CN108285643A - Cellulose nano-fibrous/the Sulfonated Polyethersulfone Proton Exchange Membrane of one kind and preparation method - Google Patents

Abstract

The invention provides a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and its preparation method. The proton exchange membrane material of the invention uses sulfonated polyethersulfone as a matrix material and is prepared by electrostatically assisted solution jet spinning Cellulose nanofibers, cellulose nanofibers are embedded in a matrix material to prepare a composite film. In order to overcome the disadvantages of high swelling rate and poor stability of sulfonated non-fluorinated hydrocarbon polymers due to excessive sulfonation, the introduction of cellulose nanofibers improves the proton conductivity of sulfonated polyethersulfone membrane materials and ensures The composite membrane has a certain mechanical strength and good alcohol resistance performance. The introduction of hydroxyl as a hydrophilic group further improves the hydrophilic performance. The existence of a large number of sulfonic acid groups also ensures the proton transport capacity of the proton exchange membrane. The proton conductivity of the proton exchange membrane of the present invention is 0.06-0.13 S/cm at 80° C., and the thickness of the proton exchange membrane is 85-120 μm.

Description

A kind of cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and its preparation method

technical field

The invention relates to the technical field of proton exchange membranes, in particular to a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and a preparation method.

Background technique

Fuel cell (Fuel cell) is an efficient and clean energy utilization method, which can directly convert the chemical energy stored in fuel and oxidant into electrical energy, with a high energy conversion rate, and has the advantages of high efficiency, convenience, and environmental protection. Direct Methanol Fuel Cell (DMFC) uses methanol as fuel. It has the characteristics of low-temperature fast start-up, clean and environmentally friendly fuel, and simple battery structure. It is widely used in all aspects of life.

Proton Exchange Membrane (PEM) is one of the core components of direct methanol fuel cells, which plays a role in conducting protons and isolating fuel and electrons. Its performance directly affects the performance of fuel cells. The currently widely used perfluorosulfonic acid membrane represented by Nafion membrane has problems such as complex preparation process, high cost, and decreased performance at high temperature. Proton conductivity is one of the most important parameters to measure the performance of proton exchange membranes, and improving proton conductivity is an effective means to obtain high-performance proton exchange membrane fuel cells. In recent years, nanofiber-modified proton exchange membranes have provided new research ideas for improving the proton conductivity and other properties of proton exchange membranes. The use of proton-conducting nanofibers can realize the enrichment of proton carriers along the radial direction of the nanofibers, which is conducive to the formation of long-range ordered proton transfer channels, or add hydrophilic substances to improve the water retention of the composite membrane, thereby improving the proton conduction of the membrane. performance.

Due to the limitations of electrospun nanofibers in the membrane structure, the electrospun nanofiber composite membrane prepared by solution impregnation method is likely to cause incomplete filling of the film-forming matrix in the fiber gap, and the surface on both sides of the composite membrane is inevitably formed without The "transfer barrier layer" of nanofibers and weak proton conductivity, thus affecting the proton conductivity of the proton exchange membrane.

Contents of the invention

In view of the above shortcomings, the object of the present invention is to provide a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and a preparation method.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and a preparation method thereof, comprising the following steps:

S1 uses cellulose acetate as a raw material, and prepares cellulose acetate nanofibers by solution jet spinning, and the fiber diameter distribution is about 50-1100nm;

S2 is hydrolyzed in sodium hydroxide alcoholic solution to obtain cellulose nanofibers;

S3 dissolving the sulfonated polyethersulfone particles in the solvent N, N-dimethylformamide (DMF) to prepare a sulfonated polyethersulfone solution with a molecular weight of 30000-60000 and a sulfonation degree of 60-80%;

S4 immersing the cellulose nanofibers into a sulfonated polyethersulfone solution by a solution impregnation method to prepare a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane.

Preferably, the solvents are uniformly mixed at a volume ratio of 2:1 to prepare a spinning solution with a mass fraction of cellulose acetate of 10-18%.

Preferably, the reaction solvent is two of acetone, N,N-dimethylformamide, N,N-dimethylacetamide, water, and chloroform, or a mixed solvent of several of them.

