Functionalized graphene/Nafion composite proton exchange membrane and preparation method and application thereof
Technical Field
The invention relates to a fuel cell proton exchange membrane and a preparation method thereof, in particular to a functionalized graphene/Nafion composite proton exchange membrane and a preparation method and application thereof.
Background
Proton Exchange Membrane Fuel Cells (PEMFC) are a clean and efficient green and environment-friendly power supply, have the characteristics of high efficiency, zero pollution and the like, and are widely concerned all over the world. The Proton Exchange Membrane (PEM) is the core component of the PEMFC, and its proton conductivity directly determines the cell performance. Nafion is used as the most advanced proton exchange membrane, is a perfluorosulfonic acid polymer proton exchange membrane, has the advantages of high conductivity, good electrochemical and chemical stability, low gas permeability and the like, and is widely used for proton exchange membrane fuel cells. However, the proton conductivity of the Nafion membrane is very dependent on water and temperature, and proton transmission channels can be collapsed and collapsed under anhydrous or low-humidity conditions and high temperature, so that the proton conductivity is obviously reduced. In addition, when the Nafion membrane is used in a Direct Methanol Fuel Cell (DMFC), fuel methanol permeates seriously, and methanol molecules easily pass through an ion cluster network along with water molecules and penetrate to a cathode, so that not only is fuel wasted, but also normal reaction of the cathode is interfered, and the efficiency of the DMFC is obviously reduced. Therefore, the development of a high proton conductivity, low fuel permeability PEM is critical for large-scale applications of PEMFCs. Studies have shown that the incorporation of inorganic fillers into the Nafion membrane matrix can help in proton conduction by adjusting the microphase separation structure in the membrane matrix.
Graphene is a two-dimensional material composed of sp2 hybridized and connected carbon atom layers, and the special structure of the single atom layer makes the graphene have many unique physicochemical properties, such as high modulus, high strength, high-speed electron mobility at room temperature, high specific surface area, high thermal conductivity and the like. The excellent performances enable the graphene to have bright application prospects in the fields of nano electronic devices, sensors, energy storage, composite materials and the like. Graphene is hydrophobic and is difficult to disperse in water and common organic solvents. Therefore, in order to fully exert the excellent properties of graphene and improve the dispersibility of graphene in a Nafion matrix, it is necessary to functionally modify graphene. J.Phys.chem.C,120(2016),15855-15866, Sulfonated Graphene-Nafion Composite Membranes for polymer electrolyte Membranes Operating under reduced proton exchange membrane, which is prepared by sulfonating and modifying Graphene, introducing sulfonic acid groups on the surface of the Graphene and compounding the sulfonic acid groups with Nafion to prepare a Sulfonated Graphene/Nafion Composite proton exchange membrane, wherein the proton conductivity of the Nafion membrane under a low-Humidity condition is obviously improved, but the quantity of the sulfonic acid groups introduced on the surface of the Graphene is limited.
So far, no research is made on the preparation of a composite proton exchange membrane by introducing an acid group to the surface of graphene through diazonium salt addition reaction and atom transfer radical polymerization reaction and compounding with Nafion.
Disclosure of Invention
The invention provides a functionalized graphene/Nafion composite proton exchange membrane and a preparation method and application thereof to solve the defects.
The purpose of the invention is realized by the following technical scheme: a functionalized graphene/Nafion composite proton exchange membrane is prepared by the following preparation method, wherein the preparation method comprises the following steps:
(1) reducing graphene oxide to obtain graphene, grafting an Atom Transfer Radical Polymerization (ATRP) initiator to the surface of the graphene through a diazonium salt addition reaction to obtain ATRP initiator graft modified graphene;
(2) carrying out graft polymerization on a monomer containing an acidic group to the ATRP initiator graft-modified graphene obtained in the step (1) through ATRP reaction to obtain polymer graft graphene containing the acidic group, namely functionalized graphene;
(3) and preparing the functionalized graphene/Nafion composite proton exchange membrane by adopting a solution casting method.
