CN113563619B - Preparation method of branched-crosslinked sulfonated polyimide membrane - Google Patents
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Abstract
The invention discloses a preparation method of branched-crosslinked sulfonated polyimide film, which comprises the steps of obtaining a novel branched-crosslinked polyimide film material by a casting film forming method and a high-temperature polymerization method through a Y-type branched triamine monomer, an X-type crosslinked tetramine monomer, a sulfonated diamine monomer, a non-sulfonated diamine monomer and an anhydride monomer. The Y-type branching monomer and the X-type crosslinking tetramine monomer are synthesized by themselves. The molar ratio of the cross-linked tetramine, the non-sulfonated diamine, the anhydride, the branched triamine, the sulfonated diamine and the benzoic acid is as follows: the crosslinking degree of the diaphragm can be controlled by regulating and controlling the proportion of the dosage of the crosslinking monomer in the invention to be 0.06-0.14:0.07-0.23:1:0.1:0.5:2. The stability and vanadium resistance of the membrane can be effectively improved by introducing the branched crosslinking structure, and the problems of efficiency, service life and the like of the all-vanadium redox flow battery can be effectively improved. In conclusion, the branched-crosslinked sulfonated polyimide membrane prepared by the method has good application prospect in the field of all-vanadium redox flow batteries.
Description
Technical Field
The invention belongs to the field of battery diaphragms, and relates to a preparation method of a branched-crosslinked sulfonated polyimide membrane.
Background
With the continuous development of economy, the problem of renewable energy utilization is more and more emphasized, so that the energy storage and conversion system needs to play a vital role in energy application. all-Vanadium Redox Flow Battery (VRFB) is an excellent energy storage system and has the advantages of high response speed, long service life, good reliability, strong deep discharge capacity and the like. Proton Exchange Membranes (PEM) are one of the important component materials of VRFB to separate the positive and negative electrolytes to avoid cross-contamination of vanadium ions and conduct protons to loop the cell. Thus, the PEM should have high proton conductivity, excellent vanadium resistance, and outstanding chemical stability. Heretofore, nafion membranes produced by dupont in the united states have been widely used in VRFB systems because of their high proton conductivity and excellent chemical stability. However, nafion membranes are severely vanadium permeable, have low proton selectivity and are expensive to sell, thus limiting their large-scale commercial application in VRFB.
To date, sulfonated aromatic polymer membranes are of increasing interest to researchers, for example: sulfonated poly (arylethersulfone) (SPPES), sulfonated poly (etheretherketone) (SPEEK), sulfonated poly (phenylene) oxide (SPPO), sulfonated Polybenzimidazole (SPBI), and Sulfonated Polyimide (SPI) membranes. Among these films, SPI films exhibit excellent application potential in VRFB applications due to various advantages of excellent film forming property, low vanadium ion permeability, low cost, high proton selectivity, and the like. However, the study of SPI film in VRFB is still preliminary, and its shortcomings are mainly in the following two aspects: (1) In the strong acid strong oxidizing electrolyte environment, the SPI film has weak chemical stability, and seriously affects the service life of the SPI film in a battery; (2) The unobvious hydrophilic-hydrophobic phase separation structure enables the proton conductivity of the SPI membrane to be low, and is not beneficial to the battery to obtain higher voltage efficiency. Therefore, there is a need to greatly improve the chemical stability and proton conductivity of SPI membranes, so that they can be commercially applied in VRFB. To overcome the above problems, many researchers have studied that the prior art (Long J, xu WJ, xu SB, liu J, wang YL, luo H, et al Anovel double branched sulfonated polyimide membrane with ultra-high proton selectivity for vanadium redox flow battery, J membrane Sci 628 (2021) 119259) has successfully prepared a double branched sulfonated polyimide (dbSPI) membrane having higher proton conductivity and lower vanadium permeability than a linear sulfonated polyimide (l-SPI) membrane. In addition, when a branched structure is introduced into the SPI, the performance of the VRFB can be greatly improved, but the chemical stability of the SPI film material prepared by the prior art is not excellent enough.
The invention aims to overcome the defects and short plates of the SPI film, prepare a branched-crosslinked SPI film with good chemical stability and proton conduction level, and correspondingly provide a preparation method and main application fields thereof.
In the present invention, the "X" type 4,4',4", 4'" (5, 5 '-benzimidazole-2, 2') -tetraaniline (BTA) and "Y" type 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene (TFAPOB) were synthesized and introduced into SPI film, so that both crosslinked and branched structures were obtained. In addition, the C-F bond contained in the Y-type monomer is very stable, so that the attack probability of V (V) can be reduced, and the chemical stability of the SPI film is effectively improved. The branched structure may provide a greater free volume for the membrane, thereby improving its proton conducting capacity. The introduction of the cross-linked structure can also strengthen the chemical and dimensional stability of the SPI membrane.
Disclosure of Invention
It is an object of the present invention to address at least the above problems and/or disadvantages and to provide at least the advantages described below.
