KR102208306B1 - Composite ion exchange membrane comprising fluorinated polymer and sulfonated silica and method for producing the same - Google Patents

Abstract

A composite proton exchange membrane comprising a fluorine-based polymer and sulfonated silica, wherein the sulfonated silica is provided with a composite proton exchange membrane in which a sulfonic acid group is directly connected to the silica. The composite proton exchange membrane has excellent moisture absorption capacity, ion exchange capacity, and cation conductivity even in a low humidity environment, and has excellent mechanical properties and thermal stability.

Description

Composite ion exchange membrane comprising fluorinated polymer and sulfonated silica and method for producing the same}

It relates to a composite proton exchange membrane comprising a fluorine-based polymer and sulfonated silica, and a method for producing the same.

A fuel cell is an energy conversion device that directly converts chemical energy into electrical energy. It has higher energy density, power density, and conversion efficiency compared to conventional energy supply devices, and is an energy conversion device suitable for using hydrogen as an energy resource. Is considered. Among many types of fuel cells, proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) are in the spotlight as mobile device power supplies because they can be miniaturized and have excellent mechanical properties. PEMFC and DMFC are structurally the same, but are divided according to the fuel used. PEMFC uses hydrogen as fuel and DMFC uses methanol as fuel. In particular, the proton exchange membrane fuel cell (PEMFC) is considered as one of the promising energy conversion devices because it can be commercially used and applied in a wide range of fields such as portable devices, transportation systems, and power plants.

The ion exchange resin used in the proton exchange membrane fuel cell (PEMFC) is a synthetic resin capable of ion exchange. As proton exchange membranes using this material were developed, they were used in various fields electrochemically. Proton exchange membranes are widely used in fields such as fuel cells, redox flow cells, electrodialysis, desalination, ultrapure water and wastewater treatment. In particular, it is attracting worldwide attention as a clean technology to produce eco-friendly new and renewable energy by reducing the use of fossil fuels. Currently, due to the rapid increase in the use of electronic products such as small notebooks and mobile phones, research on the proton exchange membrane, which is a key material, is actively progressing in accordance with the need for development of high-life, high-capacity batteries and new fuel cells required for this.

The proton exchange membrane plays two main roles. The first is to electrically separate the anode and the cathode, and the second is to allow only protons to pass so that the fuel cell continuously generates electromotive force.

A representative commercial proton exchange membrane is Nafion. Nafion was synthesized by composing the backbone of the membrane with Teflon, a fluorine-based polymer, and reacting hydrophilic sulfonic acid (SO ^3- ) thereto. The backbone made of Teflon is hydrophobic, repelling water, and at the same time has relatively excellent mechanical properties and corrosion resistance. And sulfonic acids combine with water to form ion channels with an invert micelle structure, and these channels are connected to form a network. The protons separated from hydrogen by the catalyst layer on the cathode move to the anode along the network.

The proton exchange membrane is currently used exclusively by Nafion, which is supplied exclusively by DuPont. However, the low reliability of fuel cells is mostly due to the low mechanical, thermal, and chemical properties of the proton exchange membrane. The proton exchange membrane synthesized from a polymer material is easily torn due to the formation of pinholes or changes in motion conditions during operation, and degradation of performance due to deterioration occurs frequently. In addition, since it operates stably only at low temperatures below 80 ℃, it is difficult to supply fuel because high purity hydrogen must be used to avoid CO poisoning.

In addition, it is difficult to use the proton exchange membrane in a low humidity environment because of its low proton conductivity in a low humidity environment. Therefore, improving the performance of PEMFC in low humidity conditions has become important in terms of commercialization. The high performance of PEMFC can be obtained by controlling the humidity, but controlling the humidity for this causes additional cost.

Mauritz, K. A., and Moore, R. B. State of understanding of Nafion. Chemical Reviews 104, (2004), 4535-4585. Fuel Cell Fundamentals, Ryan O; Hayre et. al. John Wiley & Sons, New York. 978-0-470-25843-9

An object of the present invention is to provide a composite proton exchange membrane comprising a fluorine-based polymer and sulfonated silica to which a sulfonic acid group is directly connected to the silica.

In one aspect of the present invention

A composite proton exchange membrane comprising a fluorine-based polymer and sulfonated silica,

The sulfonated silica is provided with a complex proton exchange membrane to which a sulfonic acid group is directly connected to the silica.

