KR102602007B1 - Poly(isatin-phenylene) based polymer for electrolyte of fuel cell, polymer electrolyte for fuel cell, and fuel cell comprising the same - Google Patents

Abstract

This relates to a polymer for fuel cell electrolyte represented by structural formula 1 below and a polymer electrolyte containing the same. As a result, the poly(isatin-phenylene)-based polymer for fuel cell electrolytes of the present invention and the polymer electrolyte membrane for fuel cells containing the same can replace the conventional Nafion electrolyte membrane, which is not environmentally friendly and has a high manufacturing cost, while maintaining proton conductivity and thermal stability. , power density can be maintained at an excellent level.
[Structural Formula 1]

Description

Poly(isatin-phenylene) based polymer for fuel cell electrolyte, polymer electrolyte for fuel cell containing same, and fuel cell {POLY(ISATIN-PHENYLENE) BASED POLYMER FOR ELECTROLYTE OF FUEL CELL, POLYMER ELECTROLYTE FOR FUEL CELL, AND FUEL CELL COMPRISING THE SAME}

The present invention relates to polymers for fuel cell electrolytes, polymer electrolytes for fuel cells containing the same, and fuel cells. More specifically, the present invention relates to polymers for fuel cell electrolytes, and more specifically, to improve ion exchange capacity, proton conductivity, and thermal stability by modifying poly(isatin-phenylene)-based polymers. It relates to poly(isatin-phenylene)-based polymers for fuel cell electrolytes that can be improved, polymer electrolytes for fuel cells containing the same, and fuel cells.

Over the past decades, fuel cells have received great attention due to their high efficiency and low polluting emissions. Additionally, the unique cell structure facilitates package sizing for application in portable devices and transport for large-scale power storage. Especially in the transportation industry, its use is becoming increasingly frequent among domestic and foreign automobile manufacturers such as Hyundai, Toyota, Honda, and Mercedes. Such fuel cells were commercialized early due to their wide operating temperature and excellent performance. Nevertheless, global commercialization of polymer electrolyte fuel cells (PEMFCs) is still limited by manufacturing costs and durability.

This barrier is largely influenced by the conductive electrolyte membrane, which is accepted as a key component of the membrane electrode assembly (MEA) and the heart of the polymer electrolyte membrane fuel cell (PEMFC).

Currently, perfluorinated sulfonic acid (PFSA) membranes such as Nafion®, Aciplex® and Flemion® are the most preferred conducting electrolyte materials for PEMFCs due to their significantly improved mechanical and chemical stability and excellent proton conductivity below 90°C.

However, PFSA membranes also have several disadvantages: high manufacturing cost, low proton conductivity at low humidity, and chemical decomposition at high temperatures.

As a result, sulfonated hydrocarbon polymers were introduced to balance cost and fuel cell performance at high temperatures.

Additionally, since these polymers can be linked to various functional groups, the membrane degradation problem can be solved to some extent through the recommended molecular design.

Additionally, hydrocarbon membranes can be synthesized through conventional methods, which are more cost-effective than PFSA membranes. However, the application of hydrocarbon membranes is limited. For example, proton transport may be inhibited at low humidity due to narrow channels formed by hydrophobic and hydrophilic microphases.

Moreover, beyond a certain degree of sulfonation, the electrolyte membrane tends to absorb large amounts of water, which reduces the chemical and mechanical stability of the membrane. To overcome these factors, random, block, and graft copolymers were analyzed to improve the chemical and mechanical stability of pure hydrocarbon membranes.

However, further efforts are still needed to improve the proton conductivity and dimensional stability of hydrocarbon membranes.

Korean Patent Publication No. 2013-0047650 U.S. Patent Publication No. 2013-660068

The purpose of the present invention is to provide a poly(isatin-phenylene)-based polymer for fuel cell electrolytes that can replace the conventional Nafion electrolyte membrane, which is not environmentally friendly and has a high manufacturing cost, while maintaining proton conductivity, thermal stability, and power density at excellent levels. , to provide a polymer electrolyte for fuel cells and a fuel cell containing the same.

According to one aspect of the present invention,

A polymer for fuel cell electrolyte represented by the structural formula 1 below is provided.

[Structural Formula 1]

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are the same or different from each other and are each independently a hydrogen atom or a C1 to 20 alkyl group,

R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C20 chloroalkyl group, or a C1 to C20 fluoroalkyl group,

R ⁷ is a C1 to 20 alkyl group.

Preferably,

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are the same or different from each other, and each independently represents a hydrogen atom or a C1 to 10 alkyl group,

R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C10 chloroalkyl group, or a C1 to C10 fluoroalkyl group,

R ⁷ may be a C1 to 10 alkyl group.

