Disclosure of Invention
The invention aims to provide application of a dendritic nanofiber non-woven fabric in preparation of a dendritic nanofiber/Nafion composite membrane, namely the dendritic nanofiber non-woven fabric is used as a carrier, and Nafion is impregnated and compounded to prepare the composite membrane used as a proton exchange membrane of a fuel cell. The micro-branch optimization of the dendritic nano-fiber, the Nafion polymer matrix interface structure and the proton transfer channel, particularly the acid-base pair is constructed by the amino-rich polymer macromolecules of the amide dendritic nano-fiber and sulfonic acid groups in Nafion molecules, and the modified Nafion membrane with excellent proton transfer performance is cooperatively constructed.
The invention also aims to provide a preparation method for preparing the dendritic nanofiber/Nafion composite membrane.
The preparation method of the dendritic nanofiber/Nafion composite membrane is characterized by comprising the following steps:
(1) dendritic nanofiber/Nafion padding composite
Firstly, unwinding the 60-100 mu m dendritic nanofiber non-woven fabric at the speed of 1-3m/min, immersing the non-woven fabric into 5% Nafion solution, extruding and rolling the non-woven fabric by a 0.1-0.3MPa rubber roller, immersing the non-woven fabric into 10% Nafion solution, and extruding and rolling the non-woven fabric by a 0.3-0.5MPa rubber roller to obtain the dendritic nanofiber/Nafion composite membrane.
(2) Drying by baking with oven for dendritic nanofiber/Nafion composite membrane
And conveying the prepared dendritic nanofiber/Nafion composite membrane to a low-temperature drying oven at 50-70 ℃, and then conveying the composite membrane into a high-temperature drying oven at 110-130 ℃ to obtain the dry dendritic nanofiber/Nafion composite membrane.
(3) Dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry dendritic nanofiber/Nafion composite membrane to a smooth roller heat setting machine with the temperature of 50-70 ℃ and the pressure of 1-3MPa for shaping and surface leveling treatment to obtain the dendritic nanofiber/Nafion composite membrane.
The preparation method of the nano-fiber with the multi-stage structure is characterized in that tetrabutylammonium chloride in electrostatic spinning solution is used for increasing the conductivity of the spinning solution and simultaneously reducing the acting force among macromolecules, so that jet flow is split in the electrospinning process to form a nano-fiber film with the dendritic structure. The tetrabutylammonium chloride has excellent hydrophilicity, the dendritic nano-fibers have higher specific surface area, and the tetrabutylammonium chloride can have strong interface binding capacity with Nafion and construct more long-range ordered proton transmission channels, thereby being beneficial to the jump conduction of protons. The preparation method of the dendritic nanofiber adopts a known electrostatic spinning technology, can realize large-scale production, and the diameter and the distribution of the prepared fiber can be adjusted by changing the types and the process parameters of polymers. The preparation method of the composite membrane can be realized by adopting the processes of two-dipping and two-rolling, hot drying and hot setting, and the method has the advantages of simple process, high production efficiency and easy industrial implementation.
The polymer which can be used for the production of the dendritic nano-fiber has more types, such as cellulose acetate, polyvinylidene fluoride, polyurethane, polyamide-6, poly-m-phenylene isophthalamide and the like. The amide polymer contains-NH 2 group molecules, can form acid-base pairs with sulfonate in Nafion, and is a preferable dendritic nanofiber polymer raw material in the invention.
In the method for improving the proton conductivity of the Nafion membrane, step 1) in the process, a two-dipping and two-rolling process is adopted, the dendritic nano-fiber non-woven fabric is firstly subjected to padding by using a low-concentration 5% Nafion solution, and the low concentration of the target is favorable for the Nafion to diffuse into the nano-fiber non-woven fabric; padding with a high-concentration 10% Nafion solution to ensure that Nafion is sufficiently filled in pores of the dendritic nanofibers, and squeezing and rolling with a rubber roller to be relatively soft to prevent the dendritic nanofibers from being excessively compacted tightly in a wet state; and 2) adopting a hot drying oven, wherein the process aims at evaporating alcohol solvent in the Nafion solution, and simultaneously, the membrane generates certain shrinkage to densify the membrane. The drying temperature of the low-temperature hot drying oven cannot exceed 70 ℃, otherwise, the dendritic nanofiber non-woven fabric can excessively shrink, and the overall uniformity of the composite membrane is influenced; and 3) further densifying the composite film, and endowing the surface of the composite film with smoothness.
