Sulfonated polybenzothiazole-based composite proton exchange membrane using sulfonated oxidized graphene as inorganic filler and method for preparing the same

Abstract

The application relates to the field of proton exchange membrane preparation, and provides a sulfonated polybenzothiazole composite proton exchange membrane taking sulfonated graphene oxide as inorganic filler and a preparation method thereof. A composite proton exchange membrane with functional inorganic filler is prepared by introducing sulfonated graphene oxide into a polymer sulfonated polybenzothiazole matrix. The application has the beneficial effects that: the preparation process of the proposed proton exchange membrane is mild and easy to control, raw materials are cheap and easy to obtain; the synthesized polymer matrix has good solubility, so that the prepared composite proton exchange membrane is complete without any damage; the existence of acidic groups in the sulfonated graphene oxide produces strong interfacial interaction between the graphite surface and the polymer matrix, thereby improving the thermal stability and mechanical stability of the membrane; in addition, the acidic groups can provide more auxiliary jumping sites for proton movement in the membrane, thereby enhancing the proton conductivity of the membrane.

Description

Technical Field

[0001] This invention relates to proton exchange membranes and their preparation methods, particularly to sulfonated polybenzothiazole-based composite proton exchange membranes using sulfonated graphene oxide as an inorganic filler and their preparation methods. Background Technology

[0002] In recent years, proton exchange membrane fuel cells (PEMFCs) have become the preferred power source for transportation, stationary, and portable electricity applications due to their advantages such as high efficiency, high power density, continuous power generation, environmental friendliness, and rapid start-up. The proton exchange membrane (PEM) is the core component of a PEMFC. During operation, it not only acts as an electrolyte providing a pathway for hydrogen ions but also serves as a separator between the reactant gases at the electrodes. Therefore, the performance of the PEM significantly impacts the performance, cost, and application of the PEMFC. The basic properties of a PEMFC include good mechanical and thermal properties, high proton conductivity, considerable durability, compatibility with other fuel cell components, and low production costs. Over the past few decades, perfluorosulfonic acid polymer membranes (Nafion) have been the most commercially valuable PEMFC due to their excellent mechanical stability and high proton conductivity at standard PEMFC operating temperatures (<80°C). However, despite its superior performance, Nafion membranes no longer meet the demands of PEMFC development and changing operating conditions. Using Nafion membranes, which operate only at low temperatures (<100°C), can lead to defects in proton exchange membrane fuel cell systems, such as low impurity tolerance and slow kinetic processes. Sulfonated polybenzothiazole proton exchange membranes are a type of high-temperature proton exchange membrane developed in recent years, possessing high mechanical properties, high oxidation resistance, and excellent chemical stability. However, their water absorption and swelling rate increase with increasing temperature, which in turn affects the membrane's proton conductivity and mechanical properties, reducing its lifespan.

[0003] To address the above issues, a method for preparing sulfonated polybenzothiazole-based composite proton exchange membranes using sulfonated graphene oxide as an inorganic filler is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a sulfonated polybenzothiazole-based composite proton exchange membrane using sulfonated graphene oxide as an inorganic filler and its preparation method. Firstly, sulfonated polybenzothiazole with the following repeating unit structure is synthesized as a matrix via direct polycondensation.

[0005]

[0006] The structure of X1 is generated by the corresponding sulfonated aromatic dicarboxylic acid. Depending on the selected sulfonated aromatic dicarboxylic acid monomer, the sPBT structure contains one or more X1 structures. The following formula lists different X1 structures and their corresponding sulfonated aromatic dicarboxylic acid monomers. In this invention, sPBT with a sulfonated biphenyl group is used as an example, that is, the selected sulfonated aromatic dicarboxylic acid monomer is 3,3'-disulfonylbiphenyl-4,4'-dicarboxylic acid.