To achieve these objects and other advantages and in accordance with the purpose of the invention, there is provided a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 1,4,5, 8-naphthalene tetracarboxylic anhydride (NTDA), benzoic acid and m-cresol I into a reactor, and stirring and dissolving at room temperature; adding 2,2' -disulfonic acid Benzidine (BDSA), triethylamine and m-cresol II into a container, stirring at 50-70 ℃ until the materials are dissolved, sequentially adding 4,4' (5, 5' -benzimidazole-2, 2 ') -tetraaniline (BTA), 4' -diaminodiphenyl ether (ODA) and 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene (TFAPOB) into the container, stirring at 50-70 ℃ until the materials are dissolved, then placing the materials in the container into a constant pressure dropping funnel, dripping the materials into the reactor, and stirring at 30-100 ℃ for 4-8 hours after the dripping is completed to obtain casting film liquid; pouring the casting solution on a dry and clean glass plate, casting the casting solution into a film, then drying the glass plate at 60-80 ℃ for 10-24 h, and then drying the glass plate at different temperatures of 80-150 ℃ for 0.5-3 h to obtain a triethylamine type branched-crosslinked sulfonated polyimide film;
step two, placing the triethylamine branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol, soaking for 18-48 h, and then placing in 1.0-3.0 mol L -1 Soaking in sulfuric acid water solution for 24-48 h, washing with deionized water for 5-10 times to obtain branched-crosslinked sulfonated polyimide film, soaking in deionized water and preserving.
Preferably, the molar ratio of 4,4',4", 4'" (5, 5 '-benzimidazole-2, 2') -tetraniline, 4 '-diaminodiphenyl ether, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene, 2' -disulfonic acid benzidine and benzoic acid is: 0.06-0.14:0.07-0.23:1:0.1:0.5:2.
Preferably, the volume ratio of the m-cresol I to the m-cresol II is 1:1; the volume ratio of the total volume of the m-cresol I and the m-cresol II to the triethylamine is as follows: 20-70:0.5-9.5; the dosage ratio of the triethylamine to the 2,2' -disulfonic acid benzidine is as follows: every time 0.4-3.2 mmol of 2,2' -disulfonic acid benzidine is added, the volume of the added triethylamine is 0.5-9.5 mL.
Preferably, the m-cresol I and the m-cresol II can be replaced by one or more than two of N, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.
Preferably, the thickness range of the casting film is controlled as follows: 25-120 mu m.
Preferably, the absolute ethyl alcohol can be replaced by one or a mixture of more than two of methyl alcohol, acetone and isopropyl alcohol; the deionized water may be replaced with distilled water or ultrapure water.
Preferably, in the first step, after the dripping is completed, stirring and reacting for 1-2 hours at the temperature of 30-100 ℃ to obtain a casting solution, placing the casting solution into a microwave and ultrasonic integrated reactor, and simultaneously starting microwaves and ultrasonic waves for cooperative treatment for 30-45 min, wherein the microwave power is 150-350W; the ultrasonic power is 300-800W, the ultrasonic frequency is 45-65 KHz, and the reaction temperature is 30-100 ℃.
Preferably, in the first step, pouring the film casting solution after the cooperative treatment on a dry and clean glass plate for casting film, and then carrying out electron beam irradiation with the irradiation dose of 4-10 Gy; drying the glass plate in an infrared drying oven for 6-8 hours, wherein the power is 800-1000W and the temperature is 50-60 ℃; and then drying for 0.5-3 hours at different temperatures of 80-150 ℃ respectively to obtain the triethylamine type branched-crosslinked sulfonated polyimide film.
The invention at least comprises the following beneficial effects:
compared with the existing technology of the sulfonated polyimide film prepared by VRFB, the invention has the following characteristics and advantages: the invention aims to overcome the defects of weaker chemical stability and insufficient proton conductivity of a sulfonated polyimide film for VRFB, and takes fluorine-containing Y-type branched triamine monomer, X-type cross-linked tetramine monomer, non-sulfonated diamine monomer, dianhydride monomer and sulfonated diamine monomer with mass transfer capability as raw materials to prepare the sulfonated polyimide film containing branching-cross-linking; the prepared branched-crosslinked sulfonated polyimide film can obviously improve the interaction between molecular chains and the space free volume, thereby enhancing the vanadium resistance, the proton conductivity and the application potential in the VRFB field. Furthermore, the "X" type self-crosslinking tetraamine monomer can be modified by: 4,4',4", 4'" (5, 5 '-benzimidazole-2, 2') -tetraaniline and non-sulfonated diamine monomer: the proportion of 4,4' -diaminodiphenyl ether can effectively regulate and control the crosslinking degree of the diaphragm, thereby solving the problems of weaker chemical stability and lower proton conductivity of the sulfonated polyimide film in a targeted manner. The invention prepares fluorine-containing 'Y' -shaped branched triamine monomer needed by branched-crosslinked sulfonated polyimide film: 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene and "X" type self-crosslinking tetraamine monomer: the synthesis of 4,4' (5, 5' -benzimidazole-2, 2 ') -tetraaniline is shown in FIGS. 2 and 3, respectively.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Description of the drawings:
FIG. 1 is a reaction scheme for preparing a branched-crosslinked sulfonated polyimide membrane of the present invention;
FIG. 2 is a synthetic scheme of 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene (TFAPOB) of the present invention;
FIG. 3 is a synthetic scheme of 4,4' (5, 5' -benzimidazole-2, 2 ') -tetraaniline (BTA) according to the present invention;
FIG. 4 is a FTIR spectrum of 4,4' (5, 5' -benzimidazole-2, 2 ') -tetraniline (BTA) according to the present invention;
FIG. 5 shows 4,4' (5, 5' -benzimidazole-2, 2 ') -tetraaniline (BTA) according to the present invention 1 H NMR spectrum;
FIG. 6 is a FTIR spectrum of a sc-bSPI film of the present invention;
FIG. 7 shows a sc-bSPI-14 film of the present invention 1 H NMR spectrum;
FIG. 8 shows VO through sc-bSPI film of the present invention 2+ Ion concentration profile;
FIG. 9 is an open circuit voltage curve for a sc-bSPI-14 film of the present invention;
FIG. 10 is a coulombic efficiency curve of a sc-bSPI-14 film of the present invention;
FIG. 11 is a voltage efficiency curve of a sc-bSPI-14 film of the present invention;
FIG. 12 is an energy efficiency curve of a sc-bSPI-14 film of the present invention;
FIG. 13 is a cycle test curve for sc-bSPI-14 films of the present invention.
