CN114865032A - Carbon quantum dot modified anion exchange membrane and preparation method and application thereof - Google Patents

Carbon quantum dot modified anion exchange membrane and preparation method and application thereof Download PDF

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CN114865032A
CN114865032A CN202210481237.0A CN202210481237A CN114865032A CN 114865032 A CN114865032 A CN 114865032A CN 202210481237 A CN202210481237 A CN 202210481237A CN 114865032 A CN114865032 A CN 114865032A
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polysulfone
exchange membrane
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周守勇
李梅生
赵宜江
肖慧芳
张秀
毛恒洋
张艳
杨大伟
彭文博
钟璟
张琪
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Huaiyin Normal University
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Abstract

The invention discloses a carbon quantum dot modified anion exchange membrane and a preparation method and application thereof.A hydrothermal synthesis method is adopted, citric acid and ethylenediamine are used as raw materials to prepare carbon quantum dots, polysulfone is used as a polymer membrane substrate, flexible side chains are introduced through chloromethylation reaction and quaternization reaction, and the chloromethylated polysulfone is subjected to side chain modification to prepare a side chain type carbon quantum dot doped modified polysulfone anion exchange membrane; the modified carbon quantum dots are prepared by adjusting the hydrothermal synthesis time and temperature, polysulfone is selected as an organic polymer main chain, a material with high active groups is synthesized by using a chloromethylation reaction, the carbon quantum dots are grafted and modified by the polysulfone main chain through a quaternization reaction, and the carbon quantum dots are completely quaternized by further using trimethylamine to prepare the partially grafted carbon quantum dot doped and modified polysulfone anion-exchange membrane.

Description

Carbon quantum dot modified anion exchange membrane and preparation method and application thereof
Technical Field
The invention belongs to the technical field of ion exchange membranes, and particularly relates to a carbon quantum dot modified anion exchange membrane and a preparation method and application thereof.
Background
The problems of environmental pollution and the like caused by fossil energy consumption are increasingly and seriously troubling people, the current society gradually pursues green life to deal with the facing crisis, and meanwhile, the development of novel green clean energy is urgently needed. The Alkaline Fuel Cells (AFCs) are one of green clean fuels, the product in the operation process is only water, the recovery and the treatment are convenient, in addition, the reaction kinetics is fast under the alkaline condition, the electrode reaction efficiency is high, a non-noble metal catalyst is allowed to be used, the production cost is greatly reduced, and the fuel cells are ideal new green energy sources at present. Anion exchange membranes as one of the components of AFCs capable of sequestering OH - Transported from the anode to the cathode, is a support for the reaction catalyst, is fuel-insulated anda gas. Therefore, the AFCs can run smoothly without opening the anion exchange membrane, and in order for the AFCs to have good battery performance, the service performance of the anion exchange membrane must be continuously concerned. The anion exchange membrane as a medium for transmitting hydroxide ions must have good ion conductivity, can resist the corrosion of hydroxide ions in an alkaline environment, and must have excellent chemical stability so as to enable the anion exchange membrane to work stably in AFCs, but the anion exchange membrane is also a key factor for limiting the development of AFCs.
To overcome the above disadvantages, various strategies have been proposed for improving the performance of anion exchange membranes. The side chain modification is used as a common modification method, can design and adjust a molecular structure, optimizes the micro-phase separation form in a membrane, and improves the ion conduction performance and the alkali resistance stability. Chu et al synthesized two side-chain anion exchange membranes, namely, side-chain anion exchange membranes with alkyl spacer length and 1,2, 3-triazole group linkage, and explored the effect of the length of the organic alkyl chain and the side chain with/without triazole group linkage on membrane performance. The results of the research show that the triazole group on the side chain can provide more water/ion transmission sites. Besides, the degradation of the side chain type anion exchange membrane depends on the length of the side chain, the SN2 substitution of the short chain anion exchange membrane (containing triazole group and only methylene connecting the main chain and the functional group) under the high pH environment, and the hydrocarbon chain length (n)>2 and m>4) Anion exchange membrane of 1 HNMR test results show that only PPO main chain is hydrolyzed, which shows that longer side chain can relieve the degradation of the polymer film. Therefore, the proper side chain is selected to modify AEM, so that the effect of improving the alkali stability of the anion exchange membrane can be achieved.
The organic-inorganic modification method combines the advantages of different types of materials, and the structure of the anion exchange membrane can be skillfully designed. Many scholars use inorganic nano materials such as zirconium dioxide, silicon dioxide, carbon nano tubes, graphene, carbon nitride and the like to prepare ion exchange membranes, and the prepared membranes show excellent mechanical properties. Wang et al adopt sol-gel method to prepare a series of hybridization anion-exchange membranes with stable physicochemical properties and Si-C-O network structure, the mechanical strength is 25.37MPa, and the service performance of the anion-exchange membranes is improved to a certain extent. The carbon quantum dot is a zero-dimensional nano material, has a sphere-shaped inner core structure and strong fluorescence property. As the smallest member of the carbon nanometer material family, the size effect, the interface effect and the like are prominent. The method is characterized by comprising the following steps of atom doping, surface functionalization, polymer end capping, core-shell structure and other abundant carbon quantum dot surface modification means, so that the carbon quantum dot surface modification means becomes an ideal raw material for preparing the composite material.
At present, researches on the interaction between inorganic materials and side chains by combining side chain modification and organic-inorganic modification are rarely reported. Therefore, the carbon quantum dot-doped side chain type anion exchange ion exchange membrane is prepared by adopting nontoxic and stable carbon quantum dots as an inorganic filling material, adopting polysulfone with good thermal stability and high mechanical strength as a polymer membrane matrix and modifying the polymer membrane matrix. Meanwhile, a series of polysulfone anion exchange membranes partially grafted with carbon quantum dots with different contents are designed and prepared by grafting modification on the carbon quantum dots, and the influence of the grafted rigid inorganic material carbon quantum dots on the performance of the anion exchange membranes is researched.
Reference documents:
(1)Chu X,Liu J,Miao S,et al.Crucial role of side-chain functionality in anion exchange membranes:Properties and alkaline fuel cell performance[J].Journal of Membrane Science, 2021,625:119172；
(2)Li X,Tao J,Nie G,et al.Cross-linked multibl℃k copoly(arylene ether sulfone) ionomer/nano-ZrO2 composite anion exchange membranes for alkaline fuel cells[J].Rsc Advances,2014,4(78):41398-41410；
(3)Yang C,Chiu S,Kuo S,et al.Fabrication of anion-exchange composite membranes for alkaline direct methanol fuel cells[J].Journal of Power Sources,2012,199:37-45；
(4)Ahmed S,Ali M,Cai Y,et al.Novel sulfonated multi-walled carbon nanotubes filled chitosan composite membrane for fuel-cell applications[J].Journal of Applied Polymer Science,2019, 136(22):47603；
(5)Abouzari-Lotf E,Etesami M,Nasef M M.18-Carbon-Based Nan℃omposite Proton Exchange Membranes for Fuel Cells[M]//Carbon-Based Polymer Nan℃omposites for Environmental and Energy Applications.2018:437-461；
(6)Lu Y,Pan X,Li N,et al.Improved performance of quaternized poly(arylene ether ketone)s/graphitic carbon nitride nanosheets composite anion exchange membrane for fuel cell applications[J].Applied Surface Science,2020,503:144071；
(7)Yifu W,Dan W,Jilin W,et al.Preparation and characterization of a sol-gel derived silica/PVA-Py hybrid anion exchange membranes for alkaline fuel cell application[J].Journal of Electroanalytical Chemistry,2020,873:114342。
disclosure of Invention
In order to solve the defects of the prior art, the invention aims to prepare a carbon quantum dot doped side chain type anion exchange membrane by adopting carbon quantum dots as an inorganic filling material and polysulfone as a polymer membrane substrate through modification, and simultaneously prepare a part of grafted polysulfone anion exchange membranes with different carbon quantum dots contents through grafting modification of the carbon quantum dots so as to improve the ion conductivity and the alkali resistance stability of the anion exchange membrane.