[0007]

[0008] The X2 structure is generated by the corresponding aromatic dicarboxylic acid. Depending on the selected aromatic dicarboxylic acid monomer, the sPBT structure contains one or more X2 structures. The following formula lists different X2 structures and their corresponding aromatic dicarboxylic acid monomers. In this invention, sPBT containing ether bond units is used as an example, that is, the selected aromatic dicarboxylic acid monomer is 4,4-dicarboxylic diphenyl ether.

[0009]

[0010] Secondly, functionalized flake graphite was used as a filler and incorporated into the sPBT matrix by solution casting to prepare a film.

[0011] The present invention provides a method for preparing a proton exchange membrane, comprising the following preparation steps:

[0012] (1) Preparation of graphene oxide (GO): Flake graphite was subjected to ice bath, KMnO4 oxidation, dilution, acid washing and magnetic stirring under acidic conditions to obtain a suspension. The suspension was centrifuged, washed with water until neutral, and finally freeze-dried to obtain GO.

[0013] (2) Preparation of sulfonated graphene oxide (SGO): The GO obtained in (1) was dissolved in water, and after sonication and centrifugation, a GO solution was obtained. The solution was sulfonated with 3-mercaptopropyltrimethoxysilane (MPTMS) and NaH. The solid product was then filtered and soaked in HCl aqueous solution, rinsed with ethanol, and finally dried under vacuum to obtain SGO.

[0014] (3) Preparation of sulfonated polybenzothiazole (sPBT) as polymer matrix: 2,5-diamino-1,4-benzenedithiophenol dihydrochloride (DABDT), 2,4-dicarboxylic acid diphenyl ether (PE) and sodium 3,3'-disulfonate-4,4'-dicarboxylic acid biphenyl (SCBP) were polymerized by direct polycondensation, followed by filtration, salt leaching, water washing, and finally vacuum drying to obtain sPBT.

[0015] (4) Preparation of composite proton exchange membrane (SGO-sPBT): The sPBT obtained in (3) is heated and dissolved to obtain a polymer solution, the SGO obtained in (2) is added and sonicated, and the SGO-sPBT membrane is obtained by solution casting and heating and drying.

[0016] Preferably, in step (1), the acid used is 98% sulfuric acid and the mass fraction of sodium nitrate is 50%; the oxidation reaction temperature is 50℃ and the reaction time is 5h; the acid used for pickling is a 10% HCl aqueous solution.

[0017] Preferably, in step (1), the centrifugation speed is 7000 rpm and the centrifugation time is 10 min; the freeze-drying temperature is -40℃ and the time is 24 h.

[0018] Preferably, in step (2), the concentration of GO solution is 0.8 mg / mL; the power value of ultrasonic treatment is 1000 W, and ultrasonic treatment is performed for 30 min at 90% energy output value; the centrifugation speed is 7000 rpm, and the centrifugation time is 10 min.

[0019] Preferably, in step (2), the amount of 3-mercaptopropyltrimethoxysilane used is 12.28 mmol, the reaction temperature is 80℃, and the reaction time is 24 h; the mass of NaH used is 1.5 g, the reaction temperature is 60℃, and the reaction time is 6 h.

[0020] Preferably, in step (2), the volume ratio of HCl to H2O in the HCl aqueous solution is 1:1, the soaking time is 12h, the number of ethanol rinsings is 5, the vacuum drying temperature is 80℃, and the drying time is 24h.

[0021] Preferably, in step (3), the molar concentration of SCBP is 57.5%; the solution used for salt leaching is a 5wt% Na2CO3 solution, and the leaching time is 48h; the vacuum drying temperature is 100℃, and the drying time is 24h.

[0022] Preferably, in step (4), the solution is DMSO, the concentration of sPBT solution is 0.02 g / mL; the power value of ultrasonic treatment is 1000 W, and ultrasonic treatment is performed for 15 min at 90% energy output value; the temperature of solution casting is 70℃ and the time is 36 h.

[0023] Preferably, in step (4), the mass percentages of SGO are 0, 1 wt%, 2 wt%, 3 wt%, and 4 wt%.