The specific embodiment is as follows:
the present invention is described in further detail below with reference to the drawings to enable those skilled in the art to practice the invention by referring to the description.
It will be understood that terms, such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
Example 1:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.92mmol ODA and 0.24mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 60 ℃ for 15 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; pouring the casting solution on a dry and clean glass plate, casting to form a film, and drying at 60 ℃ for 15h; drying at 80 ℃,100 ℃,120 ℃ and 150 ℃ for 1h respectively to obtain the branched-crosslinked sulfonated polyimide film of triethylamine salt;
step two, placing the obtained triethylamine type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol for soaking for 24 hours to remove residual solvent and monomer which does not participate in reaction; then, soaking in 1.0mol L -1 The solution is put into sulfuric acid for 24 hours to complete the protonation process; finally, washing with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-6);
the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 51. Mu.m; ion Exchange Capacity (IEC) of 1.65mmol g -1 dry。
Example 2:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.76mmol ODA and 0.32mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 60 ℃ for reacting for 12 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; pouring the casting solution on a dry and clean glass plate, casting to form a film, and drying at 60 ℃ for 15h; drying at 80 ℃,100 ℃,120 ℃ and 150 ℃ for 1h respectively to obtain the branched-crosslinked sulfonated polyimide film of triethylamine salt;
step two, placing the obtained triethylamine type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol for soaking for 24 hours to remove residual solvent and monomer which does not participate in reaction; then, soaking in 1.0mol L -1 The solution is put into sulfuric acid for 24 hours to complete the protonation process; finally, washing with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-8);
the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 50 μm; ion Exchange Capacity (IEC) of 1.60mmol g -1 dry。
Example 3:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.6mmol ODA and 0.4mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 60 ℃ for reaction for 10 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; pouring the casting solution on a dry and clean glass plate, casting to form a film, and drying at 60 ℃ for 15h; drying at 80 ℃,100 ℃,120 ℃ and 150 ℃ for 1h respectively to obtain the branched-crosslinked sulfonated polyimide film of triethylamine salt;
step two, soaking the obtained triethylamine-type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L -1 The mixture is placed in sulfuric acid solution for 24 hours to complete the protonation process, and finally the mixture is washed with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-10);
the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 51. Mu.m; ion Exchange Capacity (IEC) of 1.51mmol g -1 dry。
Example 4:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.44mmol ODA and 0.48mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 60 ℃ for reaction for 8 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; pouring the casting solution on a dry and clean glass plate, casting to form a film, and drying at 60 ℃ for 15h; drying at 80 ℃,100 ℃,120 ℃ and 150 ℃ for 1h respectively to obtain the branched-crosslinked sulfonated polyimide film of triethylamine salt;
step two, putting the obtained triethylamine salt type branched-crosslinked sulfonated polyimide film into absolute ethyl alcohol to be soaked for 24 hoursTo remove the residual solvent and the monomer which does not participate in the reaction, and then soaking in 1.0mol L -1 The mixture is placed in sulfuric acid solution for 24 hours to complete the protonation process, and finally the mixture is washed with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-12);
the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 51. Mu.m; ion Exchange Capacity (IEC) of 1.42mmol g -1 dry。
Example 5:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.28mmol ODA and 0.56mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 40 ℃ for 6 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; pouring the casting solution on a dry and clean glass plate, casting to form a film, and drying at 60 ℃ for 15h; drying at 80 ℃,100 ℃,120 ℃ and 150 ℃ for 1h respectively to obtain the branched-crosslinked sulfonated polyimide film of triethylamine salt;
step two, soaking the obtained triethylamine-type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L -1 The mixture is placed in sulfuric acid solution for 24 hours to complete the protonation process, and finally washed with deionized water for 7 times to obtain a branched-crosslinked sulfonated polyimide film (sc-bSPI-14);
the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 50 μm; ion Exchange Capacity (IEC) of 1.36mmol g -1 dry; wherein the commercial Nafion 212 membrane has a thickness of 51 μm; ion Exchange Capacity (IEC) of 0.92mmol g -1 dry; has higher ion exchange capacity and is beneficial to proton transfer.