Preferably, the concentration of the sodium hydroxide alcohol solution is 0.05-0.1 mol/L.

Preferably, the mass fraction of sulfonated polyethersulfone in the sulfonated polyethersulfone solution is 10-20%.

Preferably, the quality of cellulose nanofibers is 1% to 30% of that of cellulose nanofibers/sulfonated polyethersulfone proton exchange membrane. Preferably, the quality of cellulose nanofibers in step S4 is cellulose nanofibers/ 2-20% of sulfonated polyethersulfone proton exchange membrane.

Preferably, the thickness of the proton exchange membrane is 85-120 μm.

The invention provides sulfonated polyether sulfone polymer as raw material, adopts solution jet spinning method to prepare cellulose acetate nanofiber, carries out hydrolysis reaction in sodium hydroxide alcoholic solution, obtains cellulose nanofiber; sulfonated polyether The sulfone particles are dissolved in the solvent N, N-dimethylformamide (DMF) to prepare a sulfonated polyethersulfone solution; the cellulose nanofibers are immersed in the sulfonated polyethersulfone solution by solution impregnation to prepare cellulose Nanofiber/sulfonated polyethersulfone proton exchange membrane. The invention utilizes a solution impregnation method to uniformly disperse the cellulose nanofibers in the sulfonated polyethersulfone solution to form a dense and non-porous composite membrane, adding cellulose nanofibers with obvious three-dimensional curling characteristics to form an obvious transmembrane structure , the proton carriers are enriched along the radial direction of the nanofibers, which is conducive to the formation of long-range ordered proton transfer channels, and the addition of hydrophilic cellulose nanofibers improves the water retention of the composite membrane, thereby improving the proton conductivity of the membrane. Moreover, the invention adds three-dimensional crimped nanofibers to form an effective alcohol barrier layer and reduce the methanol permeability of the proton exchange membrane.

The present invention provides a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane prepared by the preparation method described in the scheme above, which has good proton conductivity and alcohol resistance. Experimental results show that the proton conductivity of the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane provided by the invention can reach 0.13 S/cm, and the methanol permeability is as low as 4.45×10 ^{- 7} cm ² /s.

Description of drawings

Fig. 1 is the electron microscope observation figure of the obtained proton exchange membrane section of the embodiment of the present invention 1;

Fig. 2 is the electron microscope observation figure of the obtained proton exchange membrane section of embodiment 2 of the present invention;

Fig. 3 is the electron microscope observation figure of the obtained proton exchange membrane section of embodiment 3 of the present invention;

Fig. 4 is the electron microscope observation figure of the obtained proton exchange membrane section of the embodiment of the present invention 4;

Fig. 5 is the electron microscope observation figure of the obtained proton exchange membrane section of embodiment 5 of the present invention;

Fig. 6 is a test chart of the proton conductivity of the proton exchange membrane obtained in the example of the present invention.

Detailed ways

A cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and a preparation method thereof, characterized in that it comprises the following steps:

S1 uses cellulose acetate as a raw material, and prepares cellulose acetate nanofibers by solution jet spinning, and the fiber diameter distribution is about 50-1100nm;

S2 is hydrolyzed in sodium hydroxide alcoholic solution to obtain cellulose nanofibers;

S3 dissolving the sulfonated polyethersulfone particles in the solvent N,N-dimethylformamide (DMF) to prepare a casting solution with a molecular weight of 30000-60000 and a sulfonation degree of 60-80%;

S4 immersing the cellulose nanofibers into a sulfonated polyethersulfone solution by a solution impregnation method to prepare a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane.

The invention uses cellulose acetate as a raw material and adopts a solution jet spinning method to prepare cellulose acetate nanofibers. In the present invention, the cellulose acetate is preferably a polymer with Mn=30000～50000, DS=2.45, and the polymer is preferably Mn=30000, DS=2.45.

The present invention preferably prepares the cellulose acetate polymer into a spinning solution, and then uses solution jet spinning for spinning; the spinning solvent for the cellulose acetate polymer is preferably acetone, N,N-dimethylformamide , N,N-dimethylacetamide, chloroform, two kinds in water, or a mixed solvent of several kinds thereof, the mass concentration of cellulose acetate in the spinning solution is 1-25%, preferably 2-5% .