In addition, in another aspect of the present invention

Synthesizing sulfonated silica to which a sulfonic acid group is directly linked to the silica from the silica precursor and the sulfonic acid compound;

Mixing the fluorine-based polymer and the synthesized sulfonated silica; And

There is provided a method for producing a composite proton exchange membrane comprising; casting the mixed fluorine-based polymer and sulfonated silica to form a composite proton exchange membrane.

In addition, in another aspect of the present invention

anode;

cathode;

The composite proton exchange membrane;

A membrane-electrode assembly comprising a is provided.

Furthermore, in another aspect of the present invention

A fuel cell including the membrane-electrode assembly is provided.

The composite proton exchange membrane provided in one aspect of the present invention has excellent moisture absorption capacity, ion exchange capacity, and cation conductivity even in a low humidity environment, and has excellent mechanical properties and thermal stability.

1 is a schematic diagram showing the chemical structure of a composite proton exchange membrane according to an embodiment of the present invention,
2 is a schematic diagram showing an example of a membrane-electrode assembly including a composite proton exchange membrane according to an embodiment of the present invention,
3 is a graph showing the FT-IR spectrum of pure silica and SSA according to an embodiment of the present invention,
Figure 4 shows the TEM image and EDS analysis results of SSA according to an embodiment of the present invention,
Figure 5 is a graph showing the XPS spectrum of SSA according to an embodiment of the present invention, Figure 5a is Si 2p, Figure 5b is O 1s, Figure 5c is shown for S 2p,
6 is a graph showing the results of tensile deformation experiments for the films of Examples and Comparative Examples of the present invention,
7 is a graph showing weight reduction according to temperature for the membranes of Examples and Comparative Examples of the present invention,
8 shows AFM images of the films of Examples and Comparative Examples of the present invention,
9 is an image showing a phase separation morphology for an embodiment and a comparative example of the present invention,
10 is a graph showing proton conductivity according to humidity conditions of the membranes of Examples and Comparative Examples of the present invention,
11 is a graph showing the proton conductivity according to the temperature conditions of the membranes of an embodiment and a comparative example of the present invention,
12 is a graph measuring the performance of a fuel cell according to Examples and Comparative Examples of the present invention,
13 is a graph measuring the performance of a fuel cell according to an embodiment of the present invention according to a humidity condition,
14 is a graph measuring the performance of a fuel cell according to another embodiment of the present invention according to a humidity condition,
15 is a graph measuring the performance of a fuel cell according to another embodiment of the present invention according to a humidity condition.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by an expert skilled in the art to which the present invention belongs. In general, the nomenclature used in this specification is well known and commonly used in the art.

In one aspect of the present invention

A composite proton exchange membrane comprising a fluorine-based polymer and sulfonated silica,

The sulfonated silica is provided with a complex proton exchange membrane to which a sulfonic acid group is directly connected to the silica.

Hereinafter, the composite proton exchange membrane provided in one aspect of the present invention will be described in detail for each material.

First, the composite proton exchange membrane provided in one aspect of the present invention includes a fluorine-based polymer.

The fluorine-based polymer may be a non-limiting example, perfluorosulfonic acid, polytetrafluoroethylene, or polyvinylidenefluoride, but is not limited thereto.

For example, perfluorosulfonic acid is preferred for use in proton exchange membranes due to its excellent mechanical stability, thermal stability and high ionic conductivity.

Next, the composite proton exchange membrane provided in one aspect of the present invention includes sulfonated silica.

The sulfonated silica may have a sulfonic acid group directly connected to the silica.

The sulfonated silica to which the sulfonic acid group is directly connected to the silica may have a higher proton conductivity compared to the sulfonated silica that is not.

In addition, the sulfonated silica may have a high ion exchange capacity (IEC) due to structural simplicity and interaction with the sulfonic acid group of the fluorine-based polymer despite the low content of the sulfonic acid group as the sulfonic acid group is directly connected to the silica.

Sulfonated silica to which a sulfonic acid group is directly connected to the silica has a structure as shown in Formula 1 below.

<Formula 1>

The sulfonated silica may be synthesized from a silica precursor and a sulfonic acid compound, but is not limited thereto, and may be synthesized from various precursors.

The silica precursor may be non-limiting examples, such as silica gel, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl ortho It may be a silicate (tetrabutyl orthosilicate) or tetraisopropyl orthosilicate (tetraisopropyl orthosilicate), but is not limited thereto.

The sulfonic acid compound may be, but is not limited to, chlorosulfuric acid (Cl-SO ₃ H), sulfuric acid (H ₂ SO ₄ ), or fuming sulfuric acid (oleum), but is not limited thereto. Does not.