In order to achieve the above object, the present invention adopts the following technical solutions:
a carbon quantum dot modified anion exchange membrane having a repeating unit structure as shown below:
Figure BDA0003627955440000031
wherein the black spheres represent carbon quantum dots and the dashed lines represent hydrogen bonds.
The preparation method of the carbon quantum dot modified anion exchange membrane comprises the following steps:
s1, performing chloromethylation reaction on a benzene ring on polysulfone to prepare chloromethylated polysulfone (CMPSf);
s2, carrying out quaternization reaction on chloromethyl on the chloromethylated polysulfone to prepare quaternized polysulfone (QPSf);
s3, preparing Carbon Quantum Dots (CQDs) by taking citric acid and ethylenediamine as raw materials and utilizing a hydrothermal synthesis method;
and S4, reacting the quaternized polysulfone and the carbon quantum dots in an organic solvent, coating the reaction product, drying, and performing ion exchange treatment to obtain the ion exchange membrane.
The chloromethylation reaction of the benzene ring on the polysulfone comprises the following steps:
(1) completely dissolving dried polysulfone in an organic solvent, and stirring to obtain a polysulfone solution;
(2) adding paraformaldehyde into a polysulfone solution, sequentially dropwise adding trimethylchlorosilane and anhydrous tin tetrachloride, and refluxing and stirring under a nitrogen atmosphere to obtain a mixed solution;
(3) adding a precipitator into the mixed solution, filtering, washing a product, and drying in vacuum to obtain chloromethylated polysulfone; the quaternization reaction comprises the following steps:
dissolving chloromethylated polysulfone in an organic solvent, and then adding 2- [2- (dimethylamino) ethoxy ] ethanol for reaction to obtain quaternized polysulfone;
the preparation method of the carbon quantum dot comprises the following steps: dissolving citric acid and ethylenediamine in water, carrying out hydrothermal reaction, and purifying and drying the product to obtain the carbon quantum dots.
In the chloromethylation reaction, the proportion of polysulfone, paraformaldehyde, trimethylchlorosilane and anhydrous tin tetrachloride is 3 g: 0.5-1.5 g: 5-15 mL: 0.05-0.1mL, the reaction temperature is 30-50 ℃, and the reaction time is 20-50 h; chloromethylated polysulfones and 2- [2- (dimethylamino) ethoxy groups in quaternization]The weight ratio of ethanol is 15-20: 1, the reaction temperature is 30-50 ℃, and the reaction time is 10-30 h; in the preparation of the carbon quantum dots, the raw material ratio of citric acid to ethylenediamine is 1 g: 0.2-0.5mL, the reaction temperature of 130-; 0.5-2 mol.L is adopted in the ion exchange treatment process -1 Soaking in NaOH solution; in step S4, the carbon quantum dots account for 0.5-2% by weight of the quaternized polysulfone.
CarbonThe quantum dot modified anion exchange membrane is characterized by having a repeating unit structure shown as follows:
Figure BDA0003627955440000041
wherein black spheres represent carbon quantum dots.
The preparation method of the carbon quantum dot modified anion exchange membrane comprises the following steps:
s1, carrying out chloromethylation reaction on the benzene ring on the polysulfone to prepare chloromethylated polysulfone (CMPSf);
s2, preparing Carbon Quantum Dots (CQDs) by taking citric acid and ethylenediamine as raw materials and utilizing a hydrothermal synthesis method;
and S3, reacting the chloromethylated polysulfone with the carbon quantum dots in an organic solvent, adding trimethylamine to perform complete quaternary amination reaction after the reaction is finished, coating the reaction product, drying, and performing ion exchange treatment to obtain the ion exchange membrane.
The preparation method of the carbon quantum dot modified anion exchange membrane comprises the following steps of performing chloromethylation reaction on a benzene ring on polysulfone:
(1) completely dissolving dried polysulfone in an organic solvent, and stirring to obtain a polysulfone solution;
(2) adding paraformaldehyde into a polysulfone solution, sequentially dropwise adding trimethylchlorosilane and anhydrous tin tetrachloride, and refluxing and stirring under a nitrogen atmosphere to obtain a mixed solution;
(3) adding a precipitator into the mixed solution, filtering, washing a product, and drying in vacuum to obtain chloromethylated polysulfone;
the preparation method of the carbon quantum dot comprises the following steps: dissolving citric acid and ethylenediamine in water, carrying out hydrothermal reaction, and purifying and drying a product to obtain carbon quantum dots;
the preparation method of the carbon quantum dot modified anion exchange membrane is characterized in that in the chloromethylation reaction, the proportion of polysulfone, paraformaldehyde, trimethylchlorosilane and anhydrous tin tetrachloride is 3 g: 0.5-1.5 g: 5-15 mL: 0.05-0.1mL, the reaction temperature is 30-50 ℃, and the reaction time is 20-50 h; in the preparation of the carbon quantum dots,the raw material ratio of citric acid to ethylenediamine is 1 g: 0.2-0.5mL, the reaction temperature is 220-300 ℃, and the reaction time is 8-15 h; 0.5-2 mol.L is adopted in the ion exchange treatment process -1 Soaking in NaOH solution; the weight percentage of the carbon quantum dots in the chloromethylation polysulfone is 0.5-2%.
The carbon quantum dot modified anion exchange membrane is applied to an ion exchange membrane fuel cell.
The invention has the advantages that:
(1) the invention adopts a hydrothermal synthesis method, takes citric acid and ethylenediamine as raw materials to prepare carbon quantum dots, takes polysulfone with good thermal stability and high mechanical strength as a polymer film matrix, flexible side chains are introduced through chloromethylation reaction and quaternization reaction, 2- [2- (dimethylamino) ethoxy ] ethanol is adopted to carry out side chain modification on the chloromethylated polysulfone to prepare the modified polysulfone anion exchange membrane doped with side chain type carbon quantum dots, the carbon quantum dots are introduced to enhance the interaction with the flexible side chains, the hydrophilic-hydrophobic micro-phase separation structure in the ion exchange membrane is effectively constructed, by adjusting the content of the hydrophilic carbon quantum dots, the function between the hydrophilic carbon quantum dots and the side chains is changed, thereby improving the ion conductivity and the alkali-resistant stability of the anion exchange membrane and playing a positive role in improving the water loading capacity;
(2) the method comprises the steps of preparing modified carbon quantum dots by adjusting the time and temperature of hydrothermal synthesis, selecting low-cost and high-performance polysulfone as an organic polymer main chain, synthesizing a material with high-activity groups by using a chloromethylation reaction, grafting the modified carbon quantum dots on the polysulfone main chain through an quaternary ammonification reaction, and further completely quaternizing the modified carbon quantum dots by using trimethylamine to prepare the partially grafted carbon quantum dot doped and modified polysulfone anion exchange membrane, wherein N is generated after the carbon quantum dots are grafted to the polysulfone main chain + And Cl - The modified carbon quantum dots are used as the support body of the ion-conducting group, so that the ion-conducting group can exist stably, and the mechanical property of the anion-exchange membrane can be effectively improved.