[0024] The method for preparing the proton exchange membrane provided by this invention has the following advantages compared with the prior art:

[0025] (1) The preparation process of the proton exchange membrane proposed in this invention uses inexpensive and readily available raw materials, and the reaction process is mild and easy to control.

[0026] (2) The polymer matrix prepared by the present invention has good solubility, which makes the prepared proton exchange membrane intact and without any damage.

[0027] (3) This invention provides a strategy for producing composite proton exchange membranes with inorganic nanofiller SGO. The presence of acidic groups in SGO generates strong interfacial interactions between the graphite surface and the polymer matrix, thereby improving the thermal and mechanical stability of the membrane. In addition, the acidic groups in SGO can also provide more auxiliary hopping sites for proton movement within the membrane, enhancing the proton conductivity of the membrane. Attached Figure Description

[0028] Figure 1 The sulfonated polybenzothiazole (sPBT) prepared in Example 1 1 H NMR spectrum;

[0029] Figure 2 SEM images of the composite proton exchange membrane prepared in Example 2. (a, b, c, d, and e represent (0 wt%) SGO-sPBT, (1 wt%) SGO-sPBT, (2 wt%) SGO-sPBT, (3 wt%) SGO-sPBT, and (4 wt%) SGO-sPBT, respectively.) Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described 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.

[0031] Example 1:

[0032] 1) Preparation of graphene oxide (GO): 2g of flake graphite and 2g of NaNO3 were added to a 500mL beaker. Then, 90mL of H2SO4 was added under ice bath conditions, and the mixture was magnetically stirred for 30min. Subsequently, 10g of KMnO4 was added to the beaker in four portions, each 10min apart. The ice bath was then removed, and the reaction was carried out under 50℃ oil bath heating with magnetic stirring for 5h. The beaker was then removed from the oil bath, and 200mL of deionized water was added while stirring with a glass rod, followed by 12mL of H2O2, and finally 50mL of HCl solution. Stirring continued until homogeneous, and the mixture was transferred to centrifuge tubes. After centrifugation, the solid product was placed in a petri dish and frozen for 24h, followed by freeze-drying for 24h. Graphene oxide (GO) was thus obtained.

[0033] 2) Preparation of sulfonated graphene oxide (SGO): GO (0.2 g) was dispersed in deionized water (250 mL) and sonicated until the solution became homogeneous. Unexfoliated graphene oxide was removed by centrifuging the GO solution at 7000 rpm for 10 min to remove undispersed GO. Then, NaH (1.5 g) was slowly added to the GO deionized water solution (250 mL), and the mixture was stirred in an oil bath at 60 °C for 6 h. Next, MPTMS (28 mmol) was added dropwise to the reaction mixture, and the mixture was stirred again in an oil bath at 80 °C for 24 h. The reaction mixture was filtered and soaked in an HCl / deionized water solution (1:1) for 12 h, then washed five times with ethanol to remove residues. Finally, the product was vacuum dried at 80 °C for 24 h. Sulfonated graphene oxide (SGO) was obtained.

[0034] 3) Preparation of the polymer matrix sulfonated polybenzothiazole (sPBT): In a three-necked round-bottom flask (100 mL) equipped with a nitrogen inlet / outlet and a mechanical stirrer, DABBT (0.45 g, 1.8352 mmol) was dissolved in PPA (12.4 g). The mixture was stirred at room temperature for 12 h, and then heated in an oil bath at 70 °C with continuous stirring for 24 h until HCl stopped precipitating. After cooling to room temperature, SCBP (0.4711 g, 1.0552 mmol) and PE (0.2014 g, 0.7800 mmol) were added, and the mixture was stirred at 100 °C for 8 h. Subsequently, additional P2O5 (3.8 g) was added, and the mixture was heated as follows: 120 °C for 3 h, 150 °C for 3 h, 170 °C for 3 h, 190 °C for 12 h, and 210 °C for 12 h. After the reaction, the viscous mixture was cooled to 140°C and then poured into deionized water to obtain a reddish-brown fibrous polymer. The product was washed several times with deionized water to remove residual acid, and then soaked in a 5 wt% Na₂CO₃ solution for 48 h. Finally, the product was washed until a neutral pH was reached and dried under vacuum at 100°C for 24 h. This yielded the polymer matrix sulfonated polybenzothiazole (sPBT). See [link to product details]. Figure 1 via SPBT 1 The 1H NMR spectrum shows that the polymer exhibits sharp and clear signal peaks, and each signal peak can be well assigned to the individual H atoms of sPBT. Notably, due to the different chemical environments of the polybenzothiazole, the H4 and H4′ signal peaks show different shapes, indicating that the presence of the sulfonation group causes H atoms to split. 1 The 1H NMR spectrum provides excellent evidence for the chemical structure of sPBT.