Example 6:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.28mmol ODA and 0.56mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 40 ℃ for 2 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; placing the casting solution in a microwave and ultrasonic integrated reactor, and simultaneously starting microwave and ultrasonic to carry out cooperative treatment for 45min, wherein the microwave power is 350W; the ultrasonic power is 800W, the ultrasonic frequency is 45KHz, and the reaction temperature is 50 ℃; pouring the treated casting solution on a dry and clean glass plate, casting to form a film, and drying at 60 ℃ for 15h; drying at 80 ℃,100 ℃,120 ℃ and 150 ℃ for 1h respectively to obtain the branched-crosslinked sulfonated polyimide film of triethylamine salt;
step two, soaking the obtained triethylamine-type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L -1 The mixture is placed in sulfuric acid solution for 24 hours to complete the protonation process, and finally deionized water is used for washing 7 times to obtain the branched-crosslinked sulfonated polyimide film; the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 50 μm;
the branched-crosslinked sulfonated polyimide membrane prepared in this example was tested in an all vanadium redox flow battery (test method consistent with sc-bSPI-14 membrane maintenance), and was used at 200mA cm -2 The coulombic efficiency CE at high current density of 99.42%, the voltage efficiency VE 66.31% and the energy efficiency EE 66.82%; sc-bSPI-14 film at 200mA cm -2 Is 99.22%, 64.14% for voltage efficiency VE and 64.44% for energy efficiency EE; branching prepared in this example0.1mol L of crosslinked sulfonated polyimide film immersed in 40 DEG C -1 VO 2 + +3.0mol L -1 H 2 SO 4 The solution was left for 15 days and VO was recorded every 3 days with a spectrophotometer 2+ During 15 days of soaking, the branched-crosslinked sulfonated polyimide film produced 0.39mol L due to strong acid and strong oxidizing environment -1 g -1 VO of (2) 2+ The method comprises the steps of carrying out a first treatment on the surface of the While sc-bSPI-14 film was 0.41mol L -1 g -1 VO of (2) 2+ 。
Example 7:
a method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 8.0mmol of benzoic acid, 20mL of m-cresol I and 4.0mmol of NTDA into a 250mL three-necked flask, and stirring at 60 ℃ until the solid is completely dissolved; then, 2.0mmol BDSA, 20mL m-cresol II and 2.6mL triethylamine are placed in a beaker, after stirring at 60 ℃ until the solid is completely dissolved, 0.4mmol TFAPOB, 0.28mmol ODA and 0.56mmol BTA are added, after the solid is completely dissolved, the solution is slowly dripped into the three-necked flask by utilizing a constant pressure funnel, and after stirring at 40 ℃ for 2 hours, the branched-crosslinked sulfonated polyimide casting film liquid is obtained; placing the casting solution in a microwave and ultrasonic integrated reactor, and simultaneously starting microwave and ultrasonic to carry out cooperative treatment for 45min, wherein the microwave power is 350W; the ultrasonic power is 800W, the ultrasonic frequency is 45KHz, and the reaction temperature is 50 ℃; pouring the film casting solution after the synergistic treatment on a dry and clean glass plate for casting film, and then carrying out electron beam irradiation with the irradiation dose of 8Gy; drying the glass plate in an infrared drying oven for 6 hours, wherein the power is 1000W and the temperature is 60 ℃; drying at 80 deg.c, 100 deg.c, 120 deg.c and 150 deg.c for 1 hr to obtain triethylamine type branched-crosslinked sulfonated polyimide film;
step two, soaking the obtained triethylamine-type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol for 24 hours to remove residual solvent and unreacted monomers, and then soaking in 1.0mol L -1 The mixture is placed in sulfuric acid solution for 24 hours to complete the protonation process, and finally the mixture is washed with deionized water for 7 times to obtain branched-crosslinked sulfonated polyimideA membrane; the branched-crosslinked sulfonated polyimide film prepared in this example had a thickness of 50 μm;
the branched-crosslinked sulfonated polyimide membrane prepared in this example was tested in an all vanadium redox flow battery (test method consistent with sc-bSPI-14 membrane maintenance) and was 200mAcm -2 The coulombic efficiency CE at high current density of 99.78%, the voltage efficiency VE 67.45% and the energy efficiency EE 67.78%; sc-bSPI-14 film at 200mA cm -2 The coulombic efficiency CE at high current density of 99.22%, the voltage efficiency VE of 64.14% and the energy efficiency EE of 64.44%. The branched-crosslinked sulfonated polyimide film prepared in this example was immersed in 0.1mol L at 40 ℃ -1 VO 2 + +3.0mol L -1 H 2 SO 4 The solution was left for 15 days and VO was recorded every 3 days with a spectrophotometer 2+ During 15 days of soaking, the branched-crosslinked sulfonated polyimide film produced 0.37mol L due to strong acid and strong oxidizing environment -1 g -1 VO of (2) 2+ The method comprises the steps of carrying out a first treatment on the surface of the While sc-bSPI-14 film was 0.41mol L -1 g -1 VO of (2) 2+ 。
The FTIR spectrum of BTA in the present invention is shown in FIG. 4, BTA is 3203cm -1 And 3315cm -1 The peak at this point is attributed to-NH 2 Is stretched out and stretched into 1780cm -1 There is no absorption peak, which means that-COOH in DBA has been consumed, 1446cm -1 The peak at this point was attributable to symmetrical vibration of the imidazole ring, demonstrating successful BTA monomer synthesis.
