CN115395067A

CN115395067A - Acid-base blend membrane for proton exchange membrane fuel cell and preparation method thereof

Info

Publication number: CN115395067A
Application number: CN202211028377.9A
Authority: CN
Inventors: 王超; 申如星; 杨洁; 刘鑫; 郭艳艳; 童隆志
Original assignee: North University of China
Current assignee: North University of China
Priority date: 2022-08-25
Filing date: 2022-08-25
Publication date: 2022-11-25

Abstract

The invention discloses an acid-base blend membrane for a proton exchange membrane fuel cell, which is prepared by blending 85-95wt% of alkaline organic polymer PNBN and 5-15wt% of acidic organic polymer SPI.

Description

Acid-base blend membrane for proton exchange membrane fuel cell and preparation method thereof

Technical Field

The invention belongs to the technical field of membrane material preparation, relates to an acid-base blend membrane, and particularly relates to an acid-base blend membrane for a proton exchange membrane fuel cell and a preparation method of the acid-base blend membrane.

Background

A fuel cell is an electrochemical energy conversion device that can convert chemical energy of reactants directly into electrical energy. As global environmental and energy problems become more serious, new energy is urgently under development. Fuel cells, in turn, have proven to be capable of efficiently converting traditional fossil fuel energy sources into electrical energy due to their low or zero emissions.

Fuel cells can be classified into Proton Exchange Membrane Fuel Cells (PEMFCs), alkaline electrolyte fuel cells (AMFCs), molten Carbonate Fuel Cells (MCFCs), phosphoric Acid Fuel Cells (PAFCs), solid Oxide Fuel Cells (SOFCs), and the like, according to their operating temperature, cell components, and the type of electrolyte used. Among them, PEMFCs use hydrogen and oxygen as fuels, and have been widely used in the fields of aerospace, new energy vehicles, small electronic devices, and the like because of their advantages of environmental protection, easily available raw materials, and high energy efficiency.

The proton exchange membrane is a core component of the PEMFC, and plays a role in conducting protons and preventing gas permeation in the fuel cell.

The perfluorosulfonic acid membrane Nafion is a proton exchange membrane which is used more at present, has good mechanical property and chemical stability, and has high proton conductivity and high current density at low temperature. However, the membrane is easily degraded at high temperature, which leads to the decrease of proton conductivity and gas permeation resistance, and the cost is high, which limits the large-scale application of Nafion membrane in the field of fuel cell. Therefore, the development of a proton exchange membrane with low cost and high performance is an urgent task in the field of PEMFC.

CN 112216854A discloses an acid-base blend membrane for fuel cell and a preparation method thereof, which uses nadic anhydride and hexamethylene diamine to prepare polymer monomers, then the polymer monomers and the norbornene are subjected to ring-opening metathesis polymerization reaction to obtain a randomly polymerized alkaline organic polymer, the alkaline organic polymer is mixed with Nafion resin to obtain the acid-base blend membrane with higher ionic conductivity at high temperature, and the membrane cost is reduced by replacing the Nafion resin with a part of the alkaline organic polymer. However, the amount of the basic organic polymer in the acid-base blend membrane can only reach 10wt% at most, and not only is the size stability of the membrane material reduced due to excessive sulfonic acid groups, but also the reduction degree of the membrane cost is limited.

Therefore, the introduction of a new acidic organic polymer into the basic organic polymer is sought, and the method is an effective method for preparing the acid-base blending membrane with low cost and high performance.

Disclosure of Invention

The invention aims to provide an acid-base blend membrane for a proton exchange membrane fuel cell and a preparation method thereof.

The acid-base blend membrane for the proton exchange membrane fuel cell is prepared by blending 85-95wt% of alkaline organic polymer PNBN and 5-15wt% of acidic organic polymer SPI.

Wherein the basic organic polymer PNBN is a random polymer with a structure shown in the following formula (I), and the number average molecular weight is 160000-180000.

In the basic organic polymer PNBN, the molar ratio of two repeating units is p: q = 1: (1.5-2).

The acidic organic polymer SPI is a random polymer having a structure represented by the following formula (II) and has a number average molecular weight of 100000-150000.

In the acidic organic polymer SPI, the molar ratio m: n of two repeating units is = 1: (0.5-1.5).

Specifically, the acid-base blend membrane for the proton exchange membrane fuel cell has a structure represented by the following structural formula (III).

