CN114597463A - A kind of preparation method and use of blend membrane based on microporous framework - Google Patents

Abstract

The invention discloses a preparation method and application of a microporous framework based blend membrane. The framework polymer is one of cyano-group PIM (PIM-1), oximido-group PIM (AO-PIM-1), carboxyl-group PIM (cPIM-1) and sulfonic-group PIM (sPIM-1), and the basal membrane is made of a non-fluorinated polymer with high proton conductivity. The invention provides a blending membrane strategy with simple preparation process and strong supporting framework for the first time, and effectively improves the mechanical stability of the ion-conducting membrane. On the one hand, the base film provides a large number of ion transport channels; on the other hand, the helical backbone polymer restricts the movement of the chains and thus improves the stability of the membrane. The mixing provides a new strategy for improving the service strength of the diaphragm.

Description

A kind of preparation method and use of blend membrane based on microporous framework

technical field

The invention relates to a preparation method and application of a microporous framework-based blended membrane, and belongs to the technical field of vanadium redox flow batteries.

Background technique

Vanadium redox flow batteries (VRFBs), as a large-scale energy storage technology, have been proven to be effectively utilized due to their environmental friendliness, high efficiency, adjustable power and capacity, long cycle life, and low maintenance costs. Renewable energy with intermittent characteristics, proton exchange membrane (PEM) not only plays the role of separating the positive and negative electrolytes, but also provides a channel for proton transport. It is one of the overall important components in the VRFB system, and its performance will Greatly affects the performance of the battery system. Currently, the most commonly used sulfonic acid-based separators have excellent proton conductivity and excellent stability, but their high vanadium ion permeability, low mechanical strength, and high fabrication cost severely limit their further development. Therefore, it is necessary to develop a new generation of high-performance PEMs for VRFBs.

Adding backbone polymers is one of the effective ways to enhance the stabilization ability of PEM. The selection of organic polymeric framework materials can well avoid the problem of interfacial compatibility caused by inorganic fillers. At the same time, this method can further modify the selected materials according to actual needs for better application. So far, materials such as PTFE, ePTFE, and PBI are used to prepare high-performance PEM, but most of these reinforced skeleton materials are hydrophobic materials, which will greatly sacrifice the proton conductivity of the material while hindering the penetration of vanadium ions.

SUMMARY OF THE INVENTION

The present invention provides a blended membrane for an all-vanadium redox flow battery, a preparation method and an application for the above-mentioned existing technical problems.

The purpose of the present invention can be achieved through the following technical solutions

A blended membrane based on microporous skeleton is characterized in that the blended membrane is based on sulfonated non-fluorine material, and a rigid helical skeleton polymer is mixed into it as a supporting material, and the supporting material is made of hydrophilic Inherently microporous polymer composition.

In the technical scheme of the present invention, the base film is composed of one or more of sulfonated polyether ether ketone, sulfonated polyimide, sulfonated polybenzimidazole, and sulfonated polyether sulfone.

In the technical solution of the present invention, the hydrophilic inherent microporous polymers are cyano PIM (PIM-1), oxime PIM (AO-PIM-1), carboxyl PIM (cPIM-1), sulfonic acid PIM (sPIM- 1) one or more of the composition;

Preferably: the method for synthesizing PIM-1 is to combine 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindole , tetrafluoroterephthalonitrile and solvent are mixed evenly, the mixture is heated at 50～500℃ for 3～8 hours, potassium carbonate is added during the reaction, washed after the reaction, recrystallized and dried to obtain PIM-1 powder ;

Preferred: Synthesis of cPIM-1: Mix PIM-1 with a solvent, add sodium hydroxide and stir, heat the mixture at 110-130°C for 5-9 d, cool down to room temperature after the reaction, wash and acid activation , cPIM-1 powder can be obtained after drying;

Preferred: Synthesis of sPIM-1: Add cPIM-1 to concentrated sulfuric acid, mix and stir, pour into purified water and wash to neutrality, and then dry to obtain sPIM-1;

Optimal: Synthesis of AO-PIM-1: Mix the powder of PIM-1 with tetrahydrofuran and react at 60-70°C for 18-22 hours. During the reaction, the nitrogen protection device is always open and hydroxylamine is added dropwise. After the reaction is completed, filter and dry. AO-PIM-1 powder was obtained.

In the technical solution of the present invention, the weight ratio of the hydrophilic inherent microporous polymer in the blend membrane is 0.1-50%, preferably 1-30%.