Drawings
FIG. 1 is a synthesis scheme in example 1 of the present invention;
FIG. 2 is a synthesis scheme in example 2 of the present invention.
FIG. 3 is a representation of CQDs in example 1 of the present invention: (a) a particle size distribution graph, photographs of a control sample (water) and CQDs under daily light and a 365nm wavelength ultraviolet lamp in an aqueous solution, (b) an XRD (X-ray diffraction) pattern;
FIG. 4 is an FTIR spectrum of CQDs in example 1 of the present invention;
FIG. 5 is an XPS map of CQDs in example 1 of the present invention: (a) a full spectrum, (b) a high resolution C1s spectrum, (C) a high resolution N1s spectrum, and (d) a high resolution O1s spectrum;
FIG. 6 shows the combination of PSf, CMPSf, QPSf and anion exchange membranes in example 1 of the present invention 1 H NMR chart;
FIG. 7 is a FTIR spectrum of PSf, QPSf and anion exchange membrane of example 1 of the present invention;
FIG. 8 is a control membrane and anion exchange membrane of example 1 of the present invention: (a) a photo under daily illumination, (b) a photo under a 365nm wavelength ultraviolet lamp, (c) a control membrane surface SEM image, and (d) an anion exchange membrane surface SEM image;
FIG. 9 is a SAXS spectrum of a control membrane (a) and an anion exchange membrane (b) in example 1 of the invention;
FIG. 10 is a graph of (a) water absorption rate, (b) swelling rate of the control membrane and anion exchange membrane at different temperatures in example 1 of the present invention;
FIG. 11 is a water contact angle of a control membrane and an anion exchange membrane in example 1 of the present invention;
FIG. 12 is (a) OH of control and anion exchange membranes at different temperatures in example 1 of the present invention - Electrical conductivity, (b) apparent activation energy;
FIG. 13 is a graph of (a) thermogravimetric curves, (b) mechanical properties of the control and anion exchange membranes of example 1 of the present invention;
FIG. 14 is a graph of the performance of a methanol/air (no carbon dioxide) fuel cell at 60 ℃ in example 1 of the present invention;
FIG. 15 is an FTIR spectrum of CQDs in example 2 of the present invention;
FIG. 16 is an XPS map of CQDs in example 2 of the present invention: (a) a full spectrum, (b) a high resolution C1s spectrum, (C) a high resolution N1s spectrum, and (d) a high resolution O1s spectrum;
FIG. 17 is a 1H NMR chart of PSf, CMPSf, QPSf and anion exchange membrane in example 2 of the invention;
FIG. 18 is a FTIR spectrum of PSf, QPSf and anion exchange membrane of example 2 of the present invention;
FIG. 19 is an XPS spectrum of PSf-0.7% CQDs of example 2 of the present invention: (a) full spectrum, (b) high resolution C1s spectrum, (C) high resolution N1s spectrum and (d) high resolution Cl2p spectrum;
FIG. 20 is (a) OH of control and anion exchange membranes at different temperatures in example 2 of the present invention - Electrical conductivity, (b) apparent activation energy;
FIG. 21 is a graph of (a) thermogravimetric curves and (b) mechanical properties of the control membrane and anion exchange membrane of example 2 of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and the embodiments.
Example 1
The preparation method of the carbon quantum dot doped modified side chain type anion exchange membrane comprises the following steps:
(1) preparation of chloromethylated polysulfone (CMPSf)
Completely dissolving 3g of dried polysulfone in 150ml of dichloromethane by using a mechanical stirrer, stirring for 30min at the rotating speed of 200rpm, weighing 1.0g of paraformaldehyde, adding the paraformaldehyde into the mixed solution, stirring for a period of time, sequentially weighing 8.3ml of trimethylchlorosilane and 0.086ml of anhydrous stannic chloride, dropwise adding, reacting the mixed solution at 40 ℃ under the protection of nitrogen, refluxing and stirring for 36 h; after the reaction is finished, the mixed solution is placed in ethanol for precipitation for 30min, a filter cake layer is formed on filter paper through suction filtration, and the precipitate is washed for a plurality of times by using ethanol to obtain a product. The product was dried under vacuum at 80 ℃ for 24h to obtain dry CMPSf;
(2) preparation of Carbon Quantum Dots (CQDs)
Weighing 1.0507g of citric acid in a clean beaker, adding 10ml of ultrapure water, fully stirring to dissolve the citric acid, transferring 0.335 ml of ethylenediamine, transferring the ethylenediamine to the inner liner of a reaction kettle, putting the inner liner of the reaction kettle into a matched stainless steel reaction kettle, covering the stainless steel reaction kettle, screwing, sealing, putting the stainless steel reaction kettle into a forced air drying oven, and reacting for 5 hours at 150 ℃; naturally cooling to room temperature along with the furnace to obtain liquid, namely aqueous solution containing carbon quantum dots; filtering the solution by adopting a polyether sulfone filter with the pore diameter of 0.22 mu m to remove large-particle substances, then dialyzing and purifying for 2 days by using a dialysis bag with the molecular weight cutoff of 3500Da to obtain pure carbon quantum dot aqueous solution, and freeze-drying for 24 hours to obtain carbon quantum dot powder;
(3) preparation of quaternized polysulfone (QPSf)
Dissolving the dried CMPSf in N, N-dimethylacetamide (DMAc), and stirring at 35 ℃ for 30min to form a 10 w/v% CMPSf/DMAc homogeneous solution; subsequently, DMEE was added to the CMPSf/DMAc solution (weight ratio of DMEE to CMPSf 1: 12) and stirred at 45 ℃ for 24h to prepare QPSf;
(4) preparation of side chain type anion exchange membranes (QPSf-CQDs)
Dispersing CQDs in DMAc by using an ultrasonicator (30% power) for 6min to form a uniform dispersion liquid; adding the CQDs dispersion liquid into quaternized polysulfone, ultrasonically stirring for 1h, transferring the dispersion liquid into an oil bath pan, continuously stirring for 4h at 40-50 ℃, degassing and defoaming the casting film liquid by using a water pump, pouring the casting film liquid onto a clean flat glass plate, pre-evaporating the solvent for 30min, and further removing the residual solvent at 80 ℃ under vacuum to obtain a transparent and flexible film; at room temperature with 1 mol. L -1 Performing ion exchange on NaOH solution for 24 hours, washing and soaking the solution for 24 hours by using deionized water to prepare a side chain type anion exchange membrane, which is named as QPSf-x-CQDs, wherein x is the doping amount of the CQDs and is respectively 0%, 0.5%, 0.7% and 1%, the synthetic route is shown in figure 1, and the anion exchange membrane has the structural formula:
Figure BDA0003627955440000071
example 2
The preparation method of the carbon quantum dot doped and modified partial grafting type anion exchange membrane comprises the following steps:
(1) preparation of chloromethylated polysulfone (CMPSf)