More preferably,

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are hydrogen atoms,

R ⁴ to R ⁶ are the same as or different from each other and are each independently a fluorine group,

R ⁷ is a methyl group,

The compound represented by Structural Formula 1 may have a weight average molecular weight (Mw) of 50,000 to 200,000.

According to another aspect of the present invention,

(a) preparing poly(isatine-phenylene) by reacting N-alkyl isatin and biphenyl in an organic solvent under a superacid catalyst;

(b) dissolving the polyisatin phenylene in an organic solvent and reacting it with chlorosulfonic acid to prepare sulfonated polyisatin phenylene;

(c) reacting the sulfonated polyisatin phenylene with thionyl chloride to produce chlorinated polyisatin phenylene; and

(d) reacting the chlorinated polyisatin phenylene with sulfamoyl halide to prepare a compound represented by the following structural formula 1. A method for producing a polymer for a fuel cell electrolyte is provided, including:

[Structural Formula 1]

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are the same or different from each other and are each independently a hydrogen atom or a C1 to 20 alkyl group,

R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C20 chloroalkyl group, or a C1 to C20 fluoroalkyl group,

R ⁷ is a C1 to 20 alkyl group.

In step (a),

The N-alkyl isatin may be any one selected from N-methyl isatin, N-ethyl isatin, N-propyl isatin, and N-butyl isatin.

In step (a),

The superacid catalyst is trifluoromethanesulfonic acid (TFSA), Fluorosulfuric acid, Trifluoromethanol, Carborane acid, and Chlorosulfonic acid. acid), and fluoroboric acid (Tetrafluoroboric acid).

The N-alkyl isatin of step (a) can be prepared by reacting isatin with an alkyl halide in an organic solvent.

The organic solvent may be any one selected from dimethyl carbonate (DMC), dichloromethane (DCM), acetonitrile (ACN), trichloromethane (TCM), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC). there is.

The reaction in step (b) may be carried out at a temperature of 20 to 30°C.

The reaction in step (b) may be carried out under an inert gas atmosphere.

The reaction in step (c) may be performed at a temperature of 50 to 70°C.

The reaction in step (c) may be carried out under an inert gas atmosphere.

In step (d), the sulfamoyl halide is selected from sulfamoyl fluoride, sulfamoyl chloride, sulfamoyl bromide and sulfamoyl iodide. It can be any one selected.

The reaction of step (d) may be carried out at a temperature of 20 to 30°C.

According to another aspect of the present invention,

A polymer electrolyte membrane for fuel cells containing the polymer for fuel cell electrolytes is provided.

The polymer electrolyte membrane for a fuel cell may be a blended membrane that additionally includes poly(isatin-phenylene) to which a sulfonic acid group (-SO ₃ H) is bonded.

According to another aspect of the present invention,

A method for manufacturing a polymer electrolyte membrane for a fuel cell, including a method for manufacturing the polymer for a fuel cell electrolyte, is provided.

According to another aspect of the present invention,

A fuel cell including the polymer electrolyte membrane for a fuel cell is provided.

According to another aspect of the present invention,

An electrical device including the fuel cell is provided.

The electrical device may be any one selected from a communication device, a transportation device, an energy storage device, and an acoustic device.

The poly(isatin-phenylene)-based polymer for fuel cell electrolyte of the present invention, and the polymer electrolyte membrane for fuel cells containing the same, can replace the conventional Nafion electrolyte membrane, which is not environmentally friendly and has a high manufacturing cost, and has excellent proton conductivity, thermal stability, and power density. can be maintained at an excellent level.

Figure 1 is a reaction scheme showing the manufacturing process of the poly(isatin-phenylene)-based polymer of Example 1.
Figure 2 shows the 1H NMR analysis results of N-methyl isatin in Experimental Example 1.
Figure 3 shows the results of 1H NMR analysis of PiP in Experimental Example 1.
Figure 4 shows the results of 1H NMR analysis of SPiP in Experimental Example 1.
Figure 5 shows the 1H NMR analysis results of SIPiP in Experimental Example 1.
Figure 6 shows the FT-IR analysis results of Experimental Example 2.
Figure 7 shows the measurement results by thermogravimetric analysis (TGA) of Experimental Example 3.
Figure 8 shows the results of analysis of cell characteristics of the electrolyte membrane according to Experimental Example 4.
Figures 9 and 10 show the results of measuring the proton conductivity of the membrane according to Experimental Example 5.
Figure 11 shows the stability measurement results of the electrolyte membrane according to Experimental Example 6.
Figure 12 shows the results of atomic force microscopy (AFM) image analysis of Experiment Example 7.
Figure 13 shows the results of electrochemical characteristic analysis of the fuel cell according to Experimental Example 8.
Figure 14 is a schematic diagram showing the form and characteristics of the poly(isatin-phenylene) polymer to which a sulfone imide group is bonded according to the present invention.