In the present invention, the preparation of cellulose nanofibers by the solution jet spinning method preferably includes the following steps:

mixing the cellulose acetate polymer and the spinning solvent to obtain a spinning solution;

Jet spinning the spinning solution to obtain cellulose acetate nanofibers.

In the present invention, the feeding speed of the jet spinning is 5-25ml/h, more preferably 10-20ml/h, most preferably 20ml/h; the drafting air pressure of the solution jet spinning is 0.05- 0.2 MPa; the temperature of the spinning box in the jet spinning is preferably 20-30°C; the receiving distance from the receiving curtain to the spinneret hole in the jet spinning is preferably 40-80 cm, preferably 40-60 cm.

In some specific embodiments of the present invention, using a solution jet spinning device to carry out jet spinning preferably includes the following steps: using a syringe pump to feed the spinning solution into the spinneret liquid reservoir through a metering pump, and the spinning solution is fed from the jet Extrude from the filament head to form a thin stream of spinning solution, which is drawn and thinned by the drafting airflow and then enters the spinning box to form fibers. The fibers are collected and condensed on the receiving net curtain by a fan to obtain Proton-conducting nanofiber mat; under the joint action of drafting airflow and spinning box heating, the solvent in the fine stream of spinning solution evaporates to form fibers.

In the present invention, the cellulose acetate polymer is preferably formulated into a spinning solution, which is spun by solution jet spinning, and hydrolyzed in a sodium hydroxide alcoholic solution to obtain cellulose nanofibers. The thickness of the cellulose nanofiber is preferably 20-50 μm, preferably 30-40 μm; the diameter of the cellulose acetate nanofiber is preferably 50-1100 nm, preferably 100-800 nm, and the diameter of the cellulose nanofiber is preferably 50 nm. ~800nm, preferably 200~500nm, most preferably 200~300nm. In the present invention, the cellulose nanofibers form an effective alcohol barrier layer, reducing the methanol permeability of the proton exchange membrane.

In the present invention, the sulfonated polyethersulfone particles are dissolved in the solvent N,N-dimethylformamide (DMF) to prepare the sulfonated polyethersulfone solution, and the preferred mass concentration of the sulfonated polyethersulfone is 10-30%, more preferably Preferably it is 10 to 20%.

After obtaining the cellulose nanofiber and the sulfonated polyethersulfone solution, the present invention immerses the cellulose nanofiber into the sulfonated polyethersulfone solution by means of solution impregnation to prepare the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane. The mass of the cellulose nanofiber is 1-25% of the mass of the proton exchange membrane, preferably 2-5%.

After immersing the cellulose nanofibers in the sulfonated polyethersulfone solution, the present invention soaks the composite membrane in water for 12 hours, removes the solvent in the composite membrane, and then puts it into a freeze dryer for freeze-drying, and the freezing time is 12 hours ; The composite membrane is hot pressed to obtain the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane. In the present invention, the temperature of the hot pressing is preferably 100-200°C, preferably 120-150°C; the pressure of the pressure is preferably 5-15MPa, preferably 6-10MPa; the hot-pressing time is preferably 5-15s, preferably 6-10s; the present invention preferably uses a flat-plate hot press for hot pressing.

The present invention provides a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane prepared by the preparation method described in the scheme above. In the present invention, the thickness of the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane is preferably 85-120 μm, preferably 90-110 μm.

The cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane and the preparation method provided by the present invention will be described in detail below in conjunction with the examples, but they should not be construed as limiting the protection scope of the present invention.

Example 1

With acetone and N, N-dimethylacetamide (DMAc) as spinning solvent, cellulose acetate was dissolved in the spinning solution to prepare a solution with a mass concentration of cellulose acetate of 17%; The spinning solution is fed into the spinneret liquid reservoir through the metering pump at a speed of /h. When the spinning solution is extruded from the spinneret, a thin stream is formed, and the thin stream passes through the high-pressure drafting airflow (pressure is 0.05MPa). After drafting and refining, it enters the spinning box (box temperature is 25°C), under the joint action of high-pressure airflow and spinning box, the solvent volatilizes to form fibers, and the fibers are collected on the receiving net curtain by the fan (the receiving distance is 40cm), obtain cellulose acetate nanofibers, control the thickness of cellulose acetate nanofibers to be 40 μm;

The sulfonated polyethersulfone microspheres were dissolved in N,N-dimethylformamide (DMF) to prepare a solution with a mass concentration of sulfonated polyethersulfone of 15%.