The method comprises the following specific steps:
the preparation method of the ATRP initiator graft modified graphene in the step (1) comprises the following steps: firstly, Graphene Oxide (GO) prepared by a Hummers method is ultrasonically dispersed into deionized water, ascorbic acid is added to reduce the GO to obtain Graphene, then the Graphene is dispersed into the deionized water containing a surfactant, 4-aminophenylethanol and isoamyl nitrite are added, the reaction is carried out overnight at 80 ℃, the filtration, the washing and the vacuum drying are carried out to obtain hydroxyl modified Graphene (Graphene-OH), the Graphene-OH is ultrasonically dispersed into tetrahydrofuran, triethylamine is added, the alpha-bromoisobutyryl bromide is slowly dripped in the nitrogen atmosphere after the cooling to 0 ℃, the reaction is continuously carried out for 24 hours at room temperature after the dripping is finished, and finally, the filtration, the washing and the vacuum drying are carried out to obtain the ATRP initiator grafted modified Graphene (Graphene-Br).
The method for graft polymerization of the monomer containing the acidic group on the surface of the graphene by the ATRP reaction in the step (2) comprises the following steps: ultrasonically dispersing Graphene-Br obtained in the step (1) into a mixed solvent of deionized water and methanol, adding a monomer containing an acidic group, performing freeze-thaw degassing cycle for three times, adding a catalyst in a nitrogen atmosphere, reacting for 48 hours at room temperature, filtering, washing, and performing vacuum drying to obtain functionalized Graphene, namely the polymer grafted Graphene containing the acidic group.
The acid group-containing monomer used in the step (2) is 3-sulfopropyl methacrylate potassium Salt (SPMA) or 4-styrene sulfonic acid sodium salt (NASS); the catalyst is 2,2' -bipyridine/cuprous bromide; the prepared functionalized graphene, namely the polymer grafted graphene containing the acidic group, has the following structure:
the method for preparing the functionalized graphene/Nafion composite proton exchange membrane in the step (3) comprises the following steps: firstly, dispersing the functionalized graphene prepared in the step (2) into N, N-Dimethylformamide (DMF), mixing the N, N-dimethylformamide with a DMF solution of Nafion, obtaining a uniform membrane casting solution under the alternate action of ultrasound and stirring, casting to form a membrane, drying in vacuum, and finally treating with hydrogen peroxide, deionized water and a sulfuric acid solution in sequence to obtain the functionalized graphene/Nafion composite proton exchange membrane.
In the step (3), the mass ratio of the Nafion to the functionalized graphene is 100: 0.5-2.
The functionalized graphene/Nafion composite proton exchange membrane can be used for a methanol fuel cell.
The invention has the following beneficial effects:
1. according to the invention, a polymer containing an acid group is grafted on the surface of graphene through diazonium salt addition and Atom Transfer Radical Polymerization (ATRP), and is compounded with Nafion to prepare the functionalized graphene/Nafion composite proton exchange membrane, the acid group on the surface of the functionalized graphene and the acid group in a Nafion matrix can form a high-efficiency continuous proton transfer channel at an organic-inorganic interface, meanwhile, the water retention performance of the Nafion membrane can be improved, the water environment of the membrane proton transfer channel is optimized, and thus the proton conduction reinforcement under the conditions of high temperature and low humidity is realized.
2. The polymer grafted graphene containing the acid groups prepared by the method can improve the dispersibility of the graphene in a Nafion matrix, and the two-dimensional layered structure of the graphene can effectively regulate and control the channel size, prevent the diffusion of methanol molecules and realize the reinforcement of the alcohol resistance of a Nafion membrane.
3. The functionalized graphene/Nafion composite proton exchange membrane prepared by the invention can solve the common key scientific problems of rapid attenuation of proton conductivity and high methanol fuel permeability of the Nafion proton exchange membrane under high-temperature and low-humidity conditions, and can enable the Nafion membrane to have wider prospects in the aspect of commercial application and popularization of proton exchange membrane fuel cells.