[0035] Example 2:

[0036] 1) Preparation of the composite proton exchange membrane ((0wt%) SGO-sPBT): 0.2 g of sPBT was dissolved in 10 mL of DMSO and heated to 120 °C until completely dissolved. Impurities in the solution were then filtered out to obtain a homogeneous polymer solution, which was cast onto a clean glass plate and dried at 70 °C for 36 h. After cooling to room temperature, the glass plate was immersed in deionized water, and the salt membrane was then peeled off. Subsequently, it was converted into an acidic membrane by soaking in 1 M HCl for 48 hours. The acidic membrane was washed repeatedly with deionized water to remove residual acid. The composite proton exchange membrane ((0wt%) SGO-sPBT) was thus obtained.

[0037] 2) Preparation of the composite proton exchange membrane ((1wt%) SGO-sPBT): 0.198 g of sPBT was dissolved in 10 mL of DMSO and heated to 120 °C until completely dissolved. Impurities in the solution were then filtered out to obtain a homogeneous polymer solution. 0.002 g of SGO was then dispersed into the sPBT solution using a water bath ultrasonic method to obtain a uniformly dispersed mixed solution. The solution was then cast onto a clean glass plate and dried at 70 °C for 36 h. After cooling to room temperature, the glass plate was immersed in deionized water, and the salt membrane was then peeled off. Subsequently, the membrane was converted to an acidic membrane by soaking in 1 M HCl for 48 hours. The acidic membrane was repeatedly washed with deionized water to remove residual acid. The composite proton exchange membrane ((1wt%) SGO-sPBT) was thus obtained.

[0038] 3) Preparation of the composite proton exchange membrane ((2wt%) SGO-sPBT): 0.196 g of sPBT was dissolved in 10 mL of DMSO and heated to 120 °C until completely dissolved. Impurities in the solution were then filtered out to obtain a homogeneous polymer solution. 0.004 g of SGO was then dispersed into the sPBT solution using a water bath ultrasonic method to obtain a uniformly dispersed mixed solution. The solution was then cast onto a clean glass plate and dried at 70 °C for 36 h. After cooling to room temperature, the glass plate was immersed in deionized water, and the salt membrane was then peeled off. Subsequently, the membrane was converted to an acidic membrane by soaking in 1 M HCl for 48 hours. The acidic membrane was repeatedly washed with deionized water to remove residual acid. The composite proton exchange membrane ((2wt%) SGO-sPBT) was thus obtained.

[0039] This invention also prepared (3wt%) SGO-sPBT and (4wt%) SGO-sPBT at mass percentages of 3wt% and 4wt%, respectively; the specific steps are not described here. The difference between (3wt%) SGO-sPBT and (4wt%) SGO-sPBT lies in the mass percentage of SGO in the polymer solution; in (3wt%) SGO-sPBT, the mass percentage of SGO is 3wt%, and in (4wt%) SGO-sPBT, the mass percentage of SGO is 4wt%. Figure 2 As can be seen, the surface of the composite proton exchange membrane (0wt%) SGO-sPBT is smooth, and no particle morphology was observed; the particle state of (1wt%) SGO-sPBT is more obvious, showing an aggregated state; the surface particles of (2wt%) SGO-sPBT are partially dispersed, and particle clustering occurs; the surface particles of (3wt%) and (4wt%) SGO-sPBT are uniformly dispersed and clearly visible. This indicates that SGO can be well dispersed in the sPBT matrix, and the composite proton exchange membrane SGO-sPBT was successfully prepared.

