KR20140021281A - Novel hyper branched polymer, electrolyte containing thereof for fuel cell, method for preparing the same and fuel cell containing the electrolyte - Google Patents

Abstract

The present invention relates to a novel hyperbranched polymer with a hyperbranched structure in which ends of each monomer are connected to each other. The novel hyperbranched polymer has a high impregnation rate of phosphoric acid in a fuel cell and a high maintanance rate of the impregnated phosphoric acid, and has high thermal/mechanical stability after using long-term use. A user can use a polymer electrolyte membrane including the novel hyperbranched polymer and the fuel cell including the membrane, and power generation efficiency is remarkably improved. [Reference numerals] (AA) Chemical shift

Description

Novel hyper branched polymer, electrolyte containing etc for fuel cell, method for preparing the same and fuel cell containing the electrolyte}

The present invention relates to a novel hyperbranched polymer, and more particularly, a novel hyperbranched polymer having a high phosphoric acid impregnation amount and a high retention rate in a high temperature polymer fuel cell, a polymer electrolyte membrane for a fuel cell including the same, and a The present invention relates to a manufacturing method and a fuel cell including the membrane.

Recently, due to environmental problems and energy depletion, interest in new energy to replace oil is increasing. One of the means that is attracting attention as such alternative energy is a fuel cell using hydrogen or hydrocarbon gas. A fuel cell is a new power generation system that directly converts energy generated by electrochemical reaction between fuel gas and oxidant gas into electrical energy. Research is being actively conducted to develop fuel cells with higher energy efficiency and high reliability.

The types of fuel cells are divided according to the characteristics of the configuration and the operating environment. Typically, molten carbonate fuel cells (MCFCs), alkaline fuel cells (AFCs) and solid oxide fuel cells (Solid) Oxide Fuel Cell (SOFC), Direct Methanol Fuel Cell (DMFC), Direct Ethanol Fuel Cell (DEFC) and Polymer electrolyte membrane fuel cell (PEMFC).

Among them, the polymer electrolyte membrane fuel cell (PEMFC) has a simpler structure than other fuel cells, has a quick start, quick response and excellent durability. In addition to hydrogen, methanol or natural gas can be used as fuel The development of electric power sources for automobiles, power generation facilities for distributed local installations, military power sources, spacecraft power sources and household electric power are being developed.

The development mechanism of this PEMFC is as follows. In the anode, hydrogen as a reactor is supplied to oxidize the hydrogen molecules, which are separated into hydrogen ions and electrons. The generated hydrogen ions are transferred to the cathode through the polymer electrolyte membrane. At the cathode, a reduction reaction occurs, And the oxygen ions are converted into water molecules by reacting with the hydrogen ions migrating from the anode. Through such a series of reactions, a potential difference occurs between the anode and the cathode, and power generation is performed from this potential difference. This series of reactions is outlined below:

^{_{Anode: H 2 → 2H + + 2e}} -

^{_{Cathode: 1/2 O 2 + 2H + +}} 2e - → H 2 O

Overall Battery Reaction: H ₂ + 1/2 O ₂ → H ₂ O

In the development mechanism of PEMFC, the proton conductivity of the polymer electrolyte membrane is equal to the charge transfer force of the battery, which is also a key factor directly related to the generation efficiency. To this end, many PEMFCs developed to date use a perfluoro-silfonic acid (PFSA) polymer electrolyte membrane, and Nafion® from Dupont, USA, is widely used. However, since PFSA-based polymer electrolyte membranes basically have a proton conduction mechanism that depends on water, an additional temperature maintenance device should be introduced to limit the operating temperature to less than the boiling point of water. Carbon cannot be removed by complete reaction, thus producing carbon monoxide, a product of carbon incomplete reaction, and the produced carbon monoxide gradually accumulates in the PEMFC's platinum catalyst with strong adsorptive power, and the carbon monoxide-adsorbed platinum catalyst is incapable of operating. There is a problem that significantly lowered as a result, the efficiency of the PEMFC power generation is sharply lowered. This problem of PFSA-based PEMFC, also called low temperature PEMFC, has emerged as a top priority to overcome for practical use.