In the technical solution of the present invention, the thickness of the blended film is 10-100 μm.

In the technical scheme of the present invention, the synthesis of PIM-1: 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl with a mass of 1～5:1～5 -1,1'-Spirobiindole and tetrafluoroterephthalonitrile were evenly mixed with the solvent, the mixture was heated at 40-550°C for 4-6 hours, potassium carbonate was added during the reaction, and after cooling to room temperature, the mixture was poured in turn. Washed in water, recrystallized and dried to obtain PIM-1 powder; synthesis of cPIM-1: PIM-1 was added to the solvent and sodium hydroxide was added, followed by stirring, and the mixture was heated at 110-130 ° C for 6-8 d ; After cooling to room temperature, washing, acid activation treatment, and drying to obtain cPIM-1 powder.

An above-mentioned preparation method based on a microporous skeleton blended membrane, the steps of the method are: preparing a rigid helical skeleton polymer solution, preparing a sulfonated non-fluorine material solution; mixing the rigid helical skeleton polymer solution and the sulfonated non-fluorine material After the solution was mixed, it was cast in a petri dish and air-dried to obtain a blended membrane.

In the above method, the solvents in the rigid helical skeleton polymer solution and the sulfonated non-fluorine material solution are N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethylformamide One or more of sulfoxide (DMSO) are mixed.

In the above method, vacuum drying is adopted after blast drying, the drying temperature is 30-150°C, and the drying time is 10-15h.

In the above method, the following steps are included: the blended membrane is soaked in an acid solution for activation treatment; preferably, the acid solution is a 0.1-4M sulfuric acid solution.

In the technical scheme of the present invention: the application of the microporous framework blended membrane as a blended membrane of an all-vanadium redox flow battery.

In some embodiments, the hydrophilic inherently microporous polymer is a cyano-based PIM (PIM-1), an oxime-based PIM (AO-PIM-1), a carboxyl-based PIM (cPIM-1), a sulfonic acid-based PIM (sPIM- 1) It is used to improve the mechanical strength of the blend film, inhibit the swelling rate and improve the Coulombic efficiency.

Beneficial effects of the present invention:

The rational incorporation of porous PIMs material into the proton exchange polymer in the present invention can improve the performance of the resulting hybrid membrane, including the ability to optimize the vanadium barrier properties of the separator and improve the stability, thereby developing a new generation of high-performance PEM for the application of VRFB systems . In the present invention, by adding PIMs materials with different hydrophilic groups into the polymer substrate, the relative properties of the blend film VRFB can be respectively improved. The present application greatly enhances the vanadium-blocking properties of the films by introducing PIMs materials, thereby increasing the Coulombic efficiency (CE).

Description of drawings

Figure 1 is a) nuclear magnetic spectrum of PIM-1 and b) infrared images of PIM-1 and cPIM-1. c) BET test spectra of PIM-1 and cPIM-1 and d) thermogravimetric spectra of cPIM-1 and SPEEK.

Figure 2 is a digital photograph of a) cPIM/SPEEK-X casting solution image, b) cPIM/SPEEK-X diaphragm image and c) cPIM/SPEEK-X infrared spectrum (X = 0, 5, 10, 15, 20 ,25,30%).

Figure 3 is the cPIM/SPEEK-X cross-sectional electron microscope image (X=0, 5, 10, 15, 20, 25, 30%).

Figure 4 is a) tensile strength of cPIM/SPEEK-X, b) water absorption and swelling ratio, c) vanadium ion permeation curve and d) proton conductivity and ion-selective water absorption and swelling ratio (X=0,5 ,10,15,20,25,30%).

Figure 5 shows the performance of the all-vanadium flow battery a) schematic diagram of the flow battery, b) CE, c) VE, d) EE at current densities of 20-240 mA cm-2.

Figure 6 is a graph showing the performance of sPIM/SPEEK-X separator in an all-vanadium redox flow battery

Detailed ways

Below in conjunction with embodiment, the present invention is further described, but protection scope of the present invention is not limited to this:

Example 1 Preparation of PIM-1

Synthesis of PIM-1: 5.00 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindole (CAS: 77- 08-7, TTSBI) and 3.00g of tetrafluoroterephthalonitrile were added to a 250mL three-necked flask, then 100mL of DMF solution was added, added and mixed well, the mixture was heated at 150°C for 5 hours, and 4.2292g was added during the reaction. Potassium carbonate. After cooling to room temperature, it was poured into water for washing, recrystallized with chloroform/methanol system for more than 3 times to remove impurities, and then vacuum-dried at 120 °C for 24 h to obtain PIM-1 powder, as shown in Figure 1(a).