The composite proton exchange membrane provided in one aspect of the present invention has the advantage that sulfonated silica can be obtained from a precursor having a relatively simple structure.

The sulfur content in the sulfonated silica may be 0.5 wt% to 3 wt%, 0.8 wt% to 2.5 wt%, and 1.0 wt% to 2.0 wt%.

The sulfonated silica may be included in 0.1 wt% to 2.0 wt%, preferably 0.2 wt% to 1.8 wt%, and more preferably 0.3 wt% to 1.6 wt% based on the fluorine-based polymer. And, even more preferably 0.4 wt% to 1.4 wt% may be included, and most preferably 0.5 wt% to 1.2 wt% may be included. When the content of the sulfonated silica is less than 0.1 wt% of the fluorine-based polymer, there is a problem that the interaction between the sulfonic acid group of the sulfonated silica and the sulfonic acid group of the fluorine-based polymer may not occur sufficiently, and exceeding 2.0 wt% In this case, fabrication of the composite film itself becomes difficult, and there is a problem that the overall performance of the film may decrease.

The sulfonated silica can be used as a filler in a proton exchange membrane, which can improve ionic conductivity in a low humidity environment.

In the case of the sulfonated silica having a sulfonic acid group directly connected to the silica as described above, the structure is very simple because the silica having a complex structure and the sulfonic acid precursor are not used, and this can allow the sulfonic acid group to be directly connected to the silica.

The sulfonic acid group of the sulfonated silica and the sulfonic acid group of the fluorine-based polymer can interact with each other, and the hydrophilic region can be reliably expanded due to the sulfonated silica composed of the simple chemical structure. have.

Since the expansion of the hydrophilic region brings about a contrasting effect with the hydrophobic region, a more reliable phase separation occurs, which is linked to the establishment of an ion channel, leading to an overall improvement of the ionic conductivity at all relative humidity.

Thermal stability and mechanical tensile strength may be improved due to the interaction between the sulfonic acid group of the sulfonated silica and the sulfonic acid group of the fluorine-based polymer.

The composite proton exchange membrane provided in one aspect of the present invention has a relatively well-separated phase morphology (see FIGS. 9b and 9d), and a well-organized phase separation between such hydrophobicity and hydrophilicity can promote proton transfer in the composite membrane. have.

In addition, the swelling degree is low compared to the excellent water uptake, so it can exhibit relatively excellent performance even in a low humidity environment.

In addition, the composite proton exchange membrane may have excellent mechanical properties and thermal stability.

In another aspect of the present invention

Synthesizing sulfonated silica to which a sulfonic acid group is directly linked to the silica from the silica precursor and the sulfonic acid compound;

Mixing the fluorine-based polymer and the synthesized sulfonated silica; And

There is provided a method for producing a composite proton exchange membrane comprising; casting the mixed fluorine-based polymer and sulfonated silica to form a composite proton exchange membrane.

Hereinafter, a method of manufacturing a composite proton exchange membrane provided in another aspect of the present invention will be described in detail for each step.

First, a method for preparing a composite proton exchange membrane provided in another aspect of the present invention includes synthesizing a sulfonated silica to which a sulfonic acid group is directly linked to the silica from a silica precursor and a sulfonic acid compound.

The silica precursor may be non-limiting examples, such as silica gel, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl ortho It may be a silicate (tetrabutyl orthosilicate) or tetraisopropyl orthosilicate (tetraisopropyl orthosilicate), but is not limited thereto.

The sulfonic acid compound may be, but is not limited to, chlorosulfuric acid (Cl-SO ₃ H), sulfuric acid (H ₂ SO ₄ ), or fuming sulfuric acid (oleum), but is not limited thereto. Does not.

The method may be performed by a sol-gel method, but is not limited thereto.

The step may include plastic working.

The plastic working step may be performed at a temperature of 100°C to 700°C, and preferably may be performed at a temperature of 200°C to 600°C, and more preferably at a temperature of 250°C to 550°C. And, most preferably, it can be carried out at a temperature of 300 ℃ to 500 ℃. The plastic processing may be performed while increasing the temperature in the above temperature range, and preferably, the temperature may be increased to a temperature of 3° C./min to 5° C./min.

The sulfonated silica may become a more powerful acidic material through the plastic processing.

In the step of synthesizing the sulfonated silica, the step of washing the sulfonated silica until neutralized may be further included, and the washing may be performed with DI water, but is not limited thereto.

The sulfur content in the sulfonated silica may be 0.5 wt% to 3 wt%, 0.8 wt% to 2.5 wt%, and 1.0 wt% to 2.0 wt%.