Below, various aspects and various embodiments of the present invention are described in more detail. Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the following description is not intended to limit the present invention to specific embodiments, and in describing the present invention, if it is determined that a detailed description of related known technology may obscure the gist of the present invention, the detailed description will be omitted. . The terminology used herein is only used to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, or a combination thereof described in the specification, but are not intended to indicate the presence of one or more other features or It should be understood that this does not exclude in advance the possibility of the presence or addition of numbers, steps, operations, components, or combinations thereof.

Hereinafter, the poly(isatin-phenylene)-based polymer for fuel cell electrolyte of the present invention will be described.

The poly(isatin-phenylene)-based polymer for fuel cell electrolyte of the present invention is represented by the structural formula 1 below.

[Structural Formula 1]

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are the same or different from each other and are each independently a hydrogen atom or a C1 to 20 alkyl group,

R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C20 chloroalkyl group, or a C1 to C20 fluoroalkyl group,

R ⁷ is a C1 to 20 alkyl group.

Preferably,

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are the same or different from each other, and each independently represents a hydrogen atom or a C1 to 10 alkyl group,

R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C10 chloroalkyl group, or a C1 to C10 fluoroalkyl group,

R ⁷ may be a C1 to 10 alkyl group.

More preferably,

In structural formula 1,

n is the number of repeat units,

R ¹ to R ³ are hydrogen atoms,

R ⁴ to R ⁶ are the same as or different from each other and are each independently a fluorine group,

R ⁷ is a methyl group,

The compound represented by Structural Formula 1 may have a weight average molecular weight (Mw) of 50,000 to 200,000, preferably 80,000 to 160,000, and more preferably 100,000 to 130,000.

Hereinafter, the method for producing the poly(isatin-phenylene)-based polymer for fuel cell electrolyte of the present invention will be described.

First, N-alkyl isatin and biphenyl are added to an organic solvent and reacted under a superacid catalyst to produce poly(isatine-phenylene) (step a).

The N-alkyl isatin may be any one selected from N-methyl isatin, N-ethyl isatin, N-propyl isatin, and N-butyl isatin, and is preferably N-methyl isatin or N-ethyl isatin. It may be isatin, more preferably N-methyl isatin.

The superacid catalyst is trifluoromethanesulfonic acid (TFSA), Fluorosulfuric acid, Trifluoromethanol, Carborane acid, and Chlorosulfonic acid. acid), fluoroboric acid, etc., and preferably trifluoromethanesulfonic acid (TFSA).

The N-alkyl isatin can be prepared by reacting isatin with an alkyl halide in an organic solvent.

The organic solvent may be dimethyl carbonate (DMC), dichloromethane (DCM), acetonitrile (ACN), trichloromethane (TCM), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC).

Next, the polyisatin phenylene is dissolved in an organic solvent and reacted with chlorosulfonic acid to prepare sulfonated polyisatin phenylene (step b).

In this step, the reaction is preferably performed at a temperature of 20 to 30°C, more preferably 22 to 27°C, and even more preferably 24 to 26°C.

Additionally, the reaction is preferably performed under an inert gas atmosphere. The inert gas includes group 18 elements such as helium (He), neon (Ne), and argon (Ar), as well as nitrogen (N ₂ ), and more preferably, the operation may be performed in a nitrogen gas atmosphere.

Thereafter, the sulfonated polyisatin phenylene is reacted with thionyl chloride to prepare chlorinated polyisatin phenylene (step c).

In this step, the reaction is preferably performed at a temperature of 50 to 70°C, more preferably 53 to 67°C, and even more preferably 58 to 62°C.

Additionally, the reaction is preferably performed under an inert gas atmosphere. The inert gas includes group 18 elements such as helium (He), neon (Ne), and argon (Ar), as well as nitrogen (N ₂ ), and more preferably, the operation may be performed in a nitrogen gas atmosphere.

Next, the chlorinated polyisatin phenylene is reacted with sulfamoyl halide to prepare a compound represented by the following structural formula 1 (step d).

The sulfamoyl halide may be any one selected from sulfamoyl fluoride, sulfamoyl chloride, sulfamoyl bromide, and sulfamoyl iodide. Preferably, it may be sulfamoyl fluoride or sulfamoyl chloride, and even more preferably, it may be sulfamoyl fluoride.

In this step, the reaction is preferably performed at a temperature of 20 to 30°C, more preferably 22 to 27°C, and even more preferably 24 to 26°C.

In addition, the present invention provides a polymer electrolyte membrane for fuel cells containing the poly(isatin-phenylene)-based polymer for fuel cell electrolytes.

Additionally, the present invention provides a method for producing a polymer electrolyte membrane for fuel cells, including a method for producing a poly(isatin-phenylene)-based polymer for a fuel cell electrolyte.