Example 2 Preparation of cPIM-1

Synthesis of cPIM-1: 4.8g of PIM-1 prepared in Example 1 was added to a 250mL three-necked flask, then a mixed solution of 100mL of water and ethanol (mass ratio 1:1) was added, and 40g of sodium hydroxide was added and stirred , the mixture was heated at 120 °C for 7 d. After completion, it was cooled to room temperature, washed with water for several times to remove impurities, and finally activated with 1M hydrochloric acid solution, and then vacuum-dried at 120 °C for 24 h to obtain cPIM-1 powder, as shown in Figure 1(b) and Figure 1(c).

Example 3 Preparation of sPIM-1

Synthesis of sPIM-1: 2 g of cPIM-1 prepared in Example 2 was added to 20 mL of concentrated sulfuric acid with a mass-to-volume ratio of 1:10 (the mass of cPIM-1 was 1, and the volume of concentrated sulfuric acid was 10), and after mixing and stirring for 24 h It was poured into purified water and washed to neutrality, and then vacuum-dried at 120 °C for 24 h to obtain sPIM-1.

Example 4 Preparation of AO-PIM-1

Synthesis of AO-PIM-1: Weigh 4.8g of the PIM-1 powder prepared in Example 1, dissolve it in tetrahydrofuran, pour it into a three-necked flask, heat it to 65°C and react for 20h. During the reaction, the nitrogen protection device is normally open and 50mL of hydroxylamine solution is added dropwise. (CAS: 7803-49-8). After the reaction was completed, the mixture was poured into 1 L of ethanol and the solid was collected by filtration. AO-PIM-1 powder was obtained by vacuum drying at 120 °C for 24 h.

Example 5 Preparation of cPIM-1/SPEEK blend film

SPEEK was prepared by sulfonation of PEEK in sulfuric acid (98wt.%) at 50℃ for 10h, and the sulfonation degree of SPEEK was 0.98. The cPIM-1/SPEEK blend films were then prepared by the following method.

1 g of cPIM-1 powder and 1 g of SPEEK were dissolved in 50 mL of dimethyl sulfoxide, respectively. Then, 12.5 mL of SPEEK solution and 6.25 mL of cPIM-1 solution were weighed and mixed according to the mass of each membrane (0.25 g). The new mixture was stirred for 24 hours and sonicated for 2 hours to form a homogeneous cPIM-1/SPEEK-5 mixture. Pour the prepared mixture in a petri dish. After the setting operation was performed in a 60°C oven for 2 hours, it was moved to a 120°C vacuum oven to dry for 12 hours. After drying, the membrane was soaked in 1M sulfuric acid solution for activation treatment. The activated membrane was immersed in pure water for preservation. The configured blend membrane is denoted as cPIM/SPEEK-X, where X represents the mass ratio of cPIM-1 and the membrane as a whole.

Figure 2 is a digital photograph of a) cPIM/SPEEK-X casting solution image, b) cPIM/SPEEK-X diaphragm image and c) cPIM/SPEEK-X infrared spectrum (X = 0, 5, 10, 15, 20 , 25, 30%). Figure 3 is a cross-sectional electron microscope image of cPIM/SPEEK-X (X=0, 5, 10, 15, 20, 25, 30%). With the increase of cPIM-1 content, the corresponding image 3(a), 3(b), 3(c), 3(d), 3(e), 3(f), the film thickness of the prepared blend films was 70 μm. The cross-section of the septum showed more folds that were evenly distributed over the entire cross-sectional area. It shows that the compatibility between cPIM-1 and SPEEK is good and cPIM-1 can be dispersed uniformly.

testing method

Swelling and Water Absorption

The SR (swelling rate) and WU (water absorption rate) of the membrane are obtained by the following two equations, respectively:

where d and W are the diameter and mass of the membrane in wet and dry states, respectively.

Mechanical behavior

The mechanical properties of the membranes were obtained on a universal testing machine with a tensile speed of 5 mmmin ^-1 . The samples were cut into strips of 35 mm × 10 mm, and the surface of the wet film was wiped with water before testing. To reduce test error, three samples of each film were tested and the resulting data were averaged. The formula for calculating the tensile strength of the film samples is as follows:

In the formula, F _Max is the maximum tension; W and D are the width and thickness of the sample film, respectively.