The step of synthesizing the sulfonated silica has an advantage that the precursor has a relatively simple chemical structure, and the sulfonated silica can be obtained relatively easily.

Next, a method for preparing a composite proton exchange membrane provided in another aspect of the present invention includes mixing a fluorine-based polymer and the sulfonated silica.

The fluorine-based polymer may be a non-limiting example, perfluorosulfonic acid, polytetrafluoroethylene, or polyvinylidenefluoride, but is not limited thereto.

For example, perfluorosulfonic acid is preferred for use in proton exchange membranes due to its excellent mechanical stability, thermal stability and high ionic conductivity.

The sulfonated silica may have a sulfonic acid group directly connected to the silica.

The sulfonated silica to which the sulfonic acid group is directly connected to the silica may have a higher proton conductivity compared to the sulfonated silica that is not.

Sulfonated silica to which a sulfonic acid group is directly connected to the silica has a structure as shown in Formula 1 below.

<Formula 1>

The sulfonated silica may be included in 0.1 wt% to 10 wt%, preferably 0.2 wt% to 5 wt%, more preferably 0.3 wt% to 3 wt% based on the fluorine-based polymer. And, even more preferably 0.5 wt% to 2 wt% may be included, and most preferably 0.6 wt% to 1.2 wt% may be included.

The sulfonated silica can be used as a filler in a proton exchange membrane, which can improve ionic conductivity in a low humidity environment.

The step of mixing the fluorine-based polymer and the sulfonated silica may include ultrasonicating the mixed fluorine-based polymer and the sulfonated silica, and stirring the mixture.

Next, a method for producing a composite proton exchange membrane provided in another aspect of the present invention includes forming a composite proton exchange membrane by casting the mixed fluorine-based polymer and sulfonated silica.

In the casting step, the mixture may be dried at a temperature of 50°C to 120°C. When the drying temperature is less than 30°C, there is a problem that it may be difficult to form a composite film, and when the drying temperature exceeds 150°C, there is a problem that cracks may occur or the thickness of the composite film may be non-uniform in the process of forming the composite film.

After the step, it may further include annealing the composite proton exchange membrane at a temperature of 80 ℃ to 100 ℃. The tensile strength of the composite proton exchange membrane may be improved by the annealing step.

In addition, after the step, it may further include a step of treating the complex proton exchange membrane with a sulfuric acid solution, and thereafter may be subjected to a step of washing. The washing may be performed with DI water, but is not limited thereto.

In another aspect of the present invention

anode;

cathode;

The composite proton exchange membrane;

A membrane-electrode assembly comprising a is provided.

Hereinafter, a membrane-electrode assembly provided in another aspect of the present invention will be described in detail for each configuration.

The positive electrode 10 and the negative electrode 10 are not particularly limited, since conventional ones can be used in the technical field to which the present invention pertains.

The anode and cathode include a gas diffusion layer 11 and a catalyst layer 12.

The catalyst layer includes a metal catalyst that promotes oxidation of hydrogen and reduction of oxygen. The catalyst layer is made of platinum, ruthenium, osmium, platinum-osmium alloy, platinum-palladium alloy, and platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn). It is preferable to include at least one selected from the group. In particular, it is preferred to include platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-cobalt alloy, platinum-nickel alloy, or mixtures thereof.

The metal catalyst is generally used while being supported on a carrier. The carrier may be a carbon-based material such as acetylene black or black salt; Alternatively, inorganic fine particles such as alumina and silica may be used. For example, the carrier supporting the catalyst has porosity and may have a surface area of 150 m 2 /g or more, specifically, 500 to 1200 m 2 /g, and an average particle diameter of 10 to 300 nm, specifically May be 20 to 100 nm.

Carbon paper or carbon cloth may be used as the gas diffusion layer, but is not limited thereto. The gas diffusion layer serves to support the electrode for the fuel cell, and serves to diffuse the reaction gas into the catalyst layer so that the reactive body can easily access the catalyst layer. It is preferable to use the gas diffusion layer obtained by water-repelling carbon paper or carbon cloth with a fluorine-based resin such as polytetrafluoroethylene. The water-repellent-treated carbon paper or carbon cloth may prevent the gas diffusion efficiency from being lowered by water generated when the fuel cell is driven.

The composite proton exchange membrane 20 may be applied to the above-described composite proton exchange membrane, and will not be described in duplicate.

The composite proton exchange membrane is located between the cathode and the anode.