The invention further provides a method for preparing the acid-base blend membrane for the proton exchange membrane fuel cell, which comprises the steps of dissolving the alkaline organic polymer PNBN with the structure shown in the formula (I) in dichloromethane to obtain an alkaline organic polymer solution, dissolving the acidic organic polymer SPI with the structure shown in the formula (II) in N, N-dimethylformamide to obtain an acidic organic polymer solution, mixing the two solutions to obtain a mixed solution, casting the mixed solution to form a membrane, and drying to form the acid-base blend membrane.

It should be noted that the present invention provides a typical method for preparing the acid-base blend film, but not the only method.

More specifically, the invention mixes the alkaline organic polymer solution and the acidic organic polymer solution, then stirs for 2-3h at room temperature, then carries on ultrasonic treatment for 10-30min, finally stands for 10-30min to obtain the mixed solution.

The drying process for preparing the acid-base blending membrane is preferably vacuum drying at 30-40 ℃ for 2-3h, and then heating to 80-100 ℃ for vacuum drying for 12-15h.

The acid-base blend membrane for the proton exchange membrane fuel cell prepared by the invention is a brown thin membrane, is insoluble in water, has stable physicochemical properties, can meet the requirements of the proton exchange membrane fuel cell on the proton exchange membrane, and can be used as the proton exchange membrane of the fuel cell.

In the raw materials for preparing the acid-base blend membrane for the proton exchange membrane fuel cell, the basic organic polymer PNBN can be prepared into a polymer monomer by using nadic anhydride and 1, 6-hexamethylene diamine as raw materials according to the method provided in CN 112216854A, and then the polymer monomer and norbornene are subjected to ring-opening metathesis polymerization under the catalysis of a Grubbs 3rd catalyst to prepare a high polymer taking a norbornene structure as a main body.

Wherein, the ring-opening metathesis polymerization reaction of the alkaline organic polymer needs to be carried out in an inert atmosphere and a dry dichloromethane solution.

In the raw materials for preparing the acid-base blend membrane for the proton exchange membrane fuel cell, the acidic organic polymer SPI can react with 4,4' -diamino-2, 2' -disulfonic acid diphenyl ether and 4,4' -diaminodiphenyl ether and 1,2,4, 5-cyclohexane tetracarboxylic dianhydride respectively according to the method provided in CN 114437347A to obtain a prepolymerization solution, and then the two prepolymerization solutions are mixed for polymerization reaction to prepare a random polymer.

The acid-base blending membrane material prepared by the invention takes norbornene-based alkaline organic polymer as a matrix and is blended with sulfonated polyimide-based acidic organic polymer, the preparation method is simple, and compared with a commercialized Nafion membrane, the acid-base blending membrane material greatly reduces the production cost of the membrane material, so that the cost of a proton exchange membrane fuel cell is correspondingly reduced, and the acid-base blending membrane material has obvious advantages.

Furthermore, compared with a single alkaline organic polymer membrane, the acid-base blend membrane has higher ion exchange capacity, and the introduced acidic organic polymer contains sulfonic acid functional groups, so that the introduced acidic organic polymer can be used as proton transmission sites and can play a role in proton conduction.

Compared with a single alkaline organic polymer membrane, the acid-base blend membrane also has better mechanical property, the introduced acidic organic polymer not only has a rigid main chain, but also contains a sulfonic acid group which can interact with an alkaline group in the alkaline organic polymer to form a hydrogen bond network, and the two factors act simultaneously to improve the mechanical stability of the membrane material.

Compared with a single alkaline organic polymer membrane, the acid-base blend membrane has higher ionic conductivity and is obviously influenced by temperature.

A CCM method is adopted, the acid-base blend membrane prepared by the method is used for preparing a membrane electrode for testing in a proton exchange membrane fuel cell, and the result shows that the acid-base blend membrane has high open-circuit voltage and excellent power density, and the acid-base blend membrane has high gas permeation resistance and proton conductivity.

Drawings

Fig. 1 is an infrared spectrum of a basic organic polymer film and an acid-base blend film containing different mass fractions of an acidic organic polymer.

FIG. 2 is a surface and cross-sectional micro-topography of a basic organic polymer membrane and an acid-base blend membrane containing different mass fractions of an acidic organic polymer.

Fig. 3 is a graph of tensile strength and elongation at break for alkaline organic polymer membranes and acid-base blended membranes containing different mass fractions of acidic organic polymers.

Fig. 4 is a graph of water absorption, swelling ratio, and ion exchange capacity for a basic organic polymer membrane and an acid-base blend membrane containing different mass fractions of an acidic organic polymer.