Proton transfer rate

The membrane proton transport rate was measured on an electrochemical workstation (Solartron analytical 1470E+1260A) using AC impedance spectroscopy. The sample was sandwiched between two circular titanium sheets held in place with coin cell battery clips. The test frequency was between 10 ³ and 10 ⁶ Hz, and the AC amplitude was 5 mV. The proton transfer rate of the membrane was measured by the latest method of Prof. Li's team. The calculation formula is as follows:

where σ is the proton transfer rate of the membrane. L is the thickness of the sample. R is the resistance of the membrane. A is the effective area of the membrane, that is, the area of the titanium sheet.

The sheet resistance can be calculated by the following formula:

R _A =R×A

R _A is the sheet resistance.

Vanadium ion permeation rate and ion selectivity

Tested in an H-pair diffusion cell with an effective area of 1.77 ^cm2 . One side of the diffusion cell was filled with 50mL of 1.5MVOSO ₄ /3.0MH ₂ SO ₄ solution, and the other side of the diffusion cell was filled with the same volume of 1.5M MgSO ₄ /3.0MH ₂ SO ₄ solution to balance ionic strength and osmotic pressure, and in Magnetic stirring was used to reduce concentration polarization in the test. Every 24h in MgSO ₄ /H ₂ SO ₄ solution, measure the product, and measure the absorbance at 762nm with a UV-visible spectrophotometer. The concentration of VO ²⁺ was determined using a standard absorbance/concentration curve. The penetration rate of vanadium can be calculated using the following formula:

Wherein V _B is the volume of MgSO ₄ /H ₂ SO ₄ solution, which is 50ml in this experiment; C _B (t) is the concentration of VO ²⁺ ions in the MgSO ₄ /H ₂ SO ₄ solution at time t; C _A is VOSO ₄ /H The VO ²⁺ concentration in the ₂ SO ₄ solution can be regarded as a constant when the test time is not too long to simplify the calculation; A and L are the effective membrane area and membrane thickness, respectively; P is the permeation rate of vanadium ions.

Ion selectivity is defined as the ratio of proton transfer rate to ^VO permeation rate and is calculated as follows:

Basic characterization of membranes

The tensile strength test in Fig. 4(a) shows that doping the framework material cPIM-1 can improve the mechanical strength of the separator. In Fig. 4(b), the water absorption and swelling rate are both reduced. It can be seen that the framework material inhibits the movement and dispersion of the flexible chain. . Figure 4(c) The vanadium ion migration rate decreases significantly with the increase of doping amount, which supports the inhibition of bulk ion transport by backbone chains. Figure 4(d) Proton conductivity decreases but H/V ion selectivity increases.

Single cell performance

The performance of the VRFB was tested using a home-made flow battery system consisting of a single membrane (with an effective distance of 10.5 cm ² ), two carbon felt electrodes, two graphite plate current collectors and a pair of housings. A membrane separates the negative electrolyte (10ml 1.5M ²⁺ /V ³⁺ 3MH ₂ SO ₄ ) and the positive electrolyte (10ml 1.5M VO ²⁺ /VO ₂₊ 3MH ₂ SO ₄ ) and is sandwiched between the two electrode. For the charge-discharge tests, the cut-off voltages for charge and discharge were 1.7 V and 0.8 V, respectively, and the tested current densities were 40, 60, 80, 100, and 120 mA cm ⁻² . For the cycling test, a constant current density of 120 mA cm ^-2 was tested at the same cut-off voltage. During the test, nitrogen gas was used. Calculate the Coulombic Efficiency (CE), Voltage Efficiency (VE) and Energy Efficiency (EE) of the battery by the following formulas:

where C _d and C _c are the discharge capacity and charge capacity, respectively; _{Ed and E c are} the discharge energy and charge energy, respectively.

The VRFB performance of cPIM/SPEEK-X blend films was evaluated (under a range of current densities from 40 to 120 mA cm ^-2 ). As shown in Figure 5, (a) is a schematic diagram of the battery test. It can be seen from Figure (b) that by mixing cPIM-1, the coulombic efficiency of SPEEK membrane can be significantly improved and the vanadium ion permeability can be reduced, Figure (b) Figure (c) shows that although the voltage efficiency is slightly reduced, the energy efficiency does not change significantly. Considering the above cell line data, the incorporation of porous PIMs materials into polymers is indeed an effective way to develop high-performance PEMs in the energy field. way.

Test of vanadium ion permeability

Figure 6 is a graph of data of doped film cells with small doses of doped framework materials. (a) The Tuulomb efficiency shows that the ion blocking ability of the separator is also enhanced, and the efficiency maps of (b) and (c) show that the small dose of doping framework material has a significant effect on the improvement of the battery performance.