Additionally, the present invention provides a fuel cell including the polymer electrolyte membrane for fuel cells.

Additionally, the present invention provides an electric device including the fuel cell.

The electrical device may be a communication device, a transportation device, an energy storage device, an acoustic device, etc.

Hereinafter, the present invention will be described in detail through examples.

[Example]

Figure 1 is a reaction scheme showing the manufacturing process of the poly(isatin-phenylene)-based polymer of Example 1. Hereinafter, the manufacturing process of the poly(isatin-phenylene)-based polymer of Example 1 will be described with reference to Scheme 1.

Preparation Example 1: Synthesis of N-methyl isatin

Acetonitrile (131.5 mL) was mixed with isatin (5.00 g, 33.98 mmol), potassium carbonate (5.64 g, 40.78 mmol), and methyl iodide (2.54 mL, 40.78 mmol) to make 250 mL 1- It was placed in an old flask, equipped with a condenser, and refluxed in a N ₂ atmosphere at 80° C. for 24 hours. The mixture was filtered and the filtrate was evaporated under reduced pressure. Afterwards, the obtained red solid was dissolved in DMC and filtered again to remove residual salts. After further evaporation, crude red N-methylisatin was obtained. Ethanol was used for purification and the resulting monomer was dried in a vacuum oven at 80 °C overnight. As a result, red crystalline N-methylisatin (5.23 g) was obtained with a yield of 95.66%.

Preparation Example 2: Synthesis of sulfamoyl fluoride

The sulfamoyl fluoride synthesis apparatus consists of a 250 mL 1-neck flask, a condenser, and a dean stark trap. Antimony trifluoride (22.10 g, 123.65 mmol) and chlorosulfonyl isocyanate (50.00 g, 353.28 mmol) were added to a one-neck flask and stirred at room temperature. To prevent leakage, the entire system was sealed with Teflon tape and silver foil, and then a Dean-Stark trap and condenser were installed. The mixture was stirred rapidly at 80° C. for 24 hours under N ₂ gas to collect a clear liquid (40.40 g) in a Dean Stark trap. The intermediate product was transferred to a 250 mL two-necked flask equipped with a condenser, and formic acid (18.10 mL, 479.69 mmol) was added dropwise at 0°C. Afterwards, all materials were reacted at room temperature under N ₂ for 15 hours. The condenser was quickly removed and sulfamoyl fluoride (12.68 g) was collected through the pre-installed distillation system at 65°C for 4 hours.

Preparation Example 3: Precursor polyisatin phenylene (PiP) polymerization

PiP, a precursor polymer, was prepared from biphenyl and N-methyl isatin prepared according to Preparation Example 1 through the Friedel-Crafts reaction using the superacid trifluoromethanesulfonic acid (TFSA) as a catalyst. A mixture of N-methyl isatin (6.50 g, 40.36 mmol), biphenyl (5.18 g, 33.63 mmol) and DMC (16.40 mL) was placed in a 100 mL 2-necked flask equipped with a mechanical stirrer. TFSA (50 g) was added dropwise to the flask under freezing conditions. Next, the reaction vessel was maintained at room temperature until a highly viscous dark red solution was formed. The viscous solution was slowly poured into methanol to extract the resulting polymer, and the precipitate was washed repeatedly with methanol and deionized water until the solution became neutral. After filtration, it was dried overnight in an oven at 60°C to obtain a white polymer (9.70g).

Preparation Example 4: Preparation of sulfonation polyisatin phenylene (SPiP)

For the sulfonated polymer (SPIP), PiP (5.00 g, 16.81 mmol) prepared in Preparation Example 3 was completely dissolved in DMC (50 mL) at room temperature, and chlorosulfonic acid (8.94 mL) was added to a round flask in an ice bath. It was obtained by adding dropwise to . The solution was stirred under N ₂ for 2 hours and 30 minutes at room temperature and slowly transferred to deionized water to extract the sulfonate polymer and remove residual acid. The resulting SPiP was filtered and washed repeatedly with deionized water until it became neutral. Finally, pink SPiP (8.56 g) was obtained after drying in an oven at 60 °C overnight.

Example 1: Preparation of chlorination and sulfonimide-conjugated polyisatin phenylene (SIPiP)

SPiP (5.00 g, 9.30 mmol) and thionyl chloride (60 mL) prepared in Preparation Example 4 were added to a 250 mL two-necked flask equipped with a condenser and stirred rapidly at 60°C under N ₂ for 24 hours. . The crude chlorinated polymer was evaporated to remove the solvent and washed with DMC approximately twice to remove impurities. After evaporation, DMC (50 mL) and pyridine (2 drops) were added as solvent and catalyst, respectively. Then, a solution of sulfamoyl fluoride (3.30 g, 33.5 mmol) dissolved in DMC (15 mL) was added dropwise to the reaction mixture in an ice bath. After stirring at room temperature for 24 hours, the mixture was poured into 500 mL of deionized water and filter-dried in an oven at 60°C overnight to obtain SIPIP, a white polymer.