Detailed Description
The preparation method of the dendritic nanofiber/Nafion composite membrane provided by the invention is further described in detail with reference to specific embodiments.
Example 1
(1) Polyamide-6 dendritic nanofiber/Nafion padding composite
Firstly, polyamide-6 particles, formic acid and tetrabutylammonium chloride are prepared according to a certain proportion and uniformly stirred, and the dendritic polyamide-6 nanofiber non-woven fabric with the thickness of 60-100 mu m is prepared by an electrostatic spinning technology. Wherein the concentration of the polyamide-6 in formic acid solution is 14.5 wt.%, and the concentration of the added tetrabutylammonium chloride is 4 wt.%.
And then unwinding the polyamide-6 dendritic nanofiber non-woven fabric with the thickness of 60 mu m at the speed of 3m/min, immersing the polyamide-6 dendritic nanofiber non-woven fabric into 5% Nafion solution, extruding and rolling the polyamide-6 dendritic nanofiber non-woven fabric through a 0.1MPa rubber roller, immersing the polyamide-6 dendritic nanofiber non-woven fabric into 10% Nafion solution, and extruding and rolling the polyamide-6 dendritic nanofiber non-woven fabric through a 0.3MPa rubber roller to obtain the dendritic nanofiber/Nafion composite membrane.
(2) Polyamide-6 dendritic nanofiber/Nafion composite membrane drying by baking
And conveying the prepared dendritic nano-fiber/Nafion composite membrane to a low-temperature baking drying oven at 50 ℃, and then conveying the composite membrane to a high-temperature baking drying oven at 110 ℃ to obtain the dry dendritic nano-fiber/Nafion composite membrane.
(3) Polyamide-6 dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry dendritic nanofiber/Nafion composite membrane to a smooth roll heat setting machine with the temperature of 50 ℃ and the pressure of 1MPa for shaping and surface leveling treatment to obtain the dendritic nanofiber/Nafion composite membrane.
The following examples 2-5 were prepared in the same manner as in example 1, except that the thickness of the polyamide-6 dendritic nanofiber nonwoven fabric was controlled by controlling the spinning time.
Example 2
(1) Polyamide-6 dendritic nanofiber/Nafion padding composite
Unwinding the polyamide-6 dendritic nanofiber non-woven fabric with the thickness of 70 mu m at the speed of 2.5m/min, immersing the non-woven fabric into 5% Nafion solution, extruding and rolling the non-woven fabric by a rubber roller with the pressure of 0.15MPa, immersing the non-woven fabric into 10% Nafion solution, and extruding and rolling the non-woven fabric by a rubber roller with the pressure of 0.35MPa to obtain the polyamide-6 dendritic nanofiber/Nafion composite membrane.
(2) Polyamide-6 dendritic nanofiber/Nafion composite membrane drying by baking
And conveying the prepared polyamide-6 dendritic nanofiber/Nafion composite membrane to a low-temperature hot drying oven at 55 ℃, and then conveying the composite membrane to a high-temperature hot drying oven at 115 ℃ to obtain the dry polyamide-6 dendritic nanofiber/Nafion composite membrane.
(3) Polyamide-6 dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry polyamide-6 dendritic nanofiber/Nafion composite membrane to a smooth roller heat setting machine with the temperature of 55 ℃ and the pressure of 1.5MPa for shaping and surface leveling treatment to obtain the polyamide-6 dendritic nanofiber/Nafion composite membrane.
Example 3
(1) Polyamide-6 dendritic nanofiber/Nafion padding composite
Firstly, unwinding a polyamide-6 dendritic nanofiber (shown in figure 1(a)) with the thickness of 80 microns at the speed of 2m/min, immersing the nonwoven fabric into a Nafion solution with the concentration of 5%, extruding and rolling the nonwoven fabric by a rubber roller with the pressure of 0.2MPa, immersing the nonwoven fabric into a Nafion solution with the concentration of 10%, and extruding and rolling the nonwoven fabric by a rubber roller with the pressure of 0.4MPa to obtain the dendritic nanofiber/Nafion composite membrane.
(2) Polyamide-6 dendritic nanofiber/Nafion composite membrane drying by baking
The prepared polyamide-6 dendritic nanofiber/Nafion composite membrane is conveyed to a low-temperature drying oven at 60 ℃ and then enters a high-temperature drying oven at 120 ℃ to obtain the dry dendritic nanofiber/Nafion composite membrane (as shown in figure 2 (a)).