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

Claims

1. A method for preparing a sulfonated polybenzothiazole-based composite proton exchange membrane using sulfonated graphene oxide as an inorganic filler, characterized in that, The preparation steps include the following: (1) Preparation of graphene oxide: Flake graphite was subjected to ice bath, KMnO4 oxidation, dilution, acid washing and magnetic stirring under acidic conditions to obtain a suspension. The suspension was centrifuged, washed with water until neutral, and finally freeze-dried to obtain graphene oxide. (2) Preparation of sulfonated graphene oxide: The graphene oxide obtained in (1) was dissolved in water, and after sonication and centrifugation, a graphene oxide solution was obtained. It was then sulfonated with 3-mercaptopropyltrimethoxysilane and NaH, and then filtered to obtain a solid product. The product was soaked in HCl aqueous solution, rinsed with ethanol, and finally vacuum dried to obtain sulfonated graphene oxide. (3) Preparation of sulfonated polybenzothiazole as polymer matrix: 2,5-diamino-1,4-benzenedithiophenol dihydrochloride, 2,4-dicarboxylic acid diphenyl ether and 3,3'-disulfonate sodium-4,4'-dicarboxylic acid biphenyl were polymerized by direct polycondensation, followed by filtration, salt leaching, water washing, and finally vacuum drying to obtain sulfonated polybenzothiazole as polymer matrix. (4) Preparation of composite proton exchange membrane: The sulfonated polybenzothiazole obtained in (3) is heated and dissolved to obtain a polymer solution. The sulfonated graphene oxide obtained in (2) is added and sonicated. The solution is cast and dried to obtain the sulfonated graphene oxide-polymer matrix sulfonated polybenzothiazole membrane. The sulfonated graphene oxide accounts for 3 wt% or 4 wt% of the sum of the polymer matrix sulfonated polybenzothiazole and the sulfonated graphene oxide.

2. The preparation method according to claim 1, characterized in that: In step (1), the acid used was 98% sulfuric acid; the oxidation reaction temperature was 50℃ and the reaction time was 5h; the acid used for pickling was 10% HCl aqueous solution; the centrifugation speed was 7000rpm and the centrifugation time was 10min; the freeze-drying temperature was -40℃ and the time was 24h; in step (2), the ultrasonic treatment power was 1000W, and the ultrasonic treatment was performed at 90% energy output for 30min; the centrifugation speed was 7000rpm and the centrifugation time was 10min; the amount of 3-mercaptopropyltrimethoxysilane used was 12.28mmol, the reaction temperature was 80℃ and the reaction time was 24h; the mass of NaH used was 1.5g, the reaction temperature was 60℃ and the reaction time was 6h; the volume ratio of HCl to H2O in the HCl aqueous solution was 1:1 and the soaking time was 12h; the number of ethanol rinses was 5; the vacuum drying temperature was 80℃ and the drying time was 24h.

3. The preparation method according to claim 1, characterized in that: In step (3), the molar concentration of sodium 3,3'-disulfonate-4,4'-dicarboxybiphenyl is 57.5%; the salt leaching solution is a 5wt% Na2CO3 solution, and the leaching time is 48h; the vacuum drying temperature is 100℃, and the drying time is 24h.

4. The preparation method according to claim 1, characterized in that: In step (4), DMSO was used as the solution and the concentration of the polymer solution was 0.02 g / mL. The ultrasonic power was 1000 W and the ultrasonic treatment was performed for 15 min at 90% energy output. The solution casting method was carried out at a temperature of 70 °C for 36 h.

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