BTA is also analyzed 1 The structure was further confirmed by H NMR spectroscopy, and the results are shown in fig. 5. The peak in FIG. 5 is at 4.95ppm (H 1 )、5.97ppm(H 2 )、6.64ppm(H 3 )、7.49ppm(H 4 )、7.66ppm(H 5 )、7.84ppm(H 6 )、12.58ppm(H 7 ). Actual peak area ratio (H 1 :H 2 :H 3 :H 4 :H 5 :H 6 :H 7 =2.09:0.48:1.05:0.52:0.56:0.45:0.46) very close to the theoretical value (H 1 :H 2 :H 3 :H 4 :H 5 :H 6 :H 7 The exact synthesis of BTA was verified by =4:1:2:1:1:1:1).
The chemical structures of the branched-crosslinked sulfonated polyimide films prepared in examples 1 to 5 were characterized by FTIR spectra, and the results are shown in fig. 6. Characteristic peak 1710cm -1 And 1667cm -1 Can belong to asymmetric and symmetric stretching vibration of carbonyl. 1450cm -1 The peak at this point is due to the symmetrical vibration of the imidazole ring on the BTA monomer, and the asymmetrical vibration of C-N on the imide ring is at 1351cm -1 。1249cm -1 Is attributed to vibration of-O-. Furthermore, 1135cm -1 The characteristic absorption peak at this location is attributed to-CF on TFAPOB monomer 3 Vibration of the group. -SO 3 Characteristic absorption peaks for H groups appear at 1196, 1098 and 1028cm -1 . Furthermore, at 1780cm -1 No significant polyimide acid absorption peak appears nearby, indicating that the branched-crosslinked sulfonated polyimide film is fully imidized. Thus, FTIR spectra indicated that branched-crosslinked sulfonated polyimide films have been successfully prepared from NTDA, BDSA, TFAPOB, ODA and BTA monomers.
sc-bSPI-14 film 1 The H NMR spectrum is shown in FIG. 7. Chemical shifts at 8.79ppm (He) and 8.61ppm (Hf) correspond to protons of the NTDA naphthalene ring. Peaks at 8.24ppm (Hg) and 7.77ppm (Hh) belong to the benzene hydrogen of ODA. Chemical shifts at 8.14ppm, 7.95ppm and 7.79ppm are due to Hi, hk and Hj on BDSA. Chemical shifts of 6.59ppm (Hd), 7.58ppm (Ha), 7.60ppm (Hb) and 7.64ppm (Hc) are ascribed to the phenylhydrogen of TFAPOB. 6.54 The signals at (Hm), 6.57 (Hl), 7.74 (Hn), 8.02 (Hp), 8.24 (Hq) are H-shifts on the BTA. These characteristic peaks also confirm successful synthesis of sc-bSPI-14 membranes.
The branched-crosslinked sulfonated polyimide membranes prepared in the examples were each subjected to the following performance test, as follows:
(1) Vanadium ion permeability test:
the prepared branched-crosslinked sulfonated polyimide membrane is clamped between two diffusion cells, and 1.0mol L of the membrane is respectively filled at the left side and the right side of the membrane -1 VO 2+ +2.0mol L -1 H 2 SO 4 Solution and 1.0mol L -1 MgSO 4 +2.0mol L -1 H 2 SO 4 A solution; every otherTaking out the sample solution from the right side cell of the membrane for a fixed time, and measuring VO by using an ultraviolet-visible spectrophotometer 2+ The absorbance of the ion to calculate VO passing through the membrane at that time by using a standard curve 2+ Ion concentration (as shown in fig. 8); pouring the sample solution back into the right side pool after each test; the vanadium ion permeability of the diaphragm is calculated as follows:
wherein V is the volume of solution (cm) on the left and right sides of the membrane 3 )；C t VO in solution on right side of film at time t (min) 2+ Concentration of ions (mol L) -1 )；C L Is VO in solution at the left side of the membrane 2+ Initial concentration of ions (mol L) -1 ) The method comprises the steps of carrying out a first treatment on the surface of the A is the effective area (cm) of the diaphragm 2 ) The method comprises the steps of carrying out a first treatment on the surface of the P is VO of the diaphragm 2+ Ion permeability (cm) 2 min -1 ) The method comprises the steps of carrying out a first treatment on the surface of the The branched-crosslinked sulfonated polyimide membranes of each example were tested 3 times under the same conditions, and the results were averaged;
the vanadium ion permeabilities of the branched-crosslinked sulfonated polyimide membranes of examples 1 to 7 are shown in Table 1.