Drawings
FIG. 1 is an FTIR spectrum of Graphene oxide (a), Graphene (b), hydroxyl-modified Graphene (Graphene-OH) (c), ATRP initiator graft-modified Graphene (Graphene-Br) (d) and polymer graft Graphene (e) containing acidic groups prepared according to the present invention;
FIG. 2a is an SEM image of a pure Nafion membrane;
fig. 2b is an SEM image of the functionalized graphene/Nafion composite proton exchange membrane prepared by the present invention.
Detailed Description
The present invention will be further described with reference to the following examples, but the present invention is not limited thereto.
Example 1
Dispersing 0.5g of Graphene Oxide (GO) prepared by a Hummers method into 250mL of deionized water by ultrasonic for 30 minutes, adding 10g of ascorbic acid, heating to 60 ℃, stirring for 4 hours, cooling to room temperature, filtering, washing with deionized water for three times, adding 0.5g of obtained product and sodium dodecyl sulfate into 250mL of deionized water, performing ultrasonic for 30 minutes, adding 2g of 4-aminophenylethanol and 1.5mL of isoamyl nitrite, reacting at 80 ℃ overnight, cooling to room temperature, filtering, washing with deionized water, absolute ethanol and acetone in sequence, and performing vacuum drying to obtain hydroxyl modified Graphene (Graphene-OH). Adding 0.2g of Graphene-OH into 40mL of tetrahydrofuran, adding 2mL of triethylamine, introducing nitrogen for 10 minutes, cooling to 0 ℃, slowly dropwise adding a solution of 1.2mL of alpha-bromoisobutyryl bromide/10 mL of tetrahydrofuran, continuing to react for 24 hours at room temperature after dropwise adding is finished, finally filtering, washing by sequentially adopting deionized water, absolute ethyl alcohol and acetone, drying in vacuum, and drying in vacuum to obtain the ATRP initiator graft modified Graphene (Graphene-Br).
Dispersing 0.1g of Graphene-Br into 20mL of methanol/deionized water mixed solvent (the mass ratio is 3:2) by ultrasonic dispersion, adding 3.2g of 3-sulfopropyl methacrylate potassium Salt (SPMA), performing freeze-thaw degassing cycle for three times, adding 0.0625g of 2,2' -bipyridine and 0.0287g of cuprous bromide under the nitrogen atmosphere, reacting at room temperature for 48 hours, filtering, washing with deionized water for three times, immersing the product into 1M sulfuric acid solution, standing overnight, washing with deionized water to be neutral, and performing freeze drying to obtain the acid group-containing polymer grafted Graphene.
Dispersing 2.5mg of acid group-containing polymer grafted graphene into 2mL of N, N-Dimethylformamide (DMF) by ultrasonic treatment for 4h, dissolving 0.5g of Nafion into 8mL of DMF, mixing the two solutions, performing ultrasonic treatment for 30 min and stirring for 30 min, circulating for four times to obtain a uniform membrane casting solution, casting to form a membrane, performing vacuum drying at 80 ℃ for 12 h, heating to 120 ℃ and drying for 12 h, and finally sequentially performing treatment with hydrogen peroxide (3%), deionized water and sulfuric acid solution (1M) at 80 ℃ to obtain the 0.5 wt% functionalized graphene/Nafion composite proton exchange membrane.
Example 2
Dispersing Graphene Oxide (GO) prepared by a Hummers method for 0.5 ultrasonic 30 minutes into 250mL of deionized water, adding 10g of ascorbic acid, heating to 60 ℃, stirring for 4 hours, cooling to room temperature, filtering, washing with deionized water for three times, adding the obtained product and 0.5g of sodium dodecyl sulfate into 250mL of deionized water, performing ultrasonic 30 minutes, adding 2g of 4-aminophenylethanol and 1.5mL of isoamyl nitrite, reacting overnight at 80 ℃, cooling to room temperature, filtering, washing with deionized water, absolute ethanol and acetone in sequence, and performing vacuum drying to obtain hydroxyl modified Graphene (Graphene-OH). Adding 0.2g of Graphene-OH into 40mL of tetrahydrofuran, adding 2mL of triethylamine, introducing nitrogen for 10 minutes, cooling to 0 ℃, slowly dropwise adding a solution of 1.2mL of alpha-bromoisobutyryl bromide/10 mL of tetrahydrofuran, continuing to react for 24 hours at room temperature after dropwise adding is finished, finally filtering, washing by sequentially adopting deionized water, absolute ethyl alcohol and acetone, drying in vacuum, and drying in vacuum to obtain the ATRP initiator graft modified Graphene (Graphene-Br).