Completely dissolving 3g of dried polysulfone in 150ml of dichloromethane at 30 ℃ by using a mechanical stirrer, adding paraformaldehyde into a polysulfone/dichloromethane solution, sequentially dropwise adding trimethylchlorosilane and anhydrous tin tetrachloride, refluxing and stirring the mixed solution at 40 ℃ under a nitrogen atmosphere for 36 hours, standing the mixed solution in ethanol for 0.5 hour for precipitation, washing the precipitate for several times by using ethanol to obtain a product, and drying the obtained solid in a vacuum oven at 80 ℃ for 24 hours to obtain CMPSf;
(2) carbon Quantum Dot (CQDs) preparation
Weighing 1.0507g of citric acid in a clean beaker, adding 10ml of ultrapure water, fully stirring to dissolve the citric acid, transferring 0.335 ml of ethylenediamine, transferring the ethylenediamine to the inner liner of a reaction kettle, putting the inner liner of the reaction kettle into a matched stainless steel reaction kettle, covering the stainless steel reaction kettle, screwing, sealing, putting the stainless steel reaction kettle into a forced air drying oven, and reacting for 10 hours at 250 ℃; naturally cooling to room temperature along with the furnace to obtain liquid, namely aqueous solution containing carbon quantum dots; filtering the solution by using a polyethersulfone filter with the pore diameter of 0.22 mu m, and dialyzing for 2 days by using a dialysis bag with the molecular weight cutoff of 3500Da to obtain a pure carbon quantum dot aqueous solution; placing the solution in a refrigerator for freezing overnight, and then freeze-drying for 24h to obtain a carbon quantum dot solid;
(3) preparation of partially grafted anion exchange membranes (gQPSf-CQDs)
Dissolving dried CMPSf in N, N-dimethylacetamide (DMAc), and stirring at 35 ℃ for 0.5h to form a 10 w/v% homogeneous solution, resulting in gQPSf; dispersing CQDs in DMAc by using an ultrasonic crusher (with the power of 30%) for 6min to form uniform dispersion liquid, dropwise adding the CQDs dispersion liquid into the casting solution, placing the casting solution into an oil bath kettle, stirring for 24h at the temperature of 40-50 ℃ to complete partial grafting, and then dropwise adding a trimethylamine aqueous solution into the casting solution to ensure complete quaternization; after the reaction was completed, the casting solution was degassed and defoamed with a water pump and cast onto a clean flat glass plate, the solvent was pre-evaporated for 30min, and the residual solvent was further removed under vacuum at 80 ℃ to obtain a transparent and flexible film. At room temperature with 1 mol. L -1 Soaking in NaOH solution for 24h, and adding Cl - Conversion to OH - Washing and soaking the membrane for 24 hours by using deionized water to prepare a partial graft modified anion exchange membrane named gQPSf-x-CQDs, wherein x is the doping amount of the CQDs and is respectively 0 percent, 0.5 percent and 0.7 percent1%, the synthetic route is shown as figure 2, and the structural formula of the anion exchange membrane is as follows:
Figure BDA0003627955440000081
characterization and Performance testing
Test method
1. Water absorption (Water uptake, WU) and Swelling Ratio (SR)
The sample was dried under vacuum at 80 ℃ for 24h and weighed. Soaking in deionized water at 30, 40, 50 and 60 deg.C, taking out sample, quickly wiping off surface water, and weighing. WU of the film is calculated from the following formula:
Figure BDA0003627955440000082
wherein, Ww is the membrane mass in the wet state, and Wd is the membrane mass in the dry state.
The sample was dried under vacuum at 80 ℃ for 24h and dried. Soaking in deionized water at 30, 40, 50 and 60 deg.C, taking out sample, quickly wiping off surface water, and measuring its length. The SR of the film is calculated from the following formula:
Figure BDA0003627955440000091
where Lw is the membrane length in the wet state and Ld is the membrane length in the dry state.
2. Ion exchange capacity
IEC represents the amount of a substance containing conductive ionic groups per unit mass of the membrane, and the value is determined by acid-base titration: the weighed membrane was immersed in 30ml of 0.01 mol. L -1 HCl solution for 24 h. 0.01 mol.L phenolphthalein as indicator -1 Back titrating the HCl solution with NaOH, and obtaining the IEC value of the membrane by using a formula:
IEC＝(V a -V b )×C NaOH /W d
where Wd represents the mass of the dry film, Va represents the volume of the blank sample, Vb is the volume of NaOH solution consumed for the test, and CNaOH represents the concentration of the NaOH solution.
3. OH-conductivity
The ion conductivity of the anion exchange membrane is measured by adopting a two-electrode alternating current impedance method, the alternating current impedance of the membrane (6cm multiplied by 1cm) is measured by utilizing an electrochemical workstation, the frequency range is set to be 0.01Hz-106Hz, the testing temperature is selected to be 30 ℃, 40 ℃, 50 ℃, 60, 70 and 80 ℃, and the ion conductivity of the membrane is calculated by the following formula:
σ＝L/RA
wherein, σ (mS. cm) -1 ) Represents the ionic conductivity, L (cm) represents the distance between the two electrodes, R (Ω) represents the AC impedance value of the membrane, and A (cm) 2 ) The cross-sectional area of the film is represented.
4. Cell performance
Constructing a direct fuel cell device, testing at 60 ℃, and hot-pressing a membrane electrode and platinum-loaded carbon paper at 60 ℃ and 2MPa to obtain the catalyst with the loading of 1 mg-cm- 2 (Pt/C). Mixing fuel (2 mol. L) -1 NaOH and 2 mol. L -1 Methanol mixed solution) at 2 ml/min -1 At a rate of 400 ml.min, humidified air -1 Is passed to the cathode during which the device is activated by heating at 60 c. And recording the relation curve of the potential on the membrane electrode along with the change of the current by using an electrochemical workstation.
(II) test results
1. Example 1 characterization of carbon quantum dots
CQDs are synthesized by hydrothermal reaction of citric acid and ethylenediamine, and FIG. 3 is a particle size distribution diagram of CQDs in an aqueous solution, from FIG. 3, it can be seen that the particle size of CQDs in an aqueous solution is about 4.07 nm. CQDs appear yellow under normal light and emit bright blue light under UV light. The crystallinity/amorphousness of CQDs was characterized and analyzed by XRD, and a broad peak around 26.2 ° was observed in the XRD spectrum of CQDs, indicating that CQDs are amorphous and consist of amorphous carbon in the inside.
To study the surface chemical structures of CQDsAnd performing FTIR characterization on the CQDs. FIG. 4 is an FTIR spectrum of CQDs, 3380cm, as shown in FIG. 4 -1 The nearby wide absorption band is the stretching vibration peak of O-H, 3260cm -1 2950cm of stretching vibration with nearby absorption band N-H -1 Near absorption band due to C-H stretching vibration, 1700cm -1 、1650cm -1 Nearby absorption band due to C ═ O stretching vibration, 1540cm -1 、1400cm -1 The nearby absorption band is due to C ═ C stretching vibration, 1170cm -1 1080cm of telescopic vibration with nearby absorption band of C-N -1 The nearby absorption band is caused by the stretching vibration of C-O-C, and the above results indicate that the prepared CQDs contain hydroxyl, carboxyl and amino on the surface.