(2) Proton conductivity test:
the conductivity cell was divided into two compartments using a soaked membrane, both of which were filled with solution. Finally, under the conditions that constant current is 5.0mA and frequency is 1.0 Hz-100 kHz, impedance (R) of the conducting cell when the membrane is arranged is measured by using CHI660E type electrochemical workstation manufactured by Shanghai Chen Hua instruments Co., ltd 1 ). The impedance (R) of the conductivity cell without the membrane was measured using the same test method using the same conductivity cell, the distance between the electrodes, and the volume of the electrolyte in the two compartments were kept consistent 0 ). The proton conductivity of the membrane is calculated as follows:
wherein σ is the proton conductivity of the membrane (S cm -1 )，R 0 And R is 1 Impedance of the conductivity cell without and with membrane, respectively, A is the effective area (cm) of the membrane 2 ) D is the thickness (cm) of the separator;
the proton conductivities of the branched-crosslinked sulfonated polyimide membranes of examples 1 to 7 are shown in table 1.
(3) Proton selectivity:
the Proton Selectivity (PS) of the membrane is defined as the ratio of proton conductivity to vanadium ion permeability, which can be used to evaluate the overall performance of the membrane as follows:
proton selectivities of the branched-crosslinked sulfonated polyimide membranes of examples 1 to 7 are shown in table 1:
TABLE 1
As can be seen from Table 1 and FIG. 8, the branched-crosslinked sulfonated polyimide films of examples 1 to 5 have a vanadium ion permeability (1.0 to 2.31X10 -7 cm 2 min -1 ) Are all lower than Nafion 212 (7.48×10) -7 cm 2 min -1 ) The prepared branched-crosslinked sulfonated polyimide film has excellent vanadium resistance. The reason is attributable to the strong Donna repellent effect of the imidazole group on vanadium ions in the BTA monomer. And secondly, the membrane is crosslinked, so that intermolecular interaction is enhanced, a denser structure is formed, and the migration of vanadium is effectively resisted. To sum up, the following description is provided: the cross-linked membrane can effectively prevent vanadium ion cross-penetration.
Sigma of the branched-crosslinked sulfonated polyimide membranes and Nafion 212 membranes of examples 1-5 are shown in Table 1. sigma of sc-bSPI-14 membrane is very close to Nafion 212 membrane.
Finally, the branched-crosslinked sulfonated polyimide film should have a higher sigma and lower P, so that a high PS can be obtained, thereby promoting VRFB performanceLifting. sc-bSPI-14 membrane has the highest PS among all membranes (2.78X10 5 S min cm -3 ) And is a Nafion 212 membrane (0.43X10) 5 S min cm -3 ) About 6 times as large as the above.
To further identify the vanadium resistance of sc-bSPI-14 and Nafion 212 films, the self-discharge behavior of VRFB using sc-bSPI-14 and Nafion 212 films was investigated, and the results are shown in FIG. 9. The OCV of sc-bdpi-14 and Nafion 212 membranes showed similar trend of change, with the open circuit voltage slowly decreasing before 1.3V and then rapidly decreasing to 0.8V. The self-discharge life (defined as the time before the OCV remains above 0.8V) of the sc-bSPI-14 film was 46h. The OCV of sc-bSPI-14 is approximately four times that of Nafion 212 (11 h). The results show that: sc-bSPI-14, which has a branched and crosslinked structure, has a stronger vanadium blocking capability than Nafion 212.
Because the sc-bSPI-14 membrane showed the highest proton selectivity among all membranes, the sc-bSPI-14 membrane was selected for testing cell performance (the prepared membrane was applied to an all vanadium redox flow battery for testing, and compared with an all vanadium redox flow battery using a commercial Nafion 212 membrane). The sc-bSPI-14 membrane prepared in the embodiment 5 of the invention and the commercial Nafion 212 membrane are used for assembling an all-vanadium redox flow battery, and the battery performance of the membrane is verified. 1.7mol L of the liquid is put into the positive and negative liquid storage tanks -1 VO 3.5+ +4.7mol L -1 50mL of sulfuric acid solution, and the electrolyte was fed into the battery by a magnetic pump. And a Xinwei battery detection system (CT-4008T-5V/12A-204 n-F) is used for carrying out constant current charge and discharge test (current density is 200-80 mA cm) -2 ) The voltage range is 0.8-1.65V. The coulomb efficiency, energy efficiency and voltage efficiency can be calculated using the formula:
coulombic efficiency = discharge capacity/charge capacity x 100%
Energy efficiency = discharge energy/charge energy x 100%
Voltage efficiency = energy efficiency/coulombic efficiency x 100%
The coulombic, voltage, and energy efficiency, VE, EE, results are shown in fig. 10-11. sc-bSPI-14 (99.2-97.1%) has a CE higher than Nafion 212 (94.5-86.5%).Such results indicate that sc-bSPI-14 has a lower permeability to vanadium ions. When the current density is from 80mA cm -2 Rising to 200mA cm -2 At this time, the CE of both sc-bSPI-14 and Nafion 212 membranes became higher at high current densities. At 80 to 200mA cm -2 In the lower case, the VE of the Nafion 212 membrane is higher than the sc-bSPI-14 membrane because Nafion 212 has a higher proton conductivity. This is because the Nafion 212 membrane contains a hydrophobic polytetrafluoroethylene backbone and hydrophilic alkyl perfluorosulfonate side chains, which structure can greatly improve its proton conductivity. Thus, sc-bSPI-14 membrane VE is lower than Nafion 212. As the current density increases, VE decreases for both sc-bSPI-14 and Nafion 212 membranes. However, the Nafion 212 membrane showed a faster VE decline rate than the sc-bSPI-14 membrane, indicating a better balance between σ and P for the sc-bSPI-14 membrane. Furthermore, EE is the most important indicator for measuring VRFB energy conversion and storage capacity. sc-bSPI-14 film at 200 to 80mA cm -2 Shows higher EE values (64.6-82.8%) than Nafion 212 membranes (60.5-78.5%), which results are identical to proton selectivity results. The results show that: the sc-bSPI-14 film has excellent VRFB application prospect.