Dispersing 0.1g of Graphene-Br into 20mL of methanol/deionized water mixed solvent (the mass ratio is 3:2) by ultrasonic dispersion, adding 3.2g of 3-sulfopropyl methacrylate potassium Salt (SPMA), performing freeze-thaw degassing cycle for three times, adding 0.0625g of 2,2' -bipyridine and 0.0287g of cuprous bromide under the nitrogen atmosphere, reacting at room temperature for 48 hours, filtering, washing with deionized water for three times, immersing the product into 1M sulfuric acid solution, standing overnight, washing with deionized water to be neutral, and performing freeze drying to obtain the acid group-containing polymer grafted Graphene.
Dispersing 5mg of acid group-containing polymer grafted graphene into 2mL of N, N-Dimethylformamide (DMF) by ultrasonic treatment for 4h, dissolving 0.5g of Nafion into 8mL of DMF, mixing the two solutions, performing ultrasonic treatment for 30 min and stirring for 30 min, circulating for four times to obtain a uniform membrane casting solution, casting to form a membrane, performing vacuum drying at 80 ℃ for 12 h, heating to 120 ℃ and drying for 12 h, and finally sequentially performing treatment with hydrogen peroxide (3%), deionized water and sulfuric acid solution (1M) at 80 ℃ to obtain the 1 wt% functionalized graphene/Nafion composite proton exchange membrane.
Example 3
Dispersing Graphene Oxide (GO) prepared by a Hummers method for 0.5 ultrasonic 30 minutes into 250mL of deionized water, adding 10g of ascorbic acid, heating to 60 ℃, stirring for 4 hours, cooling to room temperature, filtering, washing with deionized water for three times, adding the obtained product and 0.5g of sodium dodecyl sulfate into 250mL of deionized water, performing ultrasonic 30 minutes, adding 2g of 4-aminophenylethanol and 1.5mL of isoamyl nitrite, reacting overnight at 80 ℃, cooling to room temperature, filtering, washing with deionized water, absolute ethanol and acetone in sequence, and performing vacuum drying to obtain hydroxyl modified Graphene (Graphene-OH). Adding 0.2g of Graphene-OH into 40mL of tetrahydrofuran, adding 2mL of triethylamine, introducing nitrogen for 10 minutes, cooling to 0 ℃, slowly dropwise adding a solution of 1.2mL of alpha-bromoisobutyryl bromide/10 mL of tetrahydrofuran, continuing to react for 24 hours at room temperature after dropwise adding is finished, finally filtering, washing by sequentially adopting deionized water, absolute ethyl alcohol and acetone, drying in vacuum, and drying in vacuum to obtain the ATRP initiator graft modified Graphene (Graphene-Br).
Dispersing 0.1g of Graphene-Br into 20mL of methanol/deionized water mixed solvent (the mass ratio is 3:2) by ultrasonic dispersion, adding 3.2g of 3-sulfopropyl methacrylate potassium Salt (SPMA), performing freeze-thaw degassing cycle for three times, adding 0.0625g of 2,2' -bipyridine and 0.0287g of cuprous bromide under the nitrogen atmosphere, reacting at room temperature for 48 hours, filtering, washing with deionized water for three times, immersing the product into 1M sulfuric acid solution, standing overnight, washing with deionized water to be neutral, and performing freeze drying to obtain the acid group-containing polymer grafted Graphene.