Fig. 5 is a graph of ionic conductivity versus temperature for a basic organic polymer membrane and an acid-base blended membrane containing different mass fractions of an acidic organic polymer.

Fig. 6 is an open circuit voltage and power density for different current densities in a proton exchange membrane fuel cell for an alkaline organic polymer membrane and an acid-base blend membrane containing different mass fractions of an acidic organic polymer.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are provided only for more clearly illustrating the technical solution of the present invention so that those skilled in the art can well understand and utilize the present invention, and do not limit the scope of the present invention.

Unless otherwise specified, the production processes, experimental methods or detection methods related to the embodiments of the present invention are all conventional methods in the prior art, and the names and/or abbreviations thereof all belong to conventional names in the art, which are clearly and clearly understood in the related fields of use.

The various instruments, equipments, raw materials or reagents used in the examples of the present invention are not particularly limited in their sources, and are all conventional products commercially available from normal commercial sources, and can be prepared by conventional methods well known to those skilled in the art.

Example 1.

5g of nadic anhydride is weighed and completely dissolved in 40ml of acetic acid, then 10.63g of 1, 6-hexanediamine is added, and the mixture is condensed and refluxed for reaction for 3 hours at the temperature of 125-130 ℃ under the protection of Ar gas, so as to obtain yellow transparent solution.

And after the reaction liquid is cooled to room temperature, adding 40ml of dichloromethane and 40ml of deionized water, shaking for full extraction, standing, collecting a lower organic layer, and washing twice with deionized water to obtain a light yellow transparent solution.

Adjusting the pH value of the light yellow transparent solution to be alkalescent by using 1M NaOH solution, and washing the solution with 40ml of deionized water for three times by using anhydrous Na ₂ SO ₄ Drying and purifying the product by column chromatography to obtain the polymerized monomer of light yellow oil.

0.2712g of the polymerized monomers, 0.1946g of norbornene monomers, 0.0090g of Grubbs catalyst were weighed out separately and dissolved in 5ml of dry dichloromethane. Firstly, adding a polymerization monomer and a norbornene monomer into a reactor, degassing for three times, then adding a Grubbs catalyst, continuing degassing for three times, reacting for 0.5h under the atmosphere of Ar at the temperature of 30-40 ℃, and preparing the alkaline polymer PNBN solution after the reaction is finished.

Example 2.

0.40g of 1,2,4, 5-cyclohexanetetracarboxylic dianhydride and 0.66g of 4,4 '-diamino-2, 2' -disulfonic biphenyl were weighed in a flask, 10ml of m-cresol was added under an Ar atmosphere, after complete dissolution, 5ml of toluene and 0.5ml of isoquinoline were added, and reacted at 70-80 ℃ for 5h and 180 ℃ for 18h to obtain a first prepolymerization solution.

0.25g of 1,2,4, 5-cyclohexanetetracarboxylic dianhydride and 0.25g of 4,4' -diaminodiphenyl ether were weighed in a flask, 10ml of m-cresol was added under an Ar atmosphere to dissolve completely, 0.5ml of toluene and 0.5ml of isoquinoline were added, and the mixture was reacted at 70 to 80 ℃ for 5 hours and at 180 ℃ for 18 hours to obtain a second prepolymerization solution.

And mixing the first pre-polymerization solution and the second pre-polymerization solution, reacting at 175-185 ℃ for 18h to obtain a random polymer solution, pouring the random polymer solution into 400ml of ethyl acetate, and separating out a light yellow solid to prepare the acidic polymer SPI.

Example 3.

A PNBN solution was prepared according to the method of example 1 and cast directly to produce a basic polymer film free of acidic polymer.

Example 4.

0.0245g of SPI was weighed, added to 5ml of N, N-dimethylformamide, and sufficiently dissolved to form a red transparent solution, which was mixed with the PNBN solution prepared in example 1 and stirred for 2 hours, followed by ultrasonic treatment for 15min and standing for 10min to prepare a PNBN/SPI blended solution.

And (3) casting the blending solution in a clean and flat glass dish by adopting a solution casting method, drying at 30 ℃ for 3h and at 100 ℃ for 12h, and cooling to prepare the acid-base blending membrane with the acid polymer mass fraction of 5%.

Example 5.

A basic polymer PNBN solution was prepared by the method of example 1 by weighing 0.2434g of polymerized monomers and 0.1757g of norbornene monomers.

0.0465g of SPI is weighed and blended with the PNBN solution according to the method of the embodiment 3 to prepare the acid-base blended membrane with the acid polymer mass fraction of 10%.