To evaluate the stability of the sc-bSPI-14 film in VRFB, the sc-bSPI-14 film was tested at 140mA cm -2 1000 cycles of testing were performed as shown in fig. 13. sc-bSPI-14 exhibited good battery stability (CE. Apprxeq.98.4%, VE. Apprxeq.76.8% and EE. Apprxeq.75.6%) in 1000 cycle testing of VRFB, demonstrating its excellent cycle stability.
To investigate the chemical stability of the membrane, sc-bSPI-14 membrane was immersed in 0.1mol L at 40 ℃ -1 VO 2 + +3.0mol L -1 H 2 SO 4 The solution was left for 15 days and VO was recorded every 3 days with a spectrophotometer 2+ Is a concentration of (3). During the 15 day soak, the sc-bSPI-14 membrane produced 0.41mol L due to the strong acid and strong oxidizing environment -1 g -1 VO of (2) 2+ And compared with the dbSPI50 membrane of the prior art (Long J, xu WJ, xu SB, liu J, wang YL, luo H, et al A novel double branched sulfonated polyimide membrane with ultra-high proton selectivity for vanadium redox flow battery, J Member Sci 628 (2021) 119259), dbSPI50The film produced 0.44mol L -1 g -1 VO of (2) 2+ The method comprises the steps of carrying out a first treatment on the surface of the While sc-bSPI-14 film produced lower VO 2+ Concentration of (0.41 mol L) -1 g -1 ) The sc-bSPI-14 film was demonstrated to have more excellent chemical stability.
In the above examples, the raw materials were all commercially available products except that 4,4',4", 4'" (5, 5 '-benzimidazole-2, 2') -tetraaniline and 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene were autonomously synthesized in the laboratory.
Wherein, fluorine-containing 'Y' -shaped branched triamine monomer: the synthesis procedure of TFAPOB is as follows:
(1) 4.2g of phloroglucinol, 20.73g of potassium carbonate, 22.55g of 2-chloro-5-nitrobenzotrifluoride, 200mL of DMAc and 20mL of toluene were sequentially added to a 500mL three-necked flask under nitrogen. The reaction system is stirred for 0.5h at normal temperature to fully dissolve solid substances, and then the temperature is raised to 80 ℃ for reaction for 12h. After the reaction is finished, pouring the liquid into deionized water, precipitating and precipitating, washing the precipitate by using deionized water, and vacuum drying the precipitate at 80 ℃ for 24 hours to obtain the 1,3, 5-tris (2-trifluoromethyl-4-nitrophenoxy) benzene solid powder.
(2) 16.35g of 1,3, 5-tris (2-trifluoromethyl-4-nitrophenoxy) benzene, 3.77g of activated carbon, 0.37g of FeCl 3 ·6H 2 O and 150mL of absolute ethanol were added sequentially to a 500mL three-necked flask. Firstly, the reaction system is heated to 80 ℃ and stirred for reaction for 0.5h to activate the activated carbon, and then the reaction system is cooled to 70 ℃. Subsequently, 50mL of hydrazine hydrate was slowly added dropwise to the reaction system using a constant pressure dropping funnel, and the reaction was continued for 12 hours. After the reaction is finished, repeatedly filtering while the solution is hot to completely remove the active carbon, pouring the obtained filtrate into deionized water, and standing for two days to obtain precipitate. Finally, filtering, collecting the precipitate, washing the precipitate with deionized water, and vacuum drying the washed precipitate at 60 ℃ for 24 hours to obtain the white fluorine-containing Y-type branched triamine monomer: TFAPOB.
