBI membranes. On the one hand, if the PA doping content is too low, the proton conductivity of the PBI film is poor; while the mechanical properties of the PBI membrane are severely degraded at higher PA levels. On the other hand, under the high-temperature (100-200 ℃) working condition, the phosphoric acid doped in the membrane is easy to run off, and the run-off phosphoric acid not only can reduce the proton conductivity of the proton exchange membrane, but also can poison the catalyst and corrode other parts of the cell, so that the performance and the service life of the fuel cell are seriously damaged.
Disclosure of Invention
In view of the above, the invention aims to provide a proton exchange membrane based on sulfonated hyperbranched macromolecule (HBM) blending modified Polybenzimidazole (PBI) and a preparation method and application thereof, so as to solve the defects of the PA doped PBI proton exchange membrane in the prior art.
In order to achieve the above object of the present invention:
in a first aspect, the invention provides a method for preparing a proton exchange membrane based on sulfonated hyperbranched macromolecules (HBM) blending modified Polybenzimidazole (PBI), comprising the following steps:
s1: mixing p-diaminobenzenesulfonic acid (DSA) and Trimesic Acid (TA) according to a certain proportion, adding a certain amount of pyridine, N-methylpyrrolidone, triphenyl phosphite and anhydrous LiCl, and carrying out polymerization reaction on the obtained mixed solution under the condition of inert atmosphere; washing and suction filtering after the reaction is finished, and then treating by NaOH solution and drying in vacuum to obtain brown yellow sulfonated hyperbranched macromolecules (HBM);
s2: and (2) blending the HBM prepared in the step (S1) with Polybenzimidazole (PBI) in an organic solvent, and obtaining the modified PBI proton exchange membrane based on the HBM blending modification by a solution casting method.
Further, the certain ratio in step S1 means that the molar ratio of DSA to TA is 2 or more and less than 3. For example, the molar ratio of DSA to TA may be 9: 4. 21:10...2:1, etc. In the invention, the molar ratio of DSA to TA is more than or equal to 3: 4. and less than 1: the carboxyl-terminated HBM formed at 1.
Optionally, the total mass of DSA and TA in step S1 is between 1 and 1.5g.
Alternatively, the amount described in step S1 is 3ml of pyridine, 4ml of N-methylpyrrolidone, 1ml of triphenyl phosphite, 0.4g of anhydrous LiCl.
Optionally, the polymerization reaction in step S1 is performed under the following reaction conditions: the reaction temperature is 100 ℃ and the reaction time is 0.5-2 h. The reaction time is determined according to the degree of polymerization, and the mixed solution generally becomes solid within 0.5 to 2 hours in a very short period of time, and the polymerization is completed. The different reaction times have no effect on the product.
Further, the inert atmosphere in step S1 is an argon atmosphere or a nitrogen atmosphere.
Optionally, in the step S1, the washing operation is performed with anhydrous methanol for three times and then with deionized water for three times.
Further, the concentration of the NaOH solution used in step S1 was 1mol/L, and the brown powder was sufficiently stirred in the NaOH solution for 12 hours.
Further, the temperature in the vacuum drying operation in step S1 was set to 100 ℃ and the drying time was 12 hours.
Further, in step S2, the organic solvent used for blending HBM and PBI is Dimethylsulfoxide (DMSO) or Dimethylformamide (DMF).
Optionally, the blending in step S2 is thoroughly stirred at 100 ℃ for 48 hours.
Optionally, in step S2, when blending with PBI, the mass fraction of HBM is 2.5-7.5%, more preferably 2.5-5% of the total mass of HBM and PBI.
Further, the blend of HBM and PBI was uniformly cast on a glass plate and dried on a hot plate at 80℃for 2 hours.
In a second aspect, the invention also provides a PBI proton exchange membrane based on HBM blending modification, which is prepared by adopting the method.
In a third aspect, the invention also provides application of the PBI proton exchange membrane based on HBM blending modification in fuel cells.
A fuel cell comprising the HBM blend modified PBI-based proton exchange membrane described above.