Example 2: Preparation of SIPiP electrolyte membrane

The electrolyte membrane was manufactured by dissolving the polymer in NMP and casting it on a glass plate with a square silicon module. The blending membrane was prepared through a simple casting method. SIPiP was clearly dissolved in NMP, mixed, and stirred at 60°C to obtain a uniform solution. After casting the polymer solution on a glass plate, the solution on the glass plate was placed in an oven at 80°C for 24 hours to remove NMP, and the film thickness was ensured to be within 100 ± 20 mm.

Example 3: Preparation of SPiP + SIPiP blended electrolyte membrane

An electrolyte membrane was manufactured under the same conditions as in Example 2, except that SIPiP was not used alone, but SPiP and SIPiP were mixed in equal amounts.

Comparative Example 1: Preparation of PiP electrolyte membrane

An electrolyte membrane was manufactured under the same conditions as in Example 2, except that PiP was used instead of SIPiP.

Comparative Example 2: SPiP Electrolyte membrane manufacturing

An electrolyte membrane was manufactured under the same conditions as Example 2, except that SPiP was used instead of SIPiP.

[Test example]

Experimental Example 1: NMR analysis

Figure 2 shows the 1H NMR analysis results of N-methyl isatin prepared according to Preparation Example 1.

According to this, it was confirmed that N-methyl isatin monomer was successfully synthesized from isatin and methyl iodide. Four phenyl protons appeared at 6.90 - 7.46 ppm, and a new notable CH ₃ proton shift was found at 3.29 ppm, which was also consistent with previous studies.

The chemical structure of sulfamoyl fluoride was confirmed by 19F NMR and 1H NMR, the fluorine peak was observed at 59 ppm and the proton peak was observed at 8.12 ppm.

Meanwhile, the precursor polymer PiP was synthesized through a super acid-catalyzed polyhydroxy-alkylation reaction using N-methyl isatin and biphenyl. The mechanism of Brønsted or Lewis strong acids interacting with electrophiles has been described by Olah et al. Briefly, the carbonyl and amine groups present in N-methyl isatin are protonated by TFSA to form a superelectrophilicity, and then a new carbon-carbon bond is created through the superelectrophilic reaction with the electron-rich biphenyl. . Moreover, since the polymerization rate is highly dependent on the amount of N-methylisatin, a little extra N-methylisatin was added to the polymerization to increase the reaction rate and the molecular weight of PiP. However, excessive monomer can cause cross-linking of the polymer. Therefore, the excess of N-methyl isatin was always maintained at 120% of biphenyl.

Figure 3 shows the results of 1H NMR (dissolved in CDCl ₃ ) analysis of PiP prepared according to Preparation Example 3. According to this, in PiP, 4 protons and 8 protons of methyl isatin and phenyl group were detected between 6.91 and 7.46 ppm, and methyl protons still appeared at 3.29 ppm.

Afterwards, SPiP was prepared from PiP and chlorosulfonic acid at room temperature. Reaction time and acid amount play a very important role in producing highly sulfonated polymers. Since excessive reaction time causes the sulfonated polymer to dissolve in water, the reaction time was controlled within 3 hours.

Figure 4 shows the results of 1H NMR analysis of SPiP prepared according to Preparation Example 4. Compared to the PiP NMR results in Figure 3, a new signal appeared at 4.25 ppm, which corresponds to the sulfone group, and it can be confirmed that the sulfone group successfully reacted with the polymer. SIPiP is synthesized through two steps. In the chlorination process of polymers, the airtight reaction plays an important role in preventing the substitution of Cl with H by preventing contact between the reactants and moisture.

Figure 5 shows the 1H NMR analysis results of SIPiP prepared according to Example 1. According to this, three methyl isatin protons and six phenyl group protons were still detected at 6.9 - 7.2 ppm.

Experimental Example 2: FT-IR and GPC analysis

Figure 6 shows the results of FT-IR analysis for the PiP of Preparation Example 3 and the SIPiP of Example 1. According to this, the sulfonic group signal is replaced by the imide proton signal at 8.85 ppm. SIPiP can also be confirmed in FT-IR. The characteristic absorption bands of sulfonimide are indicated at 1300 cm ^-1 and 1113 cm ^-1 at -S=O stretching vibration. The broad peak at 3500 cm ^-1 was assigned to the -NH stretching vibration of the water molecules around the sulfonimide group and the sulfonimide, and the bending vibration of -NH was combined with the -C = O stretching vibration at 1693 cm ^-1 . observed together. 1H NMR and FT-IR data as described above show successful synthesis of both monomer and polymer.