Example 6.

A solution of the basic polymer PNBN was prepared by the method of example 1 while weighing 0.2426g of the polymerized monomer and 0.1838g of the norbornene monomer.

0.0735g of SPI is weighed and blended with the PNBN solution according to the method of example 3 to prepare the acid-base blended membrane with the acid polymer mass fraction of 15%.

FIG. 1 shows the IR absorption spectra of film materials prepared in examples 3, 4 and 5. 2850cm ^-1 And 2935cm ^-1 The absorption peak at (A) represents the methylene group (-CH) in the PNBN matrix ₂ -) C-H tensile vibration, likewise 1552cm ^-1 And 1400cm ^-1 The absorption peak at (a) is due to the N-H tensile vibration in the PNBN matrix. The characteristic absorption peak of the sulfonic acid functional group is 1249cm in the infrared spectrums of PNBN/SPI-5% and PNBN/SPI-10% ^-1 (O = S = O asymmetric stretching vibration), 1088cm ^-1 (O = S = O symmetric tensile vibration) and 1018cm ^-1 (S = O tensile vibration), while these absorption peaks were absent in PNBN/SPI-0%, indicating that acidic organic polymer SPI was successfully introduced into PNBN.

FIG. 2 shows Scanning Electron Micrographs (SEM) of the surfaces and cross sections of the membrane materials prepared in examples 3-6. As shown in fig. 2 (a) and (e), the PNBN/SPI-0% membrane material is single in composition, and the surface and cross-section of the membrane are compact and smooth, indicating that the membrane material has a uniform microscopic morphology. FIGS. 2 (b) and (f), (c) and (g), (d) and (h) correspond to surface and cross-sectional micro-morphologies of 5%, 10% and 15% of the membrane material, respectively, and it can be seen that there was no significant phase separation, indicating that the membrane material was homogeneous in texture, which can be attributed to the fact that SPI contained a hydrophilic group-SO ₃ H, PNBN contains-NH ₂ And two functional groups interact with each other, thereby showing good compatibility. Taken together, SEM results may indicate that PNBN was homogeneously mixed with SPI.

FIG. 3 is a graph showing the results of the dimensional stability and ion exchange capacity tests of the membrane materials prepared in examples 3-6. The water absorption rate (WU) and the Swelling Rate (SR) of the PNBN/SPI-0% membrane are the lowest, and both the WU and the SR of the membrane show a trend of increasing along with the addition of the SPI, which is mainly because sulfonic acid groups introduced by the SPI polymer are water-absorbing groups, and the water absorption and swelling phenomena of the membrane material are promoted. When the SPI content is increased from 5% to 10%, the increase of SR is not as obvious as WU, because although the introduced sulfonic acid groups are increased, the sulfonic acid groups and the matrix have amino interaction, the formed hydrogen bond helps the membrane material to keep a stable state, and the hydrogen bond formed between the amphoteric groups plays a main role in the process of swelling the membrane material. The Ion Exchange Capacity (IEC) of the membrane material also increases with the introduction of acidic organic polymers, which is mainly directly influenced by the increase in the number of sulfonic acid functional groups. Therefore, SPI is introduced into the PNBN matrix, and the stability and the ion exchange capacity of the membrane material can be effectively improved.

Fig. 4 shows the mechanical properties of the membrane materials of examples 3-6, in the fuel cell, the membrane materials are subjected to external environment such as tension and compression, and the proper mechanical properties are the properties that the membrane materials must have in order to ensure the stable operation of the fuel cell. The tensile strength of PNBN/SPI increases with increasing SPI, while the elongation at break is in the opposite trend. These two opposing trends are likely due to the blending-induced SPI rigid backbone that improves the mechanical properties of the blended membranes. On the other hand, the crosslinking structure between the sulfonic acid functional group and the nitrogen-containing group increases, and therefore, the more SPI in the blended film, the tighter the microstructure of the blended film. Overall, the prepared blend membrane with the added SPI can meet the requirements of a Proton Exchange Membrane Fuel Cell (PEMFC).