To further confirm the results of FTIR analysis, XPS was used to determine the surface elemental composition and state of CQDs. The XPS spectrum, as shown in FIG. 5, shows that elements other than C, N, O were observed in the XPS spectrum, indicating that no impurities were introduced during the synthesis, and the peaks at 284.85, 400.18, and 531.87eV were C1s, N1s, and O1s, respectively. Elemental analysis showed that CQDs had 72.88% C atoms, 8.64% N atoms and 18.48% O atoms. The high resolution XPS spectrum of C1s shows three peaks at 284.81, 285.28, 287.92, and 288.68eV, corresponding to C-C, C-N, C-O, and C ═ O, respectively, as shown in fig. 5 (b). High resolution XPS spectra of N1s As shown in FIG. 5(c), the peak shown at 400.21 is due to N-H. The high resolution XPS spectrum of O1s shows two peaks at 531.84, 533.66eV due to C ═ O, C — O, as shown in fig. 5 (d). The results show that the prepared CQDs contain hydroxyl, carboxyl and amino on the surface, and are consistent with the result of FTIR analysis.
The characterization results show that the carbon quantum dots with the fluorescence effect and the hydroxyl, carboxyl and amino on the surface are successfully synthesized.
2. Chemical Structure characterization of PSf, CMPSf, QPSf and composite in example 1
To determine whether the synthesis of chloromethylated polysulfones, quaternized polysulfones and composite materials was successful, the process was carried out 1 H NMR and FTIR means, and analyzing the characterization results.
By using 1 H NMR characterization analysis of PSf, CMPSf and QPSf chemical structures, FIG. 6 is for PSf, CMPSf and QPSf 1 H NMR spectrum. The CMPSf spectrum showed a new characteristic peak at 4.53ppm compared to the unmodified PSf spectrum, due to chloromethyl-CH 2 The presence of chloromethyl on CMPSf was confirmed by the signal peak of H on Cl, and chloromethylated polysulfone was synthesized by chloromethylation reaction. By comparing CMPSf and QPSf spectrograms, chloromethyl-CH originally positioned at 4.5ppm can be subjected to quaternization modification 2 The characteristic peak of Cl basically disappears, and a new characteristic peak appears at 3.05ppm, which is a signal peak of H on the quaternary ammonium group. The above results indicate that chloromethyl groups are consumed during the Menshutkin reaction and that quaternized polysulfone was successfully synthesized.
According to the proportional relationship between the signal peak integral area of hydrogen in chloromethyl group and the signal peak integral area of hydrogen in unreacted methyl in the spectrogram, the chloromethylation degree of the polymer can be calculated by the following formula, namely, the average chloromethyl group introduced on each repeating structural unit.
Figure BDA0003627955440000111
In the formula, B is the integrated area of the signal at 4.53ppm and A is the integrated area of the signal at 1.70 ppm.
The chemical structures of PSf, QPSf and QPSf-0.7% CQDs were analyzed using FTIR characterization. FIG. 7 shows the infrared spectra of PSf, QPSf and QPSf-0.7% CQDs, which are 3350cm -1 Stretching vibration with nearby absorption band of O-H, 2970cm -1 Nearby stretching vibration with absorption band of C-H at 1582cm -1 And 1484cm -1 The two absorption bands are caused by asymmetric and symmetric stretching vibration of C ═ C in benzene ring of polymer, and are located at 1232cm -1 The nearby absorption band is caused by asymmetric stretching vibration of ether bond and is located at 1292cm -1 、1145cm -1 The absorption band in the vicinity is caused by asymmetric and symmetric stretching vibration of O ═ S ═ O, and the above is the basic structure of the polymer main chain PSf. The comparison of the spectra can find that the spectrum is positioned at 1620cm -1 To generate a new signalPeaks, due to quaternary ammonium groups, indicate successful grafting of quaternary ammonium groups onto PSf backbones.
3. Morphology and microstructure characterization of the side-chain anion exchange membranes in example 1
And performing morphological characterization analysis on the prepared anion-exchange membrane by using a camera and an SEM. Fig. 8 is a photograph under a daily light and an ultraviolet lamp of the control film and the anion exchange film, and it can be seen from fig. 8 that the prepared control film is transparent and the anion exchange film is transparent in yellow, which is caused by the yellow color developed by CQDs. The internal morphology of the AEM was visualized by SEM to see the internal morphology of the membrane. From FIG. 8, it can be seen that the membrane produced was uniform in surface and free of defects, indicating that a uniform, non-porous AEM was successfully produced.
And (3) analyzing and characterizing hydrophilic ion cluster domains in the QPSf control membrane and the anion exchange membrane by adopting SAXS. The size of the ion cluster is related to the q-value in SAXS. FIG. 9 is a SAXS diagram of a control membrane and an anion exchange membrane, from which FIG. 9 it can be seen that the control membrane and the anion exchange membrane are at 0.32nm, respectively -1 、0.29nm -1 A scattering peak appears indicating that significant microphase separation occurred within the membrane. The average space between the hydrophilic domains of the control membrane and the anion exchange membrane can be calculated to be 19.6nm and 21.6nm respectively according to a Bragg equation (d is 2 pi/qmax), which indicates that the hydrophilic domains in the membrane can be expanded to a certain extent by the existence of CQDs, and the transmission of hydroxyl ions is facilitated.
4. Example 1 Performance testing of side-chain anion exchange membranes
(1) Ion exchange capacity, water absorption, swelling ratio and hydrophilicity of QPSf-CQDs anion exchange membrane
The Ion Exchange Capacity (IEC) is expressed in terms of the number of ion conducting groups in the AEM. Higher values indicate more ion-conducting functions and groups available for transport within the membrane, and higher ion transport efficiency. The IEC values of the control membrane and the anion exchange membrane were calculated by the back titration method test, and the results are shown in Table 1, and the theoretical IEC formula:
IEC th ＝1000×DC/(M(PSf)+[M(CMPSf)-M(PSf)]×DC)
in the formula, DC represents the degree of chloromethylation, M(PSf) represents the molecular weight (442 g. mol) of the PSf repeating unit -1 )。
The data in the table 1 show that the IEC experimental value of the membrane is 1.06-1.37 mmol-g -1 Higher than the IEC value of 0.72 mmol.g of commercial Nafion115 -1 The prepared membrane has high ion transfer efficiency and can be used for fuel cells.
TABLE 1 WU, SR, IEC for control and side-chain anion exchange membranes
Figure BDA0003627955440000121
Water absorption is one of the important properties of AEM, reflecting the degree of membrane water loading. The higher the water absorption rate, the greater the loading indicating greater the degree of water absorption of the membrane, and the more hydronium ions in the membrane, the easier the transfer of hydroxide ions. And the increase of the water absorption rate inevitably causes corresponding swelling, and the mechanical property of the membrane is reduced. When swollen to some extent, the film loses flexibility and breaks. Therefore, the dimensional stability of the membrane is one of the key properties for continued use of AEM. The results of the water loading and swelling ratio at 30, 60 ℃ are shown in table 1 and are shown in fig. 10 with different temperature changes. As can be seen from the experimental results, the control membrane has a higher water loading, which is largely due to the pendant hydrophilic tail groups. Because the tail group is hydrophilic, the hydration process in the membrane is enhanced, and macroscopically, higher water loading is shown. Except for the QPSf-0.5 percent CQDs with lower IEC value, the water load and the swelling ratio of the anion exchange membrane are higher than those of a control membrane. The water absorption rate is improved from 27.9% of the control membrane to 35.6% of the anion exchange membrane. This is due to the introduction of hydrophilic CQDs within the membrane. CQDs are filled in the hydrophilic domain, so that the size of the hydrophilic domain is expanded, and the water loading capacity of AEM is improved. The water absorption and swelling ratio are increased with the temperature. The swelling ratio of the anion exchange membrane is 34.6% at the maximum at 60 ℃, which shows that the anion exchange membrane can keep better dimensional stability at 60 ℃.