(3) Polyamide-6 dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry polyamide-6 dendritic nanofiber/Nafion composite membrane to a smooth roller heat setting machine with the temperature of 60 ℃ and the pressure of 2MPa for shaping and surface leveling treatment to obtain the polyamide-6 dendritic nanofiber/Nafion composite membrane.
Example 4
(1) Polyamide-6 dendritic nanofiber/Nafion padding composite
The polyamide-6 dendritic nanofiber non-woven fabric with the thickness of 90 mu m is unwound at the speed of 1.5m/min and immersed into a Nafion solution with the concentration of 5 percent, extruded and rolled by a rubber roller with the pressure of 0.25MPa, then immersed into a Nafion solution with the concentration of 10 percent, and extruded and rolled by a rubber roller with the pressure of 0.45MPa to obtain the polyamide-6 dendritic nanofiber/Nafion composite membrane.
(2) Polyamide-6 dendritic nanofiber/Nafion composite membrane drying by baking
And conveying the prepared polyamide-6 dendritic nanofiber/Nafion composite membrane to a low-temperature hot drying oven at 65 ℃, and then conveying the composite membrane to a high-temperature hot drying oven at 125 ℃ to obtain the dry polyamide-6 dendritic nanofiber/Nafion composite membrane.
(3) Polyamide-6 dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry polyamide-6 dendritic nanofiber/Nafion composite membrane to a smooth roller heat setting machine with the temperature of 65 ℃ and the pressure of 1-3MPa for shaping and surface leveling treatment to obtain the polyamide-6 dendritic nanofiber/Nafion composite membrane.
Example 5
(1) Polyamide-6 dendritic nanofiber/Nafion padding composite
The polyamide-6 dendritic nanofiber non-woven fabric with the thickness of 100 mu m is unwound at the speed of 1m/min and immersed into a Nafion solution with the concentration of 5 percent, extruded and rolled by a rubber roller with the pressure of 0.3MPa, then immersed into a Nafion solution with the concentration of 10 percent, and extruded and rolled by a rubber roller with the pressure of 0.5MPa to obtain the dendritic nanofiber/Nafion composite membrane.
(2) Polyamide-6 dendritic nanofiber/Nafion composite membrane drying by baking
And conveying the prepared polyamide-6 dendritic nanofiber/Nafion composite membrane to a low-temperature drying oven at 70 ℃, and then conveying the composite membrane into a high-temperature drying oven at 130 ℃ to obtain the dry polyamide-6 dendritic nanofiber/Nafion composite membrane.
(3) Polyamide-6 dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry dendritic polyamide-6 nanofiber/Nafion composite membrane to a smooth roller heat setting machine with the temperature of 70 ℃ and the pressure of 3MPa for shaping and surface leveling treatment to obtain the polyamide-6 dendritic nanofiber/Nafion composite membrane.
Example 6
(1) Meta-aramid dendritic nanofiber/Nafion padding composite
The meta-aramid dendritic nanofiber non-woven fabric is prepared by dissolving a certain amount of aramid stock solution in DMAC (dimethylacetamide), and then adding 0.1mol/L of TABC (polyamide-grafted-maleic anhydride) through an electrostatic spinning technology. Wherein the solution concentration is 58%, and the spinning voltage and the receiving distance are respectively 30kv and 17 cm.
Firstly, unwinding a non-woven fabric with the thickness of 80 mu m and immersing the non-woven fabric into a Nafion solution with the concentration of 5% at the speed of 2m/min, extruding and rolling the non-woven fabric by a rubber roller with the pressure of 0.2MPa, then immersing the non-woven fabric into a Nafion solution with the concentration of 10%, and extruding and rolling the non-woven fabric by a rubber roller with the pressure of 0.4MPa to obtain the meta-aramid dendritic nanofiber/Nafion composite membrane.
(2) Meta-aramid dendritic nanofiber/Nafion composite membrane drying by baking
And conveying the prepared meta-aramid dendritic nanofiber/Nafion composite membrane to a low-temperature drying oven at 60 ℃, and then conveying the meta-aramid dendritic nanofiber/Nafion composite membrane into a high-temperature drying oven at 120 ℃ to obtain the dry meta-aramid dendritic nanofiber/Nafion composite membrane.
(3) Meta-aramid dendritic nanofiber/Nafion composite membrane heat setting
And finally, conveying the prepared dry meta-aramid dendritic nanofiber/Nafion composite membrane to a smooth roll heat setting machine with the temperature of 60 ℃ and the pressure of 2MPa for shaping and surface leveling treatment to obtain the meta-aramid dendritic nanofiber/Nafion composite membrane (as shown in figure 3 (b)).