In another aspect of the present invention

A fuel cell including the membrane-electrode assembly is provided.

The fuel cell may be applied to the above-described membrane-electrode assembly, and will not be described in duplicate.

Hereinafter, the present invention will be described in more detail through Examples, Comparative Examples and Experimental Examples. The scope of the present invention is not limited to specific embodiments, and should be interpreted by the appended claims. In addition, those who have acquired ordinary knowledge in this technical field should understand that many modifications and variations can be made without departing from the scope of the present invention.

<Example 1> Preparation of a composite membrane containing 0.5 wt% of SSA

A 100 mL beaker was charged with 10 mL of tetraethyl orthosilicate (TEOS) solution, and 1.0 mL of a Cl-SO ₃ H solution was added to the beaker. After stirring the mixed solution until a white gel was formed, the white gel was placed in a crucible and placed in a firing furnace. The temperature increase rate under atmospheric pressure was performed in the range of 300°C to 500°C at 4°C/min. After firing, the temperature was naturally lowered to 25°C, and the resulting material was washed with hot DI water until neutralized, and dried to obtain sulfonated silica (SSA).

Then, Nafion, a perfluorosulfonic acid membrane, was prepared. 0.5 wt% of SSA was added to the Nafion ionomer mixed with ethanol, and the mixture was sonicated for 1 hour. After the sonication was completed, the mixture was stirred for 3 hours using a magnetic bar. To obtain a composite membrane, the resulting mixture solution was poured into a plate culture dish and dried in a vacuum oven. In the solvent casting step, the composite membrane was dried at 50, 60, and 70°C for 1 hour and at 80°C for 4 hours. The composite membrane was further dried at 100° C. for 3 hours and then peeled off the plate. The membrane was treated with a 1M H ₂ SO ₄ solution boiled for 4 hours, and then washed several times with hot DI water.

<Example 2> Preparation of a composite membrane containing 1.0 wt% of SSA

A composite membrane was prepared in the same manner as in Example 1, but 1.0 wt% of SSA was added to the Nafion ionomer.

<Example 3> Preparation of a composite membrane containing 1.5 wt% of SSA

A composite membrane was prepared in the same manner as in Example 1, but 1.5 wt% of SSA was added to the Nafion ionomer.

<Comparative Example 1> Preparation of a composite membrane containing no SSA

A composite membrane was prepared in the same manner as in Example 1, but SSA was not added to the Nafion ionomer.

<Experimental Example 1> SSA characteristic analysis

In order to investigate the morphology of the sulfonated silica, for Example 2, a Fourier transform infrared (FT-IR) spectrum, a transmission electron microscope (TEM), a CHNS analyzer and an X-ray photoelectron spectroscopy (XPS) were used. An Agilent Cary 600 FT-IR spectrometer using an automatic sampler (> 6000 scans) was used to determine the vibration peaks of individual functional groups. The range was from 4000 to 500 cm ^-1 and the resolution was 4 cm ^-1 . In addition, a CHNS elemental analyzer (Elementar; Vario MACRO cube) and a TEM (FE-TEM, Hitachi HF-3300) energy dispersion spectroscopy (EDS) were used to check the element content of SSA.

Figure 3 shows the FT-IR spectrum of SAA compared to pure silica. The broad Si-O-Si (asymmetric) stretching and Si-O-Si (symmetric) stretching peaks of SiO ₂ appeared at 1000 to 1250 cm ^-1 and about 800 cm ^-1 , respectively. The asymmetrical Si-O-Si stretching peak and the symmetrical Si-O-Si stretching peak in the FT-IR spectrum of SSA also appeared in the same range as the FT-IR spectrum in the case of silica. Broadband OH stretching peaks appeared from 2700 to 3700 cm ^-1 . The fact that the stretching peaks of -SO ₃ H and SiO _{2 in} the FT-IR spectrum are formed in similar regions means that the -SO ₃ H and Si-O-Si peaks overlap each other in the 1250 to 1000 cm ^-1 region. The SO stretching peak of SSA appears at 667 cm ^-1 in FIG. 3B, and it can be seen that SSA was formed. This is a value consistent with the reported peak result of the SO of SSA.

From the EDS spectrum of FIG. 4, it can be seen that O, Si and S are included, and as a result of examining the sulfur content with a CHNS analyzer, the S content value was confirmed to be 1.65%.