To further confirm the effect of CQDs on the increase in AEM water loading, the hydrophilicity and hydrophobicity of AEM was evaluated by testing the water contact angle of the control membrane with the anion exchange membrane. Fig. 11 is a water contact angle of the control membrane and the anion exchange membrane, and it can be seen from fig. 11 that the water contact angles of the anion exchange membrane are all smaller than that of the control membrane (82.3 °), which indicates that the introduction of CQDs enables the membrane to attract more water molecules in the water environment, increases the water loading capacity, and improves the hydrophilicity of AEM. Meanwhile, as can be observed from fig. 11, the increase of the doping amount of the carbon quantum dots enables the water contact angle of the anion exchange membrane to be continuously reduced, and the minimum value can reach 76.4 degrees, which indicates that the carbon quantum dots can enhance the hydrophilicity of the membrane to a certain extent.
(2) QPSf-CQDs anion exchange membrane OH - Electrical conductivity of
The ion conductivity is the key performance of AEM, is the most direct expression of ion conductivity efficiency in the AEM, and shows the speed of the ion transmission rate, and the two are in direct proportion. The ionic conductivity of AEM is tested by adopting a two-electrode method, and the conductive ions are hydroxide ions. OH measured at different temperatures for control membrane and anion exchange membrane - The conductivity curve is shown in fig. 12. From FIG. 12, it can be seen that the QPSf-0.5% CQDs have a slightly lower conductivity than the control membrane. This is due to the slightly lower IEC value of QPSf-0.5% CQDs, the lower number of ion-conducting groups in the membrane, and the corresponding slower transmission rate of hydroxide ions. It is also observed from FIG. 12 that the doping levels were 0.7%, 1% anion exchange membranes were higher than the control membrane, QPSf-0.7% CQDs had conductivities as high as 42.03mS cm at 80 deg.C -1 . There are two main reasons for this: (1) number of ionic groups: the IEC value of the anion exchange membrane is slightly higher than that of the control membrane, and the quantity of ion conducting groups in the anion exchange membrane is more than that of the control membrane, so that the ion transmission can be accelerated, and the conductivity is improved; (2) effects of CQDs: the IEC of the QPSf-1% CQDs is equal to that of the control membrane, the two membranes have the same number of ion conducting groups, and the conductivity of the QPSf-1% CQDs is higher than that of the control membrane, which indicates that the introduction of the CQDs plays a role in accelerating the conduction. On one hand, the hydrophilic carbon quantum dots can play a role in expanding hydrophilic domains, and a hydrophilic/hydrophobic microphase separation structure is constructed; on the other hand, the surface of the hydrophilic carbon quantum dot is combined with water molecules and side chain tail groups to form hydrogen bonds, so that a hydrogen bond network structure is constructed, and more continuous stability is openedThe ion transport channel of (1). In a word, under the dual-strategy modification mechanism, the addition of the carbon quantum dots brings more activity space for hydroxide ions, widens ion channels and enables the hydroxide ions to smoothly run in the membrane.
The apparent activation energy is obtained using the following formula:
E a ＝-bR
in the above formula, b is the slope of a line fitted with ln σ and 1000/T, and R is the gas constant 8.314J (mol. K) -1 。
The Arrhenius pattern of the control membrane, anion exchange membrane, is shown in fig. 12. The apparent activation energy of the control membrane and the anion exchange membrane is calculated to be 6.88 to 11.01 kJ.mol -1 。
(3) Thermal stability and mechanical properties of QPSf-CQDs anion exchange membrane
The weight loss of AEM was tested under nitrogen using TGA to assess thermal stability during actual operation of AFCs. Figure 13 shows the weight loss of the control membrane versus the anion exchange membrane. The degradation of the membrane is mainly in the following three stages: the first stage is carried out at 30-210 ℃, and the weight loss is mainly caused by volatilization of water and a solvent adsorbed on the surface of the membrane material; the second stage is carried out at 210-390 ℃ and is caused by thermal decomposition of quaternary ammonium salt groups on a polymer chain; the third stage is carried out at 390-520 deg.C, which is caused by the thermal decomposition of the main chain of the polymer. In summary, since the actual operating temperature of AFCs is below 100 ℃, the anion exchange membrane can meet the thermodynamic requirements for fuel cell operation.
To investigate whether the prepared AEM satisfies the mechanical properties required for fuel cells, the tensile strength of the AEM at room temperature. The test results are shown in table 2, and it can be found from table 2 that the mechanical strength of AEM is between 24.0-31.7 MPa, and the mechanical properties of the anion exchange membrane are all higher than those of the control membrane, which is improved by 32% to the maximum, indicating that the prepared anion exchange membrane has good mechanical properties. Meanwhile, the Young modulus of AEM is 665-1034 MPa. The polymer film incorporating flexible side chains had good ductility, and it can be seen from the table that the elongation at break of the control film was as high as 67.5%, since the incorporation of a single C — O bond on the side chains was advantageous for enhancing the flexibility of the chains. However, the elongation at break of the anion exchange membrane is lower than that of the control membrane, which may be due to the fact that the rigid structure of the inorganic material is filled between the main polymer chain and the flexible side chain, and the movement of the chain is reduced, so that the flexibility of the anion exchange membrane is lower, but still kept at a normal level.
TABLE 2 mechanical Strength of control and side-chain anion exchange membranes
Figure BDA0003627955440000141
(4) Cell performance
And selecting a QPSf-0.7 percent CQDs anion exchange membrane with the highest conductivity for single cell testing. Using 2 mol. L - 1 NaOH and 2 mol. L -1 The performance of a methanol/air (no carbon dioxide) fuel cell at 60 ℃ using a mixed solution of methanol as a fuel is shown in fig. 14. As can be seen from fig. 14, the open circuit voltage of the fuel cell is 0.56V. The limiting current density at 60 ℃ is 22.29 mA cm -2 Has 4.52mW cm -2 The maximum power density of.
Compared with the anion exchange membrane of the same type, the power density is slightly lower. The reason is the following two aspects: firstly, the manufacturing method of the membrane electrode is diversified, and the simple and convenient hot-pressing platinum-loaded carbon paper method is adopted to prepare the membrane electrode. In the experimental process, the carbon paper loaded with the catalyst and the membrane are not tightly attached, so that certain resistance exists; secondly, influence factors in various aspects such as gas flow rate, feed liquid flow rate, operation temperature and the like need to be regulated and controlled in the operation process, so that certain errors occur in the performance of the single battery. Therefore, fuel cell process technology still needs to be improved to design a complete fuel cell system.
5. Example 2 characterization of carbon quantum dots
Analytical studies of the surface chemistry of CQDs were performed using FTIR. FTIR spectra of CQDs are shown in FIG. 15. As shown in FIG. 15, 3380cm -1 The wide absorption band of the vibration is O-H stretching vibration, 3075cm -1 Having an absorption band of N-HVibration at 2960cm -1 The absorption band of (B) is C-H stretching vibration. FTIR spectrum of carbon quantum dot prepared in comparative example 1 can find that 2500cm -1 The strength of the subsequent broad absorption peak is weakened, which shows that the hydroxyl, amino and carboxyl on the surface of the carbon quantum dot are reduced. This is because the degree of carbonization increases by changing the hydrothermal synthesis temperature and time. 1646cm -1 The absorption band of (B) is C ═ O, and the vibration is 1588, 1390cm -1 The absorption band of (A) is C ═ C stretching vibration, 1190cm -1 Stretching vibration with the absorption band of C-N.