The molecular weight of a polymer can be confirmed through GPC (Gel Permeation Chromatography). According to this, PiP of Preparation Example 3 showed a weight average molecular weight (Mw) in the range of 39,000 to 58,000, and SPiP showed an Mw in the range of 86,000 to 94,000. The Mw of SIPiP was found to be 110,000 to 122,000.

Experimental Example 3: Thermogravimetric Analysis of Electrolyte Membrane

The stability of the electrolyte membranes prepared according to Examples 2 and 3 and Comparative Examples 1 and 2, respectively, was measured by thermogravimetric analysis (TGA), and the results are shown in FIG. 7. According to this, the PiP electrolyte membrane of Comparative Example 1 was stable up to 430°C. However, the SPiP electrolyte membrane of Comparative Example 2 begins to lose weight at about 170 °C due to sulfonic acid groups, and the second decomposition from 525 °C to 800 °C corresponds to the weight loss of the main polymer backbone.

In addition, in the case of the SIPiP electrolyte membrane of Example 2, a 5% weight loss was detected before 200°C, which is due to the evaporation of moisture absorbed during the sample processing process, and this shows that the SIPiP electrolyte membrane exhibits hygroscopicity. In particular, sulfonimide decomposition began around 275 °C, almost 100 °C higher than the sulfonic acid decomposition temperature. Meanwhile, the weight loss curve of the blended electrolyte membrane of Example 3 is very similar to the weight loss curve of the SPiP electrolyte of Comparative Example 2, and the weight loss is around 170 ℃ and 475 ℃, which represents the decomposition temperature of acid groups and main polymer chains. was observed.

Overall, the TGA results showed that SPiP, SIPiP, and blended electrolyte membranes exhibited thermal stability well above the operating temperature range of polymer electrolyte fuel cells (PEMFC).

Experimental Example 4: Analysis of cell characteristics of electrolyte membrane

Water absorption is an important membrane parameter that affects durability and proton conductivity. However, excessive moisture absorption can lead to membrane electrode assembly (MEA) failure due to the membrane dissolving in water.

Table 1 and Figure 8 show the results of analyzing the cell characteristics of the electrolyte membrane. According to this, the SIPiP membrane of Example 2 (59.39%) and the blended membrane of Example 3 (45.41%) exhibit higher water absorption than the SPiP membrane of Comparative Example 2 (43.51%) at 80°C. The SO ₂ of the sulfonamide group increases the delocalization of the negative charge, which promotes the interaction between the membrane and water molecules.

[Table 1]

This interaction also affects the expansion rate. The SIPiP membrane of Example 2 showed the greatest change in thickness and length (30.84%, 11.50%), the blending membrane of Example 3 showed the greatest change in thickness and length (21.33%, 11.20%), and the SPiP of Comparative Example 2 showed the greatest change in thickness and length (21.33%, 11.20%). The order of change was 19.65%, 11.37%).

This evidence also suggests the strong hydrophilic nature of the sulfone imide group. Ion exchange capacity (IEC) is highly dependent on water absorption, since water absorption plays a role in forming proton exchange channels. Accordingly, the SPiP of Comparative Example 2, the SIPiP of Example 2, and the blended membrane of Example 3 were titrated at 1.85 meq./g, 2.50 meq./g, and 2.20 meq./g, respectively, at 80°C. They all showed higher IEC than Nafion211® (0.91 meq./g) at 80 °C.

Experimental Example 5: Analysis of cell characteristics of electrolyte membrane

Figure 9 shows the results of measuring the proton conductivity of the membrane at a relative humidity of 90% and a temperature of 40 - 80°C, and Figure 10 shows the results of measurement at a relative humidity of 30 - 90% and a temperature of 80°C.

According to this, as is generally observed in most hydrocarbon electrolyte membranes, the proton conductivity of the membrane was found to steadily increase with an increase in temperature or relative humidity. Additionally, the proton conductivity of the membrane was consistent with the water absorption and ion exchange capacity (IEC) trends in the order of SIPiP > Blending > SPiP. The SIPiP membrane of Example 2 exhibited a very high proton conductivity of 97.46 mS/cm at 80°C and 90% relative humidity, a level similar to that of Nafion211® (101.22 mS/cm). Additionally, compared to other sulfonic hydrocarbon membranes with similar IEC and chemical structure, SIPiP of Example 2 showed the best membrane performance. In fact, the sulfone imide group of the membrane exhibits excellent hydrophilicity, resulting in high IEC, water absorption and proton conductivity. However, when the polymer chain is large, the interaction between the hydrophilic and hydrophobic regions is poor, which can lead to the formation of dead-end channels and narrow channels. Therefore, such a membrane may exhibit lower conductivity than Nafion211®.