In addition, when checking the XPS spectrum of FIG. 5, the peak of the Si 2p XPS spectrum of a wide range appeared in the range of 100-105 eV, and in the case of the O 1s XPS spectrum, near 528 to 535 eV due to Si-O and Si-OH. It shows a broadband peak of, and the S 2p peak was observed around 170 eV. This is due to the presence of -SO ₃ H in SSA. The FT-IR, EDS, CHNS and XPS results confirm that a sulfonic acid group was formed on the SiO ₂ surface, indicating that the sulfonated SiO ₂ was successfully synthesized.

<Experimental Example 2> Analysis of membrane properties

In order to measure the properties of the membrane for Examples 1 to 3 and Comparative Example 1, water absorption (water uptake, %), ion exchange capacity (ion, exchange capacity, IEC), swelling degree (%), mechanical properties, heat The membrane morphology such as stability (%) and membrane morphology was analyzed.

The moisture absorption rate was calculated from the weight of the film under dry (W _dry ) and wet (W _wet ) conditions. The weight of the wet film was obtained by immersing the sample in DI water for 1 day, then quickly removing the water on the surface of the film using tissue paper, and then measuring the weight of the wet sample. Then, the sample was dried in a vacuum oven at 100° C. for 3 hours to obtain a sample weight of the dried film. The calculation of the water absorption rate is as shown in Equation 1 below.

<Equation 1>

The ion exchange capacity (IEC) was determined by titration. A dry membrane was prepared to calculate the IEC value. The dried membrane (W _dry , mg) was immersed in 3M NaCl solution for one day, and then titrated with 0.01M NaOH solution (C _NaOH , M), and the volume of the NaOH solution used (V _NaOH , mL) was measured. The IEC value was calculated by Equation 2 below.

<Equation 2>

The degree of swelling can be calculated as in Equation 3 below by calculating the dimensional change of the membrane in dry (L _dry ) and wet (L _wet ) states.

<Equation 3>

In addition, in order to confirm the mechanical properties of the membrane, a sample size of 5 cm x 1.5 cm was measured using SFM-100 kN (United Testing Systems, USA).

Thermal stability was analyzed using a thermogravimetric analyzer (Thermo plus EVO, TG8120). The crucible containing the sample was heated, and the amount of the sample contained in the crucible exceeded 10 mg, and the temperature was adjusted at a rate of 20° C. min ⁻ in the range of room temperature to 900° C.

To analyze the morphology of the membrane, XE-15 (Park Systems, Korea), an atomic force microscope (AFM), which is a non-contact mode was used. The scan speed was 0.1 Hz and the X-Y scan size was 90 μm×90 μm.

Transmission electron microscopy (TEM, FEI Tecnai G2 F20) was used to investigate the phase separation morphology of the membrane. Before placing on the copper grid, the membrane sample was stained with 0.5 M aqueous lead acetate solution and gently washed with DI water. After the dyeing step, the membrane samples were dried in a vacuum oven for at least 4 hours. The dried sample was buried in an epoxy resin and cut with a Leica microtome. The thickness of the cut film sample was 80 nm.

The measurement results for this are shown in Table 1 below.

Moisture absorption rate
(%) Ion exchange capacity
(mEq g ^-One ) Degree of swelling
(%) Proton conductivity
(80℃, 20% RH, mS cm ^-One ) Proton conductivity
(80℃, 100% RH, mS cm ^-One ) Comparative example 17.3 ± 0.3 0.98 ± 0.03 13 5 111.4 Example 1
(SSA 0.5 wt%) 22.0 ± 1.3 1.20 ± 0.07 10 5.9 150.6 Example 2
(SSA 1.0 wt%) 24.1 ± 1.1 1.31 ± 0.07 9 8.8 230.1 Example 3
(SSA 1.5 wt%) 20.0 ± 0.4 1.11 ± 0.08 9 5.5 143.2

The ion exchange capacity (IEC) values of silica and SSA itself are 0.08 and 0.64 mEq g ^-1 , respectively, and SSA is more acidic than silica due to the presence of sulfonic acid groups.

As a result, Examples 1 to 3 have higher moisture absorption rates and IEC values compared to Comparative Example 1. As a result, Examples 1 to 3 show higher proton conductivity compared to Comparative Example 1, which is the same even in a low humidity environment.

On the other hand, it can be seen that Examples 1 to 3 have a lower degree of swelling compared to Comparative Example 1.

In particular, in the case of Example 2, it can be seen that the swelling degree is low while having the highest water absorption rate and ion exchange capacity.