Claims (11)

1. A blending membrane based on microporous frameworks is characterized in that a sulfonated non-fluorine material is used as a base membrane, a rigid spiral framework polymer is mixed in the base membrane to be used as a supporting material, and the supporting material is composed of a hydrophilic inherent microporous polymer.

2. The microporous framework based blend membrane according to claim 1, wherein the base membrane is selected from one or more of sulfonated polyether ether ketone, sulfonated polyimide, sulfonated polybenzimidazole, and sulfonated polyether sulfone.

3. The microporous-framework-based blend membrane of claim 1, wherein the hydrophilic intrinsically microporous polymer is one or more of cyano-PIM (PIM-1), oximo-PIM (AO-PIM-1), carboxy-PIM (cPIM-1), and sulfo-PIM (sPIM-1);

preferably: uniformly mixing 5,5',6,6' -tetrahydroxy-3, 3,3',3' -tetramethyl-1, 1' -spirobiindole and tetrafluoroterephthalonitrile with a solvent, heating the mixture at 50-500 ℃ for 3-8 hours, adding potassium carbonate in the reaction process, washing after the reaction is finished, recrystallizing and drying to obtain PIM-1 powder;

preferably: synthesis of cPIM-1: mixing PIM-1 with a solvent, adding sodium hydroxide, stirring, heating the mixture at 110-130 ℃ for 5-9 days, cooling to room temperature after the reaction is finished, washing, performing acid activation treatment, and drying to obtain cPIM-1 powder;

preferably: synthesis of sPIM-1: adding cPIM-1 into concentrated sulfuric acid, mixing and stirring, pouring into purified water, washing to neutrality, and drying to obtain sPIM-1;

preferably: synthesis of AO-PIM-1: weighing the PIM-1 powder and tetrahydrofuran, uniformly mixing, reacting at 60-70 ℃ for 18-22 h, adding hydroxylamine dropwise in a nitrogen protection device during the reaction, and filtering and drying after the reaction is finished to obtain AO-PIM-1 powder.

4. The microporous-backbone-based blend membrane according to claim 1, wherein the weight ratio of the hydrophilic intrinsically microporous polymer in the blend membrane is 0.1 to 50%, preferably 1 to 30%.

5. The microporous skeleton-based blend membrane of claim 1, wherein the blend membrane has a thickness of 10 to 100 μm.

6. The microporous framework based blend membrane of claim 3, wherein the synthesis of PIM-1: uniformly mixing 5,5',6,6' -tetrahydroxy-3, 3,3',3' -tetramethyl-1, 1' -spirobiindole and tetrafluoroterephthalonitrile with a solvent in a mass ratio of 1-5: 1-5, heating the mixture at 40-550 ℃ for 4-6 hours, adding potassium carbonate in the reaction process, cooling to room temperature, then sequentially pouring into water for washing, recrystallizing and drying to obtain PIM-1 powder;

synthesis of cPIM-1: adding PIM-1 into a solvent, adding sodium hydroxide, stirring, and heating the mixture at 110-130 ℃ for 6-8 days; after the reaction is finished, cooling to room temperature, washing, carrying out acid activation treatment, and drying to obtain the cPIM-1 powder.

7. The preparation method of the microporous framework based blend membrane according to claim 1, which comprises the following steps: preparing a rigid spiral skeleton polymer solution, and preparing a sulfonated non-fluorine material solution; and mixing the rigid spiral skeleton polymer solution and the sulfonated non-fluorine material solution, pouring the mixture in a culture dish, and performing forced air drying to obtain the blend membrane.

8. The method for preparing the microporous framework based blend membrane according to claim 7, wherein the solvent in the solution of the rigid helical framework polymer and the solution of the sulfonated non-fluorine material is one or more of N, N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC) and Dimethylsulfoxide (DMSO).

9. The preparation method of the microporous framework based blend membrane according to claim 7, characterized in that after air-blast drying, vacuum drying is adopted, and the drying temperature is 30-150 ℃; the drying time is 10-15 h.

10. The preparation method of the microporous framework based blend membrane according to claim 7, which comprises the following steps: soaking the blended film in an acid solution for activation treatment; preferably: the acid solution is 0.1-4M sulfuric acid solution.

11. The microporous framework based blended membrane of claim 1, wherein the microporous framework based blended membrane is used as a blended membrane of an all-vanadium flow battery.

Images