Put the cellulose acetate nanofiber into the prepared 0.05mol/L sodium hydroxide solution for hydrolysis, and the hydrolysis time is 24h. After the hydrolysis is completed, wash with distilled water, remove excess sodium hydroxide solution, and dry at 60° C. for 10 h.

Then adopt the method of solution impregnation, immerse the cellulose nanofibers in the sulfonated polyethersulfone solution, make the quality of the cellulose nanofibers be 2% of the mass of the proton exchange membrane, the cellulose nanofibers can be obtained by casting and scraping membrane method /Sulfonated polyethersulfone proton exchange membrane (SPES/Cell-2) with a thickness of 100 μm.

The proton exchange membrane was brittle, and the cross-section of the proton exchange membrane was observed with a scanning electron microscope. The observation results are shown in Figure 1. According to Figure 1, it can be seen that the inside of the membrane is fully filled, and the nanofibers are distributed in the matrix.

Example 2

Only the quality of the cellulose nanofibers was improved during the impregnation process, and other conditions were completely the same as in Example 1 to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane.

The mass of the cellulose nanofibers is 3% of the mass of the proton exchange membrane to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane (SPES/Cell-3) with a thickness of 104 μm.

The proton exchange membrane was brittle, and the cross-section of the proton exchange membrane was observed with a scanning electron microscope. The observation results are shown in FIG.

Example 3

Only the quality of the cellulose nanofibers was improved during the impregnation process, and other conditions were completely the same as in Example 1 to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane.

The mass of the cellulose nanofibers is 4% of the mass of the proton exchange membrane to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane (SPES/Cell-4) with a thickness of 110 μm.

The proton exchange membrane was brittle, and the cross-section of the proton exchange membrane was observed with a scanning electron microscope. The observation results are shown in FIG. 3 . It can be seen from FIG. 3 that the observation results are similar to those in Example 1.

Example 4

Only the quality of the cellulose nanofibers was improved during the impregnation process, and other conditions were completely the same as in Example 1 to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane.

The mass of the cellulose nanofibers is 5% of the mass of the proton exchange membrane to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane (SPES/Cell-5) with a thickness of 112 μm.

The proton exchange membrane was brittle, and the cross-section of the proton exchange membrane was observed with a scanning electron microscope. The observation results are shown in FIG. 4 . It can be seen from FIG.

Example 5

Only the quality of the cellulose nanofibers was improved during the impregnation process, and other conditions were completely the same as in Example 1 to obtain a cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane.

The mass of the cellulose nanofiber is 20% of the mass of the proton exchange membrane to obtain the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane with a thickness of 90 μm.

The proton exchange membrane was brittle, and the cross-section of the proton exchange membrane was observed with a scanning electron microscope. The observation results are shown in FIG. 5 . It can be seen from FIG. 5 that the observation results are similar to those in Example 1.

Comparative example 1

The sulfonated polyethersulfone microspheres were dissolved in N,N-dimethylformamide (DMF) to prepare a solution with a mass concentration of sulfonated polyethersulfone of 15%. The pure SPES film was prepared by casting scrape film method with a thickness of 100 μm.

Example 6

The nanofiber/sulfonated polyethersulfone proton exchange membrane and the pure SPES membrane obtained in Examples 1-5 and Comparative Example 1 were tested for performance, and the obtained data are listed in Table 1;

Proton conductivity: use the CH1660D electrochemical workstation to measure the resistance of the sample film and its two electrodes (detection temperature 80 ° C, humidity 100%), and then calculate the proton conductivity by formula 1:

In formula 1, σ: represents the proton conductivity, the unit is (S/cm); l represents the distance between the two electrodes, the unit is cm; t represents the thickness of the sample film, the unit is cm; w represents the width of the sample film, The unit is cm, R represents the resistance of the sample film, and the unit is Ω.