Mechanical properties can be confirmed through FIG. 6. In Figure 6, it can be seen that as the content of SSA increases, the tensile strength increases. Each maximum stress is shown to be 16.3, 18.4 and 19.4 N for each of Examples 1 to 3. On the other hand, the maximum stress of Comparative Example 1 is 15.3 N. It can be seen that Examples 1 to 3 exhibit high maximum stress due to the interaction of Nafion and SSA, that is, the mechanical strength is improved.

In the case of elongation, Examples 1 to 3 show lower elongation compared to the comparative examples. The maximum elongation of Examples 1 to 3 and Comparative Example 1 was 5.6, 5.2, 4.6 and 6.5 mm, respectively. The maximum stress increases with increasing SSA content, but the maximum elongation decreases with increasing SSA content.

The maximum stress of the Nafion-SSA composite film improved as the SSA content of the composite film increased, but the aspect of the maximum elongation of the Nafion-SSA composite film showed a lower value than that of the modified Nafion. Water absorption and IEC values of the Nafion-SSA composite membrane were higher than that of the modified Nafion, but the degree of swelling of the Nafion-SSA composite membrane was lower than that of the reconstituted Nafion, which means that SSA interacts with the Nafion backbone.

7 shows the thermal stability of the films of Examples 1 to 3 and Comparative Example 1. All membranes exhibit three reduction steps: dehydration (56-160 °C), desulfurization (270-420 °C) and polymer backbone decomposition (400-550 °C).

However, in the case of the composite membranes of Examples 1 to 3, it can be seen that the degree of weight reduction in the desulfurization step is smaller than that of Comparative Example 1. Sulfonated fillers such as SSA have improved thermal stability due to the interaction between the sulfonated filler and the sulfonic acid group of the polymer. The composite membranes of Examples 1 to 3 exhibit improved thermal stability, meaning that the sulfonic acid groups of Nafion and SSA interact chemically with each other. In addition, this interaction has a positive effect on the thermal stability of the composite membranes of Examples 1 to 3, especially in the decomposition step of the polymer backbone. These thermal stability properties are in good agreement with tensile strain test results and phase separation morphology.

8 shows AFM images of Examples 1 to 3 and Comparative Example 1. 8A is an AFM image of Comparative Example 1, FIG. 8B is Example 1, FIG. 8C is Example 2, and FIG. 8D is Example 3. Example 3 shows a larger Rq value (255 nm) and a larger degree of aggregation compared to Examples 1 and 2. This means that although SSA is well dispersed in the Nafion ionomer solution mixed with ethanol, SSA is easily solidified in the casting step. Rq values of Examples 1 to 3 are 65.6, 142, and 255 nm, respectively, and in Comparative Example 1, they are 5.40 nm. That is, as the SSA content increases, the Rq value increases, and it can be seen that there is a very large difference in Example 3 compared to Example 2. This will be the reason for the rapid decrease in the proton conductivity of the composite membrane in Example 3 compared to Example 2.

9 shows the phase separation morphology through SEM of Comparative Examples 1 and 2. 9A and 9C show a case of Comparative Example 1, and FIGS. 9B and 9D show a case of Example 2. The bright regions represent the hydrophobic regions and the dark regions represent the hydrophilic regions containing the sulfonated lead groups. In the case of Example 2, compared to Comparative Example 1, significant phase separation can be confirmed. Particularly, in the case of Example 2, it can be seen that SSA can interact with the sulfone group of Nafion because it has a clearer and larger hydrophilic portion compared to Comparative Example 1. This makes it possible to exhibit higher proton conductivity and good thermal properties.

<Experimental Example 3> Proton conductivity analysis

Proton conductivity was measured for Examples 1 to 3 and Comparative Example 1. It was measured by a four-probe measurement method using a membrane conductive cell (Bekktech, Korea). The membrane sample was placed in a conductive cell and contacted with two platinum electrodes separated by a fixed distance, and a specific voltage was applied between the two Pt electrodes to obtain a corresponding current in a potentiostat. The measurement of the film conductivity according to RH at 80° C. is shown in Equation 4 below.

<Equation 4>

Here, R is the resistance of the film (Ω), T is the thickness of the film (cm), W is the width of the sample (cm), and L (cm) is the distance between the two Pt electrodes (L = 0.425 cm).

The measured values are shown in FIG. 9. It was measured while changing the humidity to 20 ~ 100% under 80 ℃. Examples 1 to 3 showed higher proton conductivity than Comparative Example 1 in the entire RH range, and Examples 1 and 3 showed similar proton conductivity. In addition, Example 2 showed the highest proton conductivity, and showed about 1.7 times superior proton conductivity compared to Comparative Example 1 under a 20% RH condition. In the case of Examples 1 to 3, due to the high IEC value, SSA having a sulfonic acid group by itself exhibits high proton conductivity even under low RH conditions.