The synthesis of 4,4' (5, 5' -benzimidazole-2, 2 ') -tetraaniline is as follows:
will be 14.02g P 2 O 5 And 50g of polyphosphoric acid were poured into a mechanically stirred three-necked flask and the temperature was raisedTo 180 ℃ to completely dissolve P 2 O 5 . Then cooling the three-mouth bottle to 80 ℃, adding 8.57g of 3,3 '-diaminobenzidine into the three-mouth bottle, heating to 120 ℃ until the 3,3' -diaminobenzidine is completely dissolved, then cooling to 80 ℃, finally adding 12.17g of 3, 5-diaminobenzoic acid into the three-mouth bottle, respectively stirring for 2,4 and 24 hours at 120,150 and 180 ℃, cooling to 80 ℃ after the reaction is finished, and finally pouring the mixture into deionized water, wherein the pH value is adjusted to 8.0 to remove polyphosphoric acid; the solid is obtained by filtration, washed by deionized water for a plurality of times, and dried in vacuum at 40 ℃ to obtain the X-type tetramine monomer containing imidazole groups: and BTA.
In the above embodiments, the amount of the substance may be converted into a mass; the mass units may be grams or kilograms.
The present invention and the embodiments described above are not specifically described in the prior art.
In the above examples, the process parameters (temperature, time, concentration, etc.) and the amount of each component in each step are within the ranges, and any point is applicable.
Although embodiments of the present invention have been disclosed above, it is not limited to the details and embodiments shown and described, it is well suited to various fields of use for which the invention would be readily apparent to those skilled in the art, and accordingly, the invention is not limited to the specific details and illustrations shown and described herein, without departing from the general concepts defined in the claims and their equivalents.
Claims (5)
1. A method for preparing a branched-crosslinked sulfonated polyimide film, comprising the steps of:
step one, under the protection of nitrogen, adding 1,4,5, 8-naphthalene tetracarboxylic anhydride, benzoic acid and m-cresol I into a reactor, and stirring and dissolving at room temperature; adding 2,2' -disulfonic acid benzidine, triethylamine and m-cresol II into a container, stirring at 50-70 ℃ until the materials are dissolved, and then adding
Sequentially adding 4,4' -diaminodiphenyl ether and 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene into a container, stirring at 50-70 ℃ until the materials are dissolved, then placing the materials in the container into a constant-pressure dropping funnel, dropwise adding the materials into a reactor, and stirring at 30-100 ℃ for reacting for 4-8 hours after the dropwise adding is completed to obtain a casting solution; pouring the casting solution on a dry and clean glass plate, casting the casting solution into a film, then drying the glass plate at 60-80 ℃ for 10-24 h, and then drying the glass plate at different temperatures of 80-150 ℃ for 0.5-3 h to obtain a triethylamine type branched-crosslinked sulfonated polyimide film;
or stirring and reacting for 1-2 hours at 30-100 ℃ after the dripping is completed to obtain a casting solution, placing the casting solution into a microwave-ultrasonic integrated reactor, and simultaneously starting microwaves and ultrasonic waves to perform cooperative treatment for 30-45 min, wherein the microwave power is 150-350W; the ultrasonic power is 300-800W, the ultrasonic frequency is 45-65 KHz, and the reaction temperature is 30-100 ℃; pouring the film casting solution after the cooperative treatment on a dry and clean glass plate for casting film, and then carrying out electron beam irradiation with the irradiation dose of 4-10 Gy; drying the glass plate in an infrared drying oven for 6-8 hours, wherein the power is 800-1000W, and the temperature is 50-60 ℃; then drying for 0.5-3 hours at different temperatures of 80-150 ℃ to obtain a triethylamine branched-crosslinked sulfonated polyimide film;
step two, placing the triethylamine type branched-crosslinked sulfonated polyimide film in absolute ethyl alcohol to soak 18-48 and h, and then placing the film in 1.0-3.0 mol L -1 Soaking in sulfuric acid aqueous solution for 24-48 h, then washing with deionized water for 5-10 times to obtain the branched-crosslinked sulfonated polyimide film, and soaking in deionized water for preservation.
2. The method of making a branched-crosslinked sulfonated polyimide membrane according to claim 1, wherein said
The molar ratio of 4,4 '-diaminodiphenyl ether, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 1,3, 5-tris (2-trifluoromethyl-4-aminophenoxy) benzene, 2' -disulfonic acid benzidine and benzoic acid is: 0.06-0.14:0.07-0.23:1:0.1:0.5:2.
3. The method for producing a branched-crosslinked sulfonated polyimide film according to claim 1, wherein said volume ratio of m-cresol I to m-cresol II is 1:1; the volume ratio of the total volume of the m-cresol I and the m-cresol II to the triethylamine is as follows: 20-70, 0.5-9.5; the dosage ratio of the triethylamine to the 2,2' -disulfonic acid benzidine is as follows: and each time 0.4-3.2 mmol of 2,2' -disulfonic acid benzidine is added, the volume of the added triethylamine is 0.5-9.5 mL.
4. The method for producing a branched-crosslinked sulfonated polyimide film according to claim 1, wherein said m-cresol i and m-cresol ii are each replaced with one or a mixture of two or more of N, N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, and N-methylpyrrolidone.
5. The method for preparing a branched-crosslinked sulfonated polyimide film according to claim 1, wherein said absolute ethyl alcohol is replaced with one or a mixture of two or more of methanol, acetone, isopropyl alcohol; the deionized water is replaced with distilled water or ultrapure water.
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