Experimental Example 6: Stability analysis of electrolyte membrane

Figure 11 (a) shows the results of Fenton's reagent test for sulfonated polymer membrane and Nafion 211®. According to this, the chemical oxidation stability test of the membrane showed a weight loss in the presence of hot Fenton reagent for 8 hours, as shown in Figure 11 (a). Although the oxidation stability of the synthesized membrane was lower than that of Nafion 211®, the SIPiP membrane of Example 2 showed the highest chemical stability among the synthesized membranes. This stability is because the introduction of fluorine atoms into the polymer skeleton effectively improves the oxidation stability of the polymer exposed to highly oxidizing radical species.

Figure 11 (b) shows the results of measuring tensile stress and elongation break at a relative humidity of 50% and without water-swelling of the membrane. According to this, the tensile strength of the synthesized membrane was 20.2 ~ 42.8 MPa, which was higher than that of Nafion 211® (17.40 MPa). The tensile stress of the SIPiP membrane of Example 2 is lower than that of the SPiP membrane of Comparative Example 2, likely due to the higher expansion ratio of SIPiP compared to SPiP, which reflects the shorter strain rate during fabrication of the membrane electrode assembly (MEA). However, the elongation at break of the synthesized membrane is significantly lower than that of Nafion 211®, reflecting the short strain rate during the membrane electrolyte assembly process.

Experimental Example 7: Atomic force microscopy (AFM) image analysis

Figure 12 shows the results of atomic force microscopy (AFM) image analysis for (a) the SPiP film of Comparative Example 2, (b) the SIPiP film of Example 2, and (c) the blending film of Example 3, respectively.

According to this, each image shows a different surface pattern due to its different chemical structure. The bright and dark regions correspond to the hydrophobic and hydrophilic regions of the membrane, respectively. SIPiP (b) shows excellent separation of hydrophobic and hydrophilic regions and can therefore provide sufficient proton transport. In contrast, the separation of the SPiP membrane (a) of Comparative Example 2 and the blending membrane (c) of Example 3 was unclear and mixed, indicating that the conductivity was lower than that of SIPiP. Moreover, the similar properties of SPiP and blended membranes can be explained in similar fashion.

Experimental Example 8: Analysis of electrochemical properties of fuel cell

Figure 13 shows a membrane-electrode assembly (MEA) utilizing the SPiP membrane of Comparative Example 2, the SIPiP membrane of Example 2, the blended membrane of Example 3, and the Nafion 211® membrane measured at 70°C under fully humidified injection conditions. Polarization and open circuit voltage (OCV) curves for the fuel cell are shown.

According to this, the open circuit voltage (OCV) of all membrane electrode assemblies (MEA) is higher than 0.90 V, and the cell voltage decreases as the applied current increases, which means that all membranes have positive resistance to fuel gases of hydrogen and oxygen. It means indicating positive tolerance. The maximum power density was lower than that of Nafion 211® but was measured at 0.58, 0.49 and 0.52 W/cm ² for SIPiP, SPiP and blended membranes, respectively. It can be seen that the sulfone imide group of the SIPiP membrane of Example 2 increased the electrochemical properties of the hydrocarbon membrane.

According to the above-mentioned experimental examples, the main polymer precursor of PiP was synthesized from N-methyl isatin and biphenyl. In this process, two types of sulfonation were performed, and blended membranes were also prepared from SPiP and SIPiP through the melting method. The synthesis of monomers and polymers was investigated by 1H NMR and FT-IR. All polymers, including SPiP, SIPiP, and blended membranes, showed excellent thermal stability at temperatures below 170 °C, which basically meets the thermal requirements of PEMFC devices. Additionally, the SIPiP of the present invention exhibited very high ion exchange capacity (IEC) (2.56 meq./g at 80°C) and proton conductivity (97.46 mS/cm) comparable to Nafion211®. Additionally, due to the super gas-phase acidity of the sulfone imide group, the behavior of SIPiP was found to be better than that of the SPiP control during the entire measurement. Additionally, AFM analysis showed that defect channels formed in the hydrocarbon film reduce the proton conductivity compared to Nafion211®. Additionally, the SIPiP membrane of the present invention showed significantly improved single cell performance (0.58 W/cm ² ) at 100% relative humidity and 70°C when compared to Nafion 211®. Additionally, these results show that the SIPiP of the present invention is superior to SPiP as an alternative to the perfluorinated sulfonic acid (PFSA) membrane of polymer electrolyte fuel cells (PEMFC). Therefore, it appears that sulfone imide groups can be substitutes for sulfonic acids to improve fuel cell performance.

Although the embodiments of the present invention have been described above, those skilled in the art can add, change, delete or add components without departing from the spirit of the present invention as set forth in the patent claims. The present invention may be modified and changed in various ways, and this will also be included within the scope of rights of the present invention.