Methanol transmission rate: the methanol transmission rate of the proton exchange membrane is detected by gas chromatography, and the methanol diffusion coefficient is calculated according to Ficker's first law, as follows:

Among them, DK (cm ² s ^-1 ) is the permeability coefficient of methanol; C _A (mol/L) and C _B (mol/L) are the concentration of methanol in the two pools A and B respectively; A (cm ² ) is the membrane The cross-sectional area; L is the thickness (cm), V _B is the diffusion volume (L).

The test result of table 1 embodiment 1～5 and SPES

According to Table 1, it can be seen that the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane provided by the present invention is compared with the pure SPES membrane, and the proton conductivity is improved, and the methanol permeability is improved, indicating that the cellulose provided by the present invention The existence of nanofibers can realize the enrichment of proton carriers along the radial direction of nanofibers, which is conducive to the formation of long-range ordered proton transfer channels. The addition of hydrophilic cellulose nanofibers improves the water retention of the composite membrane and improves the membrane stability. Proton conduction performance, so as to realize the high-efficiency transfer of protons; the performance of the cellulose nanofiber/sulfonated polyethersulfone proton exchange membrane obtained in the present invention is obviously better than that of the SPES membrane.

The above is only a preferred embodiment of the present invention, and it should be pointed out that for those of ordinary skill in the art, some improvements and modifications can be made without departing from the principle of the present invention. It should be regarded as the protection scope of the present invention.

Claims (8)

1. a kind of cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane and preparation method, which is characterized in that including following step Suddenly：

S1 prepares cellulose acetate nanofiber, fibre diameter point using cellulose acetate as raw material, using solution jet spinning method Cloth is between 50~1100nm；

Reaction is hydrolyzed in S2 in sodium hydroxide alcoholic solution, obtains cellulose nano-fibrous；

S3 sulfonated polyether sulfone grain dissolution is prepared in solvent n,N-Dimethylformamide (DMF) molecular weight be 30000~ 60000, the sulfonated polyether sulfolane solution that sulfonation degree is 60~80%；

The cellulose nano-fibrous method using solution dipping is immersed in sulfonated polyether sulfolane solution and prepares cellulose by S4 Nanofiber/Sulfonated Polyethersulfone Proton Exchange Membrane.

2. one kind according to claim 1 is cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane and preparation method, It is characterized in that, the preparation method of the cellulose acetate nanofiber in the step S1 is as follows：

Solvent is mixed with the ratio uniform of volume ratio 2: 1~5: 1, it is 10~18% to be configured to cellulose acetate mass fraction Spinning solution.

3. one kind according to claim 1 is cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane and preparation method, It is characterized in that, a concentration of 0.05~0.2mol/L of sodium hydroxide alcoholic solution in the step S2.

4. one kind according to claim 1 is cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane and preparation method, It is characterized in that, the mass fraction of sulfonated polyether sulfone is 10~30% in the step S3 sulfonated polyether sulfolane solutions.

5. one kind according to claim 1 is cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane and preparation method, It is characterized in that, the cellulose nano-fibrous quality in the step S4 is that cellulose nano-fibrous/sulfonated polyether sulfone proton is handed over Change the 2~30% of film.

6. one kind according to claim 2 is cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane and preparation method, It is characterized in that, the reaction dissolvent is acetone, n,N-Dimethylformamide, n,N-dimethylacetamide, trifluoro-ethylene, in water Two kinds or in which several mixed solvents.

7. cellulose nano-fibrous/the Sulfonated Polyethersulfone Proton Exchange Membrane of one kind according to claims 1 to 6 and preparation side Method, which is characterized in that the thickness of the cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane is 85~120 μm.

8. a kind of cellulose fibre/Sulfonated Polyethersulfone Proton Exchange Membrane according to claim 5 and preparation method, feature It is that the cellulose nano-fibrous quality in the step S4 is cellulose nano-fibrous/Sulfonated Polyethersulfone Proton Exchange Membrane 2~5%.