Activation energies of Comparative Examples 1 and 2 were measured as 8.20 and 7.70 kJ mol ^-1 , respectively (see FIG. 11), through which SSA interacts with Nafion ionomer, resulting in low activation energy values and high proton conductivity. You can see that you have.

<Experimental Example 4> Fuel cell characteristic analysis

With respect to Examples 1 to 3 and Comparative Example 1, a membrane electrode assembly (MEA) having an active region of 5 cm ^{2 was prepared} to evaluate fuel cell performance. MEA was added between Teflon sealing gaskets and inserted into a single cell. The flow rates of hydrogen and oxygen gas were fixed at 300 SCCM and the cell temperature was 80°C. To control specific RH conditions, the anode and cathode inlet portions were heated to a dew point temperature. After stabilizing the MEA at 0.6 V under various conditions of RH, the fuel cell performance of all MEAs was measured without applying back pressure.

The result values under the conditions of 25% RH and 80°C are shown in FIG. 12. Examples 1 to 3 show superior performance compared to Comparative Example 1. The maximum power densities of Examples 1 to 3 are 293, 454, and 223 mW cm ^-2 , respectively, and Example 2 has a value 2.85 times higher than that of Comparative Example 1 (159 mW cm ^-2 ). The current densities of Examples 1 to 3 at 0.2 V were 1146, 2062 and 885 mA cm ^-2, respectively. Example 2 has a value 2.81 times higher than that of Comparative Example 1 (734 mA cm ^-2 ). In addition, in the case of Example 2, the HFR value is the lowest, and thus the performance of the fuel cell may be the best.

For Examples 1 to 3, measurement values of fuel cells under 25, 50, and 75% RH conditions are shown in FIGS. 13 to 15, respectively. It can be seen that the case of Example 2 has the highest fuel cell performance under all RH conditions.

10 electrodes
11 Gas diffusion layer
12 catalyst bed
20 proton exchange membrane

Claims (11)

A composite proton exchange membrane comprising a fluorine-based polymer and sulfonated silica,
The sulfonated silica is a sulfonic acid group directly connected to the silica,
The sulfonated silica is contained in an amount of 0.5 wt% to 1.5 wt% based on the fluorine-based polymer,
Complex proton exchange membrane, characterized in that the root mean square roughness (Rq) is 65.6 to 225 nm as measured by an atomic force microscope (AFM).
The method of claim 1,
The fluorine-based polymer is a complex proton exchange membrane, characterized in that at least one selected from the group consisting of perfluorosulfonic acid, polytetrafluoroethylene, and polyvinylidenefluoride.
delete Synthesizing sulfonated silica to which a sulfonic acid group is directly linked to the silica from the silica precursor and the sulfonic acid compound;
Mixing the fluorine-based polymer and the synthesized sulfonated silica; And
Forming a complex proton exchange membrane by casting the mixed fluorine-based polymer and sulfonated silica; includes,
The fluorine-based polymer is mixed with ethanol,
The sulfonated silica is mixed with 0.5 wt% to 1.5 wt% based on the fluorine-based polymer.
The method of claim 4,
The silica precursor is silica gel, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate And tetraisopropyl orthosilicate (tetraisopropyl orthosilicate) at least one member selected from the group consisting of a composite proton exchange membrane manufacturing method.
The method of claim 4,
The sulfonic acid compound is characterized in that at least one selected from the group consisting of chlorosulfuric acid (Cl-SO ₃ H), sulfuric acid (H ₂ SO ₄ ) and fuming sulfuric acid (oleum). Composite proton exchange membrane manufacturing method.
The method of claim 4,
Synthesizing the sulfonated silica to which the sulfonic acid group is directly connected to the silica from the silica precursor and the sulfonic acid compound comprises plastic working.
The method of claim 4,
The fluorine-based polymer is one or more selected from the group consisting of perfluorosulfonic acid, polytetrafluoroethylene, and polyvinylidenefluoride.
The method of claim 4,
After the step of forming a complex proton exchange membrane by casting the mixed fluorine-based polymer and sulfonated silica,
Annealing the composite proton exchange membrane at a temperature of 100°C to 150°C.
anode;
cathode;
The composite proton exchange membrane of claim 1;
Membrane-electrode assembly comprising a.
A fuel cell comprising the membrane-electrode assembly of claim 10.

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