Compared with the prior art, the proton exchange membrane based on the HBM blending modification PBI and the preparation method and application thereof have the following beneficial effects:
in the present invention, an amino-terminated sulfonated hyperbranched polymer is synthesized by p-diaminobenzenesulfonic acid and trimesic acid in a specific ratio, and the polymer has excellent proton transfer efficiency due to a large number of sulfonic acid groups in the interior of the molecule. Because HBM is amino end-capped, the end capping group at the outermost layer of the molecule is-NH 3 Thus allowing more anchoring of the phosphate molecule. The HBM has good thermal stability and is excellent in heat stability,the working condition of the high-temperature fuel cell is completely met, the HBM is introduced into the PBI matrix, and good dispersibility and the creation of proton channels are realized by establishing a hydrogen bond network between the PBI and the HBM. The PBI proton exchange membrane obtained by blending modification is characterized by high-density sulfonate and a large amount of-NH 3 The proton transmission efficiency and proton conductivity of the PBI membrane are greatly improved by introducing the groups: the electrical conductivity of the PBI proton exchange membrane modified by the blending method is higher than that of an unmodified PBI membrane at a high temperature (110-180 ℃), and the attenuation of the proton electrical conductivity of the modified PBI membrane is also greatly slowed down after the modified PBI membrane is continuously tested at 180 ℃ for 100 hours. And due to the hyperbranched structure of HBM and-NH 3 The group anchors the PA molecule better, slowing down the phosphoric acid loss of the PBI membrane at high temperature.
Drawings
FIG. 1 is a synthetic scheme of the HBM synthesized in step S1 of example 1 of the present invention and the HBM of comparative example 1;
FIG. 2 is a process flow diagram of a sulfonated hyperbranched macromolecule blending modified PBI proton exchange membrane based on the invention;
FIG. 3 is a Nuclear Magnetic Resonance (NMR) spectrum of an amino-terminated HBM of example 1 and a carboxyl-terminated HBM of comparative example 1 of the present invention;
FIG. 4 is an infrared spectrum (FTIR) plot of an amino-terminated HBM in example 1 of the present invention versus a carboxyl-terminated HBM in comparative example 1;
FIG. 5 is an infrared spectrum (FTIR) plot of the modified PBI film versus the unmodified PBI film in examples 1-3 of the present invention;
FIG. 6 is an X-ray diffraction pattern (XRD) of the modified PBI film versus the unmodified PBI film of examples 1-3 of the present invention;
FIG. 7 is a Scanning Electron Microscope (SEM) image of the plane and cross section of the modified and unmodified PBI films of examples 1-3 of the present invention.
FIG. 8 is a 3D phase diagram of the modified PBI films of examples 1-3 of the present invention under an Atomic Force Microscope (AFM);
FIG. 9 is a graph of thermal weight loss of the modified PBI film versus the unmodified PBI film of examples 1-3 of the present invention;
FIG. 10 is a graph of the volume swell ratio test result and the PA doping ratio test result of the modified PBI film versus the unmodified PBI film in examples 1-3 of the present invention;
FIG. 11 is a graph of the conductivity of the modified and unmodified PBI films of examples 1-3 of the present invention at temperatures of 110℃to 180 ℃;
FIG. 12 is a proton conductivity diagram of the modified and unmodified PBI membranes of examples 1-3 of the present invention run at 180deg.C for a long period of time.
Detailed Description
The objects, technical solutions and advantages of the present invention will be more clearly and completely described in the following description in connection with the embodiments of the present invention.
For a better understanding of the present invention, and not to limit its scope, all numbers expressing quantities, percentages, and other values used in the present application are to be understood as being modified in all instances by the term "about". Accordingly, unless specifically indicated otherwise, the numerical parameters set forth in the specification are approximations that may vary depending upon the desired properties sought to be obtained. Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
The equipment and materials used in the present invention are commercially available or are commonly used in the art. The methods in the following examples are conventional in the art unless otherwise specified.
Example 1
As shown in FIG. 1, the preparation method of the PBI proton exchange membrane (PBI-HBM 5%) based on HBM blending modification comprises the following steps:
s1: mixing p-diaminobenzenesulfonic acid (DSA) and Trimesic Acid (TA) according to a certain proportion, adding a certain amount of pyridine, N-methylpyrrolidone, triphenyl phosphite and anhydrous LiCl, and carrying out polymerization reaction on the obtained mixed solution under the condition of inert atmosphere; washing and suction filtering after the reaction is finished, and then treating by NaOH solution and drying in vacuum to obtain brown yellow sulfonated hyperbranched macromolecules (HBM); wherein:
s2: and (2) blending the HBM prepared in the step (S1) with Polybenzimidazole (PBI) in an organic solvent, and obtaining the modified PBI proton exchange membrane based on the HBM blending modification by a solution casting method.