Comparative example 1
(1) Polyamide-6 nanofiber/Nafion padding composite
Polyamide-6 particles and formic acid were prepared at a concentration of 14.5 wt.% and uniformly stirred, and a polyamide-6 nanofiber nonwoven fabric having a thickness of 80 μm was prepared by an electrospinning technique.
Firstly, unwinding a non-woven fabric of polyamide-6 nano fibers (shown in figure 1(b)) with the thickness of 80 mu m at the speed of 2m/min, immersing the non-woven fabric into a Nafion solution with the concentration of 5%, extruding and rolling the non-woven fabric by a rubber roller with the pressure of 0.2MPa, then immersing the non-woven fabric into a Nafion solution with the concentration of 10%, and extruding and rolling the non-woven fabric by a rubber roller with the pressure of 0.4MPa to obtain the polyamide-6 nano fibers/Nafion composite membrane.
(2) Polyamide-6 nanofiber/Nafion composite membrane drying by baking
And (3) conveying the prepared polyamide-6 nanofiber/Nafion composite membrane to a low-temperature drying oven at 60 ℃, and then conveying the composite membrane to a high-temperature drying oven at 120 ℃ to obtain the dry polyamide-6 nanofiber/Nafion composite membrane.
(3) Heat setting of polyamide-6 nano fiber/Nafion composite film
And finally, conveying the prepared dry polyamide-6 nanofiber/Nafion composite membrane to a smooth roll heat setting machine with the temperature of 60 ℃ and the pressure of 2MPa for setting and surface flattening treatment to obtain the polyamide-6 nanofiber/Nafion composite membrane (as shown in figure 2 (b)).
And (3) performance testing:
as shown in fig. 1, SEM images of the polyamide-6 dendritic nanofiber membrane and the general polyamide-6 nanofiber membrane in the steps of example 3 and comparative example 1; FIG. 2 is SEM images of a polyamide-6 dendritic nanofiber/Nafion composite membrane and a common polyamide-6 nanofiber/Nafion composite membrane prepared based on the preparation methods of example 3 and comparative example 1; FIG. 3 is a SEM image of the branched nano-aramid fiber film and the composite film thereof in example 6. According to the SEM image, the polyamide-6 dendritic nanofiber membrane and the meta-aramid dendritic nanofiber membrane both have good dendritic structures, the surfaces of the corresponding dendritic nanofiber/Nafion composite membranes are flat, obvious pores or defects do not exist, and perfect compounding of the dendritic nanofibers and Nafion is achieved.
Fig. 4 is a comparison of proton conductivity of the polyamide-6 dendritic nanofiber/Nafion composite membrane, the meta-aramid dendritic nanofiber/Nafion composite membrane, the polyamide-6 nanofiber/Nafion composite membrane, and the pure Nafion membrane prepared by the preparation methods of example 3, example 6, and comparative example 1. Wherein the proton conductivity test was performed by electrochemical workstation CHI 660D. Specifically, during testing, the sample film is placed on the two copper sheets, and the sample film is kept perpendicular to and tensioned with the two copper sheets. Wherein the test parameter setting is as follows: open circuit potential, frequency range is 0.1-105Hz, and working amplitude is 0.01V. The film resistance R corresponds to a semicircular diameter corresponding to a high frequency region in the obtained alternating current impedance spectrum. The calculation formula is as follows (1):
wherein, L (cm), A (cm)2) And R (Ω) is the distance between the two electrodes, the cross-sectional area of the test membrane and the test impedance.
As can be seen from the proton conductivity test result in fig. 4, the proton conductivity of the polyamide-6 dendritic nanofiber/Nafion composite membrane, the common polyamide-6 nanofiber/Nafion composite membrane, and the meta-aramid dendritic nanofiber/Nafion composite membrane is higher than that of the pure Nafion membrane at the same temperature. Particularly, at the temperature of 80 ℃, the sum of the proton conductivity of the dendritic polyamide-6 nano fiber/Nafion composite membrane, the proton conductivity of the common polyamide-6 nano fiber/Nafion composite membrane and the proton conductivity of the meta-aramid dendritic nano fiber/Nafion composite membrane is 0.287S cm-1、0.26S cm-1And 0.225S cm-1Far higher than 0.12(S cm) of pure Nafion membrane-1)。