To further determine the surface elemental composition and status of CQDs, XPS was used for test analysis. The XPS spectrum is shown in FIG. 16. Elements other than C, N, O were observed in the XPS spectrum, indicating that no impurities were introduced during the synthesis. The peaks at 284.8, 400.1 and 531.0eV are C1s, N1s and O1s, respectively. Elemental analysis showed that CQDs had a C atom content of 74.66%, a N atom content of 11.32%, and an O atom content of 14.02%. The high resolution XPS spectrum of C1s, as shown in fig. 13(b), shows three peaks at 284.80, 285.99, 287.32, 287.90eV, corresponding to C-C, C-N, C-O, C ═ O, respectively. The high resolution XPS spectrum of N1s showed 2 peaks at 399.69, 400.31eV as shown in FIG. 16(C), due to N- (C) 3 N-H. The XPS spectrum of the carbon quantum dot prepared in comparative example 1 revealed that N- (C) was generated 3 This may explain the change in the FTIR spectrum described above. The content of amino on the surface of the carbon quantum dot is reduced due to the increase of the carbonization degree, and the amino is gradually converted into N- (C) 3 And (5) structure. The structural transformation not only enhances the compatibility between organic and inorganic substances, but also is beneficial to grafting the surface of the carbon quantum dot to a polysulfone chain and enhancing the traction of a main chain to the carbon quantum dot. High resolution XPS spectra of O1s as shown in fig. 16(d), two peaks appeared at 531.06, 532.23eV due to the C ═ O, C — O groups. XPS and FTIR results show that the modified carbon quantum dots are successfully synthesized.
6. Chemical Structure characterization of PSf, CMPSf, QPSf and composite in example 2
By using 1 Characterization analysis was performed by H NMR nuclear magnetic resonance on PSf, modified polysulfone (CMPSf) and QPSf. FIG. 17 shows PSf and CMPSfQPSf nuclear magnetic hydrogen spectrum ( 1 H NMR) chart, comparing the PSf with the CMPSf chart, a new characteristic peak is found at 4.53ppm, and the peak is chloromethyl-CH 2 The presence of chloromethyl on CMPSf was confirmed by the signal peak for H on Cl, indicating the successful synthesis of chloromethylated polysulfone by chloromethylation reaction. By comparing CMPSf and QPSf spectra, chloromethyl-CH originally at 4.5ppm can be found 2 The Cl characteristic peak basically disappears, and a new characteristic peak appears at 3.05ppm, which is a signal peak of H on the quaternary ammonium group. The above results indicate that chloromethyl groups are consumed during the Menshutkin reaction, and the quaternized polysulfone is successfully synthesized.
Figure 18 shows FTIR plots of PSf, CQPSf and anion exchange membrane. 3357cm can be found by the spectrogram -1 The peak is the stretching vibration peak of O-H, 2968cm -1 The peak is C-H stretching vibration peak at 1582cm -1 And 1484cm -1 The two absorption bands are asymmetric and symmetric stretching vibration of C ═ C in a benzene ring in the polymer. At 1232cm -1 Asymmetric stretching vibration with absorption band of ether bond at 1292 and 1145cm -1 The absorption band at (a) is caused by the asymmetric and symmetric stretching vibrations of O ═ S ═ O. The above are the basic chemical structures of PSf. The spectrum of the PSf was compared with that of the control membrane and anion exchange membrane, and found to be 1617cm -1 New characteristic peaks are generated, caused by quaternary ammonium groups, indicating that the PSf backbone in the control membrane and anion exchange membrane has been successfully grafted with quaternary ammonium groups. The C-Cl is positioned in a fingerprint area, and the content is low, so that no obvious change exists on a spectrogram, and the judgment of successful grafting and elimination of a chloromethyl group is not facilitated.
To further investigate whether carbon quantum dots were successfully grafted to polysulfone backbone, characterization analysis of carbon quantum dot grafted polysulfones (PSf-0.7% CQDs) was performed using XPS. The XPS spectrum is shown in FIG. 19, and elemental analysis shows that the composite material contains 85.32% of C atoms, 1.51% of N atoms, 11.02% of O atoms and 2.16% of Cl atoms. The high-resolution XPS spectrum of N1s shows 3 peaks at 399.60, 400.67 and 402.03eV as shown in FIG. 19(C), and each represents N- (C) 3 、N-H、C-N + . ByThe nitrogen atoms in the composite material are all from carbon quantum dots, and the comparison of an N1s spectrogram of the carbon quantum dots can find that a new peak C-N appears + The result shows that the carbon quantum dots successfully react with the chloromethyl polysulfone to form the quaternary ammonium salt. At the same time, with N- (C) 3 The strong decrease in the N-H peak compared to the peak in (A) indicates that a portion of the N-H is consumed by the reaction. The results show that there is still a large amount of N- (C) 3 The structure is not reacted, and the site activity is probably low, which is not beneficial to the reaction. High-resolution XPS spectrum of Cl2p As shown in FIG. 19(d), peaks at 195.89, 198.66, 200.03 and 201.62eV respectively represent 2p 3/2 Cl - 、 2p 1/2 Cl - 、2p 3/2 C-Cl、2p 1/2 C-Cl. As can be seen from the spectrum of Cl2p, Cl - The appearance of (b) indicates that the quaternization reaction was successfully carried out. In addition, the presence of C-Cl indicates that the carbon quantum dots are partially grafted and the remainder can be completely quaternized with a tertiary amine such as trimethylamine.
7. Example 2 Performance testing of a partially grafted anion exchange Membrane
(1) gQPSf-CQDs anion exchange membrane OH - Electrical conductivity of
Ion conductivity is an important criterion for evaluating the ion transport performance of AEM, with higher values indicating faster ion transport rates within the membrane. The main factor affecting ion transport in AEM is the ion-conducting group. The anion can transit at the surface through the fixed ionic group, and the number of the conductive ionic groups affects the transmission site of the anion. OH measured at different temperatures for control membrane and anion exchange membrane - The conductivity is shown in fig. 20. From fig. 20, it can be seen that the gQPSf-0.5% CQDs anion exchange membrane has a conductivity comparable to the control membrane, and may not have a significant enhancement effect in the membrane due to too little doping of the carbon quantum dots. When the doping amount is 0.7 percent and 1 percent, the ion conduction performance of the anion exchange membrane is obviously superior to that of a control membrane, and OH - The maximum conductivity can reach 39.8mS cm -1 . The reason for this difference may be that the surface of the carbon quantum dot reacts with the main chain of the polymer to generate an ion-conducting group, which enhances the transport of ions in the membrane. And the two kindsThe conductivity of the membrane was kept at almost the same level, which may be that the active sites on the chloromethylpolysulfone may be saturated by reaction with the carbon quantum dot surface, the more active sites are completely consumed, and the remainder is fully quaternized by trimethylamine.