The structural formula of the p-Diaminobenzene Sulfonic Acid (DSA) is shown in the following formula I:
the structural formula of the Trimesic Acid (TA) is shown as the following formula II:
in the embodiment, the p-diaminobenzenesulfonic acid and trimesic acid are blended in a two-neck flask, then the two-neck flask is pumped with air three times and then inert atmosphere is introduced, 3ml of pyridine, 4ml of N-methylpyrrolidone and 1ml of triphenyl phosphite are added into the two-neck flask by a syringe, and the mixture is stirred for 0.5 to 2 hours at the temperature of 100 ℃. After the reaction is finished, the obtained solid is crushed, washed three times by absolute methanol and deionized water respectively, and filtered by suction, and then sulfonated hyperbranched macromolecules (HBM) are obtained. To allow better blending of the HBM with the PBI, the HBM was stirred in 1mol/l sodium hydroxide solution for 12h to neutralize the acidic groups in the HBM. The HBM was then dried in a vacuum oven at 100 ℃ for 12 hours to completely remove the residual solvent and water from the HBM, resulting in brown-yellow HBM particles.
In the examples herein, the amount of p-diaminobenzenesulfonic acid was 0.8g, trimesic acid was 0.447g, and the molar ratio DSA: ta=2: 1.
in the embodiment of the present application, the inert atmosphere used is an argon atmosphere.
In this example, 20mg of brown yellow granular HBM and 380mg of PBI powder were dissolved and blended in 5ml of dimethyl sulfoxide with stirring, the temperature was set at 100℃and the time was 48 hours. After the blending is finished, the mixed solution is cast on a glass plate, the film pushing device is adjusted to 60 mu m to push the solution flat, and the solution is placed on a heating plate, wherein the temperature is set to 80 ℃, and the drying time is set to 2 hours. Finally, the modified PBI proton exchange membrane with the thickness of about 40 mu m is obtained, wherein the mass fraction of HBM is 5%.
In the embodiment of the application, firstly, the sulfonated polymer is generated by the polymerization reaction of the p-Diaminobenzene Sulfonic Acid (DSA) and the Trimesic Acid (TA), and the outermost layer is formed by-NH in the hyperbranched molecular structure of the polymer because the DSA is excessive compared with the TA 3 The group is blocked, and sulfonate exists in DSA molecules, so that a large amount of sulfonate in HBM can greatly improve proton transmission efficiency. It is due to the large amount of sulfonate and-NH in HBM molecule 3 The group improves the proton conductivity of the membrane after being blended with PBI, and reduces the loss of phosphoric acid in the working state. Because of the excellent electrochemical performance of the HBM, the problems of insufficient PA doping and easy PA loss of the traditional PBI membrane are overcome after the HBM is blended with the modified PBI membrane, and finally the high proton conductivity and low PA loss rate of the modified PBI membrane at high temperature are realized, so that the modified PBI membrane has good application prospect.
Based on the same inventive concept, the embodiment of the application also provides a PBI proton exchange membrane based on HBM blending modification, which is prepared by adopting the preparation method.
Based on the same inventive concept, the embodiment of the application also provides the application of the PBI proton exchange membrane based on the HBM blending modification in fuel cells.
Comparative example 1
This comparative example is substantially identical to example 1, except that the molar ratio of DSA to TA in step S1 of this comparative example is 9:10 and that no sodium hydroxide solution is used after washing and suction filtration.
Example 2 (PBI-HBM 2.5%)
The difference from example 1 is that the mass of HBM added in this example is 2.5% of the total mass of HBM and PBI.
Example 3 (PBI-HBM 7.5%)
The difference from example 1 is that the mass of HBM added in this example is 7.5% of the total mass of HBM and PBI.
Characterization of the properties:
as shown in FIG. 1, the carboxylic acid on TAA radical (-COOH) and an amino radical (-NH) on DSA 2 ) An amide bond is formed by dehydration condensation. Theoretically, three DSA molecules and one TA molecule can form one macromolecule with three amino groups on the outermost layer centered on the TA molecule. Thus, when the molar ratio of DSA to TA is less than 3 and 2 or more, a polymer having all of the outermost amino groups is formed, and as the ratio is closer to 2:1, the polymerization degree of HBM obtained is higher (since the polymerization degree of the product is insufficient when the molar ratio of DSA to TA is 3:1, the solution cannot be polymerized into a solid state at the time of reaction, and therefore this ratio is not included). Similarly, when the DSA: TA molar ratio is greater than 3:4 is less than 1: carboxyl-terminated HBM is formed at 1. Since the amino-terminated HBMs of different degrees of polymerization are structurally similar and too much in proportion, only HBMs of one degree of polymerization (i.e., DSA to TA molar ratio of 2:1) are selected in the present invention and HBMs of other degrees of polymerization are not discussed.