Dispersing 7.5mg of acid group-containing polymer grafted graphene into 2mL of N, N-Dimethylformamide (DMF) by ultrasonic treatment for 4h, dissolving 0.5g of Nafion into 8mL of DMF, mixing the two solutions, performing ultrasonic treatment for 30 min and stirring for 30 min, circulating for four times to obtain a uniform membrane casting solution, casting to form a membrane, performing vacuum drying at 80 ℃ for 12 h, heating to 120 ℃ and drying for 12 h, and finally sequentially performing treatment with hydrogen peroxide (3%), deionized water and sulfuric acid solution (1M) at 80 ℃ to obtain the 1.5 wt% functionalized graphene/Nafion composite proton exchange membrane.
Example 4
Dispersing Graphene Oxide (GO) prepared by a Hummers method for 0.5 ultrasonic 30 minutes into 250mL of deionized water, adding 10g of ascorbic acid, heating to 60 ℃, stirring for 4 hours, cooling to room temperature, filtering, washing with deionized water for three times, adding the obtained product and 0.5g of sodium dodecyl sulfate into 250mL of deionized water, performing ultrasonic 30 minutes, adding 2g of 4-aminophenylethanol and 1.5mL of isoamyl nitrite, reacting overnight at 80 ℃, cooling to room temperature, filtering, washing with deionized water, absolute ethanol and acetone in sequence, and performing vacuum drying to obtain hydroxyl modified Graphene (Graphene-OH). Adding 0.2g of Graphene-OH into 40mL of tetrahydrofuran, adding 2mL of triethylamine, introducing nitrogen for 10 minutes, cooling to 0 ℃, slowly dropwise adding a solution of 1.2mL of alpha-bromoisobutyryl bromide/10 mL of tetrahydrofuran, continuing to react for 24 hours at room temperature after dropwise adding is finished, finally filtering, washing by sequentially adopting deionized water, absolute ethyl alcohol and acetone, drying in vacuum, and drying in vacuum to obtain the ATRP initiator graft modified Graphene (Graphene-Br).
Dispersing 0.1g of Graphene-Br into 20mL of methanol/deionized water mixed solvent (the mass ratio is 3:2) by ultrasonic dispersion, adding 3.2g of 3-sulfopropyl methacrylate potassium Salt (SPMA), performing freeze-thaw degassing cycle for three times, adding 0.0625g of 2,2' -bipyridine and 0.0287g of cuprous bromide under the nitrogen atmosphere, reacting at room temperature for 48 hours, filtering, washing with deionized water for three times, immersing the product into 1M sulfuric acid solution, standing overnight, washing with deionized water to be neutral, and performing freeze drying to obtain the acid group-containing polymer grafted Graphene.
Dispersing 10mg of acid group-containing polymer grafted graphene into 2mL of N, N-Dimethylformamide (DMF) by ultrasonic for 4h, dissolving 0.5g of Nafion into 8mL of DMF, mixing the two solutions, performing ultrasonic treatment for 30 min and stirring for 30 min, circulating for four times to obtain a uniform membrane casting solution, casting to form a membrane, performing vacuum drying at 80 ℃ for 12 h, heating to 120 ℃ and drying for 12 h, and finally sequentially performing treatment with hydrogen peroxide (3%), deionized water and sulfuric acid solution (1M) at 80 ℃ to obtain the 2 wt% functionalized graphene/Nafion composite proton exchange membrane.
As shown in fig. 1, FTIR spectra of Graphene oxide (a), Graphene (b), hydroxyl-modified Graphene (Graphene-OH) (c), ATRP initiator graft-modified Graphene (Graphene-Br) (d), and polymer graft Graphene (e) containing acidic groups obtained in the preparation process of the present invention.
Fig. 2a is an SEM image of a pure Nafion membrane, and fig. 2b is an SEM image of a functionalized graphene/Nafion composite proton exchange membrane prepared by the present invention. The performance of the functionalized graphene/Nafion composite proton exchange membrane prepared by the invention is compared with that of a pure Nafion membrane, and the result is shown in Table 1:
TABLE 1 comparison of the Performance of the functionalized graphene/Nafion composite proton exchange membranes with that of the pure Nafion membranes
As can be seen from table 1, the functionalized graphene/Nafion composite proton exchange membrane provided by the invention is obviously superior to a pure Nafion membrane in each performance index.