Fig. 5 and table 1 are the results of ionic conductivity (σ) tests for examples 3-6, σ for the prepared blend membranes was tested at 20, 40, 60, 80 ℃, respectively, and the results are shown in fig. 5. The results show that the ionic conductivity of the no-SPI membrane is lowest, while σ for the membrane increases with increasing SPI ratio. This can be attributed to the introduction of SPI providing more proton transport sites and hydrogen bonding networks formed by the acid-base functional groups contained in the two polymers, which allows better proton transport and they comply with the Vehicle and grotthus mechanisms, respectively. Meanwhile, the results of table 1 show that the higher the temperature, the higher the ionic conductivity of the blended membrane. As can be seen from the results, the membrane conductivity containing SPI is relatively much affected by temperature, mainly because polymer molecules move faster with increasing temperature, thereby accelerating the transport of protons. Therefore, the introduction of SPI in the PNBN matrix can effectively improve the electrochemical performance of the membrane material.

FIG. 6 shows the cell performance of the membrane materials prepared in examples 3, 5 and 6, and the Open Circuit Voltage (OCV) of the PNBN/SPI-0%, PNBN/SPI-10% and PNBN/SPI-15% membranes are all greater than 0.90V, indicating that the prepared polymer blends have higher hydrogen permeability. As the SPI ratio increases from 10% to 15%, the power density of the PNBN/SPI film is increased, due to the-SO of the SPI ₃ ^- -NH with PNBN ₂ Electrostatic interaction between them. Power density of 11.8mW cm with PNBN ^-2 Compared with PNBN/SPI-15%, the power density is higher due to good compatibility, and the power density reaches 104.3mW cm ^-2 . With commercial NaCompared with a fion membrane material, the membrane material prepared by the invention has lower cost on one hand, and the membrane material prepared by the invention can show better battery performance under lower ionic conductivity on the other hand. Thus, PNBN/SPI blend membranes are promising polymeric materials in PEMFC membranes.

The above characterization results show that, compared with PNBN/SPI-0%, the acid-base blending membrane can effectively solve the balance problem of electrochemical performance and dimensional stability due to the electrostatic interaction between acid-base groups. Thus, it can be seen that the electrochemical performance of examples 5 and 6 is significantly better than that of the soda organic polymer film, in particular, in that the power density is significantly higher than that of the soda organic polymer film.

The open circuit voltage of the acid-base blend membrane material prepared by the invention can reach 0.90V, which is slightly larger than that of blend membranes in other proportions, and the open circuit voltage shows that the membrane material can better prevent gas cross contamination, and simultaneously can still reach 104.3mW cm under the condition of lower ion exchange capacity ^-2 The power density of the invention has better electrochemical performance, and achieves the technical effect of the invention.

The above embodiments of the present invention are not intended to be exhaustive or to limit the invention to the precise form disclosed. Various changes, modifications, substitutions and alterations to these embodiments will be apparent to those skilled in the art without departing from the principles and spirit of this invention.

Claims

1. An acid-base blend membrane for proton exchange membrane fuel cell is prepared by blending 85-95wt% of alkaline organic polymer PNBN and 5-15wt% of acidic organic polymer SPI,

wherein the basic organic polymer PNBN is a random polymer having a structure represented by the following formula (I) and has a number average molecular weight of 160000 to 180000:

in the basic organic polymer PNBN, the molar ratio of two repeating units is p: q = 1: (1.5-2);

the acidic organic polymer SPI is a random polymer having a structure represented by the following formula (II) and having a number average molecular weight of 100000 to 150000:

in the acidic organic polymer SPI, the molar ratio of the two repeating units m: n is = 1: (0.5-1.5).

2. The acid-base blend membrane for proton exchange membrane fuel cells according to claim 1, having a structure represented by the following structural formula (III):

。

3. the preparation method of the acid-base blend membrane for proton exchange membrane fuel cell according to claim 1, which comprises the steps of dissolving the alkaline organic polymer PNBN with the structure shown in the formula (I) in dichloromethane to obtain an alkaline organic polymer solution, dissolving the acidic organic polymer SPI with the structure shown in the formula (II) in N, N-dimethylformamide to obtain an acidic organic polymer solution, mixing the two solutions to obtain a mixed solution, casting the mixed solution into a membrane, and drying to form the acid-base blend membrane.

4. The method according to claim 3, wherein the mixed solution is obtained by mixing the basic organic polymer solution and the acidic organic polymer solution, stirring at room temperature for 2 to 3 hours, further performing ultrasonic treatment for 10 to 30 minutes, and finally allowing the mixture to stand for 10 to 30 minutes.

5. The preparation method according to claim 3, characterized in that the drying of the acid-base blend membrane is vacuum drying at 30-40 ℃ for 2-3h, and then vacuum drying at 80-100 ℃ for 12-15h.

6. The use of the acid-base blend membrane for proton exchange membrane fuel cell as claimed in claim 1 as a proton exchange membrane for fuel cell.