Since carboxyl end-capped products are formed when trimesic acid is excessive during the synthesis of HBM, DSA: ta=2:1 in the present invention, the HBM formed is amino end-capped. As in fig. 3, two sets of characteristic absorption peaks at chemical shifts a of 11.8ppm and b of 10.9ppm are signals of hydrogen atoms of the end-capped carboxyl groups of the sulfonated hyperbranched macromolecular polymer, and the disappearance of these two signals in the amino-capped HBM can preliminarily confirm the successful synthesis of the amino-capped HBM. The characteristic absorption peak in the chemical shift a of 7 to 9ppm is lost, probably due to the treatment with sodium hydroxide solution at the time of the treatment of the amino-terminated HBM, and thus the signal of the hydrogen atom in the sulfonate group is lost.
As shown in FIG. 4, the infrared spectrum is 1745cm -1 And 1450cm -1 The characteristic peaks at this point are in turn the stretching vibration of the c=o group and the bending vibration of the O-H group of the carboxyl group in the carboxyl-terminated HBM. The characteristic peaks at both sites in the infrared spectrum of the amino-terminated HBM disappeared, further indicating the successful synthesis of the amino-terminated hyperbranched polyamide polymer. Since the signal and characteristic peak of the hydrogen atom of the end capping amino group of the sulfonated hyperbranched macromolecular polymer are not obvious, the polymer synthesized by the invention is proved to be the HBM of the end capping amino group by a reflection method in the figures 3 and 4.
FIG. 5 shows the preparation of examples 1 to 3, respectivelyInfrared spectrum (FTIR) image of the prepared modified PBI film and unmodified PBI film, the unmodified PBI film was obtained by solution casting with PBI powder. The infrared spectrum curve of the modified PBI film is 1200cm -1 And 1078cm -1 There are two new absorption peaks, which are symmetrical and asymmetrical vibrations from the sulfonic acid groups in the HBM. Fig. 6 is an XRD pattern of the modified and unmodified PBI films from which it can be seen that the PBI and its modified films have a broad peak at 2θ=24°, indicating the presence of amorphous and crystalline scattering, whereas the modified PBI film has a peak intensity decreasing with the addition of HBM, indicating that the amorphous regions in the modified PBI film increase with decreasing crystallinity, the increase in amorphous regions being beneficial for improving the conductivity of the proton exchange film. From FIGS. 5 and 6, it can be seen that the original structure of PBI is not destroyed after blending HBM with PBI.
Fig. 7 is an SEM image of the modified PBI membrane and the unmodified PBI membrane prepared in examples 1-3, in which it can be seen from a plan view that HBM is very uniformly mixed with PBI, and from a cross-sectional SEM image that the addition of HBM does not disrupt the dense structure of PBI.
Fig. 8 is an AFM phase diagram of three different HBM content modified PBIs with small differences in roughness, but as the mass fraction of HBM in PBI increases from 5% to 7.5%, HBM molecules become more susceptible to agglomeration, so that the phase separation of the modified PBI film becomes non-uniform, possibly due to stronger hydrogen bonding effect between HBM molecules. When the HBM content is low, the distribution of HBM molecules in the PBI film is more uniform; when the HBM content increases to some extent, agglomeration easily occurs between HBM molecules.
FIG. 9 is a thermal weight graph of a modified PBI film versus an unmodified PBI film with a ramp rate of 5 ℃/min. Through thermogravimetric tests we see that both the PBI film and the modified PBI film show good thermal stability, with three weight loss steps each. PBI films and composite films begin to lose weight at 100 ℃, due to residual water and solvent in the film. The modified PBI film begins a second stage of weight loss at 350 ℃ to 450 ℃ due to sulfonate degradation in the polymer. As the temperature increases, the backbone of the film begins to break, with the PBI film further losing weight around 550 ℃. The modified PBI membrane exhibits better thermal stability than the unmodified PBI membrane at temperatures between 150℃and 250℃which also results in a proton exchange membrane having better electrochemical properties at high temperatures.
Fig. 10 is the volume swell ratio of the modified PBI membrane and the unmodified PBI membrane immersed in Phosphoric Acid (PA) at 100 ℃ for 12 hours and the phosphoric acid doping ratio in PA at 100 ℃ for 72 hours. The volume swelling ratio was calculated as (V) 2 -V 1) /V 1 The PA doping ratio is calculated by (M 2 -M 1 )/M 1 Wherein V is 1 And V 2 The volumes of the films, 1X 3cm respectively, before and after 12h of immersion in Phosphoric Acid (PA) at 100 ℃. M is M 1 And M 2 The mass of the film was 1X 3cm before and after PA doping at 100℃for 72h, respectively. From comparison of the two sets of data, the modified PBI membrane had lower volume swell ratios at HBM mass fractions of 2.5% and 5%, respectively, by 50% and 46.2% as compared to the unmodified PBI membrane. The phosphate doping ratio of the modified PBI film is also improved compared to the unmodified PBI film. This demonstrates that the swelling resistance of the PBI film is enhanced by blending a proper amount of HBM to modify the PBI film, and that due to the large amount of-NH in the HBM 3 The group enables the composite membrane to adsorb more phosphoric acid molecules.