(2) Thermal stability and mechanical properties of gQPSf-CQDs anion exchange membrane
The thermal properties of AEM were tested under nitrogen using TGA to assess thermal stability during practical operation of AFCs. Figure 21 shows the weight loss of the control membrane versus the anion exchange membrane. The degradation of the membrane is mainly in the following three stages: the first stage is carried out at 30-170 ℃, and the weight loss is mainly caused by volatilization of water and a solvent adsorbed on the surface of the membrane material; the second stage occurs at 170-400 ℃ and is caused by thermal decomposition of quaternary ammonium salt groups on the polymer chain. In the interval, a contrast curve chart can find that the original control membrane with the lowest weight is changed into the control membrane with the highest weight to 400 ℃, and the content of quaternary ammonium groups in the control membrane is reflected from the side face to be lower than that of an anion exchange membrane, so that the grafting reaction of carbon quantum dots and a main chain is increased to guide the number of ion groups; the third stage is carried out at a temperature of 400-520 ℃ and is caused by thermal decomposition of the main chain of the polymer. The control membrane lost less weight than the anion exchange membrane, which was caused by the previous stage. Because the actual working temperature of the AFCs is lower than 100 ℃, the anion exchange membrane can meet the thermodynamic requirements of the AFCs.
In order to examine whether the membrane meets the mechanical requirements of the fuel cell, an electronic universal tester is adopted to test and analyze the membrane, and the analysis result is shown in table 3. As can be seen from Table 3, the mechanical strength of AEM is between 19.0 MPa and 35.4MPa, the mechanical strength of the anion exchange membrane is higher than that of a control membrane, and the highest improvement is 86%, which indicates that the introduction of the carbon quantum dots can significantly improve the mechanical performance of the membrane. Meanwhile, the Young modulus of AEM is 640-1053 MPa. Active sites provided on the polymer backbone immobilize carbon quantum dots, enhancing the rigidity of the polymer backbone. In addition, one or more main chains are grafted on the same carbon quantum dot, so that the structure in the membrane is compact, the action between the main chains of the polymers is enhanced, and the mechanical property of the anion exchange membrane is improved compared with that of a contrast membrane.
TABLE 3 mechanical Strength of control and partially grafted anion exchange membranes
Figure BDA0003627955440000171
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It should be understood by those skilled in the art that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by using equivalent alternatives or equivalent variations fall within the scope of the present invention.

Claims (9)

1. A carbon quantum dot modified anion exchange membrane is characterized by having a repeating unit structure shown as follows:
Figure FDA0003627955430000011
wherein the black spheres represent carbon quantum dots and the dashed lines represent hydrogen bonds.
2. The method of preparing the carbon quantum dot modified anion exchange membrane of claim 1, comprising the steps of:
s1, performing chloromethylation reaction on a benzene ring on polysulfone to prepare chloromethylated polysulfone (CMPSf);
s2, carrying out quaternization reaction on chloromethyl on the chloromethylated polysulfone to prepare quaternized polysulfone (QPSf);
s3, preparing Carbon Quantum Dots (CQDs) by taking citric acid and ethylenediamine as raw materials and utilizing a hydrothermal synthesis method;
and S4, reacting the quaternized polysulfone and the carbon quantum dots in an organic solvent, coating the reaction product, drying, and performing ion exchange treatment to obtain the ion exchange membrane.
3. The method for preparing the anion-exchange membrane modified by the carbon quantum dots according to claim 2, wherein the chloromethylation reaction of the benzene ring on the polysulfone comprises the following steps:
(1) completely dissolving dried polysulfone in an organic solvent, and stirring to obtain a polysulfone solution;
(2) adding paraformaldehyde into a polysulfone solution, sequentially dropwise adding trimethylchlorosilane and anhydrous tin tetrachloride, and refluxing and stirring in a nitrogen atmosphere to obtain a mixed solution;
(3) adding a precipitator into the mixed solution, filtering, washing a product, and drying in vacuum to obtain chloromethylated polysulfone;
the quaternization reaction comprises the following steps:
dissolving chloromethylated polysulfone in an organic solvent, and then adding 2- [2- (dimethylamino) ethoxy ] ethanol for reaction to obtain quaternized polysulfone;
the preparation method of the carbon quantum dot comprises the following steps: and dissolving citric acid and ethylenediamine in water, carrying out hydrothermal reaction, and purifying and drying a product to obtain the carbon quantum dots.
4. The method for preparing the carbon quantum dot modified anion-exchange membrane according to claim 3, wherein in the chloromethylation reaction, the ratio of polysulfone, paraformaldehyde, trimethylchlorosilane to anhydrous tin tetrachloride is 3 g: 0.5-1.5 g: 5-15 mL: 0.05-0.1mL, the reaction temperature is 30-50 ℃, the reaction time is 20-50h, and the precipitator is ethanol; chloromethylated polysulfones and 2- [2- (dimethylamino) ethoxy groups in quaternization]Weight ratio of ethanol15-20: 1, the reaction temperature is 30-50 ℃, and the reaction time is 10-30 h; in the preparation of the carbon quantum dots, the raw material ratio of citric acid to ethylenediamine is 1 g: 0.2-0.5mL, the reaction temperature of 130-; 0.5-2 mol.L is adopted in the ion exchange treatment process -1 Soaking in NaOH solution; in step S4, the carbon quantum dots account for 0.5-2% by weight of the quaternized polysulfone.
5. A carbon quantum dot modified anion exchange membrane is characterized by having a repeating unit structure shown as follows:
Figure FDA0003627955430000021
wherein black spheres represent carbon quantum dots.
6. The method for preparing the carbon quantum dot modified anion exchange membrane of claim 5, which is characterized by comprising the following steps:
s1, performing chloromethylation reaction on a benzene ring on polysulfone to prepare chloromethylated polysulfone (CMPSf);
s2, preparing Carbon Quantum Dots (CQDs) by taking citric acid and ethylenediamine as raw materials and utilizing a hydrothermal synthesis method;
and S3, reacting the chloromethylated polysulfone with the carbon quantum dots in an organic solvent, adding trimethylamine to perform complete quaternization after the reaction is finished, coating the reaction product, drying, and performing ion exchange treatment to obtain the ion exchange membrane.
7. The method for preparing the carbon quantum dot modified anion-exchange membrane according to claim 6, wherein the chloromethylation reaction of the benzene ring on the polysulfone comprises the following steps:
(1) completely dissolving dried polysulfone in an organic solvent, and stirring to obtain a polysulfone solution;
(2) adding paraformaldehyde into a polysulfone solution, sequentially dropwise adding trimethylchlorosilane and anhydrous tin tetrachloride, and refluxing and stirring in a nitrogen atmosphere to obtain a mixed solution;
(3) adding a precipitator into the mixed solution, filtering, washing a product, and drying in vacuum to obtain chloromethylated polysulfone; the preparation method of the carbon quantum dot comprises the following steps: and dissolving citric acid and ethylenediamine in water, carrying out hydrothermal reaction, and purifying and drying a product to obtain the carbon quantum dots.
8. The method for preparing the carbon quantum dot modified anion-exchange membrane according to claim 7, wherein in the chloromethylation reaction, the ratio of polysulfone to paraformaldehyde to chlorotrimethylsilane to anhydrous tin tetrachloride is 3 g: 0.5-1.5 g: 5-15 mL: 0.05-0.1mL, the reaction temperature is 30-50 ℃, the reaction time is 20-50h, and the precipitator is ethanol; in the preparation of the carbon quantum dots, the raw material ratio of citric acid to ethylenediamine is 1 g: 0.2-0.5mL, the reaction temperature is 220-300 ℃, and the reaction time is 8-15 h; 0.5-2 mol.L is adopted in the ion exchange treatment process -1 Soaking in NaOH solution; the weight percentage of the carbon quantum dots in the chloromethylated polysulfone is 0.5-2%.
9. Use of the carbon quantum dot modified anion exchange membrane of claim 1 or 5 in an ion exchange membrane fuel cell.
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