Claims (20)

A polymer for fuel cell electrolyte represented by structural formula 1 below; and
A polymer electrolyte membrane for fuel cells, which is a blending membrane containing poly(isatin-phenylene) to which a sulfonic acid group (-SO ₃ H) is bonded;
[Structural Formula 1]

In structural formula 1,
n is the number of repeat units,
R ¹ to R ³ are the same or different from each other, and each independently represents a hydrogen atom or a C1 to 20 alkyl group,
R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C20 chloroalkyl group, or a C1 to C20 fluoroalkyl group,
R ⁷ is a C1 to 20 alkyl group,
The compound represented by Structural Formula 1 has a weight average molecular weight (Mw) of 50,000 to 200,000. According to paragraph 1,
In structural formula 1,
n is the number of repeat units,
R ¹ to R ³ are the same or different from each other, and each independently represents a hydrogen atom or a C1 to 10 alkyl group,
R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C10 chloroalkyl group, or a C1 to C10 fluoroalkyl group,
R ⁷ is a polymer electrolyte membrane for a fuel cell, characterized in that it is a C1 to 10 alkyl group. According to paragraph 2,
In structural formula 1,
n is the number of repeat units,
R ¹ to R ³ are hydrogen atoms,
R ⁴ to R ⁶ are the same as or different from each other and are each independently a fluorine group,
R ⁷ is a polymer electrolyte membrane for a fuel cell, wherein is a methyl group. (a) preparing poly(isatine-phenylene) by reacting N-alkyl isatin and biphenyl in an organic solvent under a superacid catalyst;
(b) dissolving the polyisatin phenylene in an organic solvent and reacting it with chlorosulfonic acid to prepare sulfonated polyisatin phenylene;
(c) reacting the sulfonated polyisatin phenylene with thionyl chloride to produce chlorinated polyisatin phenylene; and
(d) reacting the chlorinated polyisatin phenylene with sulfamoyl halide to prepare a compound represented by the following structural formula 1.
[Structural Formula 1]

In structural formula 1,
n is the number of repeat units,
R ¹ to R ³ are the same or different from each other, and each independently represents a hydrogen atom or a C1 to 20 alkyl group,
R ⁴ to R ⁶ are the same as or different from each other, and are each independently a fluorine group, a chloro group, a C1 to C20 chloroalkyl group, or a C1 to C20 fluoroalkyl group,
R ⁷ is a C1 to 20 alkyl group,
The compound represented by Structural Formula 1 has a weight average molecular weight (Mw) of 50,000 to 200,000. According to paragraph 4,
In step (a),
A method for producing a polymer for fuel cell electrolyte, wherein the N-alkyl isatin is any one selected from N-methyl isatin, N-ethyl isatin, N-propyl isatin, and N-butyl isatin. According to paragraph 4,
In step (a),
The superacid catalyst is trifluoromethanesulfonic acid (TFSA), Fluorosulfuric acid, Trifluoromethanol, Carborane acid, and Chlorosulfonic acid. A method for producing a polymer for a fuel cell electrolyte, characterized in that it is selected from among acid) and fluoroboric acid. According to paragraph 4,
The N-alkyl isatin of step (a) is a method for producing a polymer for fuel cell electrolyte, characterized in that it is produced by reacting isatin with an alkyl halide in an organic solvent. According to paragraph 4,
The organic solvent is any one selected from dimethyl carbonate (DMC), dichloromethane (DCM), acetonitrile (ACN), trichloromethane (TCM), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC). Method for producing polymers for fuel cell electrolytes, characterized by: According to paragraph 4,
A method for producing a polymer for fuel cell electrolyte, characterized in that the reaction in step (b) is carried out at a temperature of 20 to 30 ° C. According to paragraph 4,
A method for producing a polymer for fuel cell electrolyte, wherein the reaction in step (b) is performed under an inert gas atmosphere. According to paragraph 4,
A method for producing a polymer for fuel cell electrolyte, characterized in that the reaction in step (c) is carried out at a temperature of 50 to 70 ° C. According to paragraph 4,
A method for producing a polymer for fuel cell electrolyte, wherein the reaction in step (c) is performed under an inert gas atmosphere. According to paragraph 4,
In step (d), the sulfamoyl halide is selected from sulfamoyl fluoride, sulfamoyl chloride, sulfamoyl bromide and sulfamoyl iodide. A method for producing a polymer for fuel cell electrolyte, characterized in that any one of the selected methods. According to paragraph 4,
A method for producing a polymer for fuel cell electrolyte, characterized in that the reaction in step (d) is carried out at a temperature of 20 to 30 ° C. delete delete delete A fuel cell comprising the polymer electrolyte membrane for fuel cells of claim 1. An electrical device comprising the fuel cell of claim 18. According to clause 19,
The electric device is any one selected from a communication device, a transportation device, an energy storage device, and an acoustic device.