As shown in FIG. 11, when the doping amount of HBM is not more than 5%, the conductivity of the composite membrane is increased along with the increase of HBM content in the modified PBI membrane, and when the HBM content reaches 5%, the maximum conductivity of the composite membrane reaches 170mS/cm at 180 ℃, and compared with the unmodified PBI membrane, the proton conductivity of the modified PBI at 180 ℃ is improved by about 48%.
As can be seen in FIG. 11, the proton conductivity of the modified PBI film increases and decreases with increasing HBM content, and the conductivity decreases significantly when the HBM content increases from 5% to 7.5%, and the cause of the decrease in conductivity is also indicated by AFM or other characterization, so that the HBM content does not increase after increasing to 7.5% at most.
As shown in FIG. 12, proton conductivity test was performed on the modified PBI membrane and the unmodified PBI membrane under the condition of continuous operation at 180℃after the modified PBI membrane having HBM content of 5% was continuously heated at 180℃for 100 hoursConductivity was reduced by 26% and the conductivity of the PBI membrane was already reduced by 32% at 55 h. The modified PBI films of examples 1-3 all have some effect in alleviating PA loss compared to the unmodified PBI film because of the blocked-NH of the HBM 2 The PA molecule can be anchored better, and the PA molecule is not easy to run off due to the hydrogen bond effect in and among HBM molecules and the hyperbranched structure of the HBM.
The invention optimizes the properties of the PBI membrane in multiple aspects based on the method for modifying the PBI proton exchange membrane by blending the sulfonated hyperbranched macromolecules, and by adding a proper amount of HBM into the PBI membrane by the method for blending modification, the heat stability, swelling resistance, proton conductivity and the like of the PBI membrane are improved, and the PA loss condition of the PBI membrane at high temperature is relieved. The method is simple, has obvious effect and has good application prospect.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims (9)

1. A method for modifying PBI proton exchange membrane based on HBM blending is characterized in that: the method comprises the following steps:
s1: mixing the sulfanilic acid DSA and trimesic acid TA according to a certain proportion, adding a certain amount of pyridine, N-methylpyrrolidone, triphenyl phosphite and anhydrous LiCl, and carrying out polymerization reaction on the obtained mixed solution under the condition of inert atmosphere; washing, suction filtering, treating with NaOH solution, and vacuum drying to obtain brown sulfonated hyperbranched macromolecule HBM; the certain proportion refers to that the molar ratio of DSA to TA is more than or equal to 2 and less than 3;
s2: and (2) blending the HBM prepared in the step (S1) with polybenzimidazole PBI in an organic solvent, and obtaining the modified PBI proton exchange membrane based on the HBM blending modification PBI proton exchange membrane through a solution casting method.
2. The method according to claim 1, characterized in that: in the step S1, the total mass of DSA and TA is 1-1.5 g.
3. The method according to claim 1, characterized in that: the amount of pyridine in the step S1 was 3ml, N-methylpyrrolidone 4ml, triphenyl phosphite 1ml, and anhydrous LiCl 0.4g.
4. The method according to claim 1, characterized in that: the polymerization reaction in the step S1 is carried out under the following reaction conditions: the reaction temperature is 100 ℃ and the reaction time is 0.5-2 h.
5. The method according to claim 1, characterized in that: the blending in step S2 is carried out by stirring thoroughly at 100 ℃ for 48 hours.
6. The method according to claim 1, characterized in that: when the HBM and the PBI are blended, the mass fraction of the HBM and the PBI is 2.5-7.5%.
7. The proton exchange membrane based on HBM blending modification PBI prepared by the method of any one of claims 1 to 6.
8. The use of the HBM-based blend modified PBI proton exchange membrane prepared by the method of any one of claims 1 to 6 or the HBM-based blend modified PBI proton exchange membrane of claim 7 in a fuel cell.
9. A fuel cell, characterized in that: comprising the proton exchange membrane based on HBM blending modification PBI prepared by the method of any one of claims 1 to 6 or the proton exchange membrane based on HBM blending modification PBI of claim 7.
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