As one of attempts to overcome the problem of the low temperature PEMFC, development of a high temperature PEMFC using a polymidazole-based electrolyte membrane has been actively made. Since the polyimidazole-based electrolyte membrane has a Grotus mechanism through phosphoric acid, which does not depend on water, it can set an operating environment of more than 100 ° C. so that it does not show the carbon monoxide poisoning phenomenon of the platinum catalyst inherent in low temperature type PEMFC. The advantage is that no additional device is required for maintaining a low temperature environment. As a result, high temperature PEMFCs are more likely to be developed as devices with increased power generation efficiency than low temperature PEMFCs.

However, as a limitation of the high temperature type PEMFC, it is technically difficult to impregnate the polymer electrolyte membrane with a large amount of phosphoric acid, which is essential for proton conduction, and even if a technique for impregnating such a large amount of phosphoric acid is developed, its retention rate is not high, so the proton conductivity with time The loss of is large, there is a problem that gradually decreases the efficiency of power generation. Therefore, there is a further demand for the development of a high temperature polymer electrolyte membrane having a high retention rate for impregnation with a large amount of phosphoric acid.

Accordingly, the first problem to be solved by the present invention is a novel hyperbranched polymer having a high impregnation amount of phosphoric acid in the fuel cell polymer electrolyte membrane, high retention thereof, and excellent thermal / mechanical stability even for long-term use. To provide.

The second problem to be solved by the present invention is to provide a polymer electrolyte membrane comprising the novel hyper branched polymer.

A third object of the present invention is to provide a fuel cell including the polymer electrolyte membrane.

A fourth object of the present invention is to provide a novel hyperbranched polymer, a polymer electrolyte membrane including the same, and a method of manufacturing a fuel cell including the membrane.

In order to solve the first problem,

It is represented by the following [Formula 1], the terminal of each unit is connected to provide a hyper branched (hyper branched) polymer characterized in that it has a net structure.

[Formula 1]

In the above formula (1)

N is an integer of 50 to 10000.

According to one embodiment of the present invention, the unit of [Formula 1] may be prepared using a compound represented by the following [Formula 2] and 3,3'-diaminobenzidine.

(2)

According to another embodiment of the present invention, the compound represented by [Formula 2] may be prepared using trimellitic anhydride and 3,3'-diaminobenzidine.

In order to solve the second problem,

It provides a polymer electrolyte membrane comprising the hyper branched (hyper branched) polymer.

The present invention provides a fuel cell including the polymer electrolyte membrane in order to solve the third problem.

The present invention to solve the fourth problem,

(a) synthesizing a hyper branched polymer having a structure represented by the following [Formula 1]; And

It provides a method for producing a polymer electrolyte membrane comprising (b) immersing the synthesized polymer in an acidic solution.

[Formula 1]

According to an embodiment of the present invention,

Step (a) may be characterized by including the following steps.

(Iii) dissolving trimellitic anhydride and 3,3'-diaminobenzidine in dimethylformamide, followed by stirring to obtain a compound represented by the following [Formula 2]; And

(Ii) dissolving the compound of [Formula 2] and 3,3′-diaminobenzidine obtained in polyphosphoric acid, followed by reaction to obtain a polymer of [Formula 1].

(2)

According to another embodiment of the present invention,

After the reaction of step (ii), water may be added to precipitate the product and neutralize with potassium hydroxide.

According to another embodiment of the present invention,

The acidic solution of step (b) may be a phosphoric acid solution or a phosphomolybdic acid solution.

According to another embodiment of the present invention,

In step (b), the polymer may be dipped in an acidic solution for 3-50 hours.

As described above, according to the present invention, a novel hyperbranched polymer having a high phosphoric acid impregnation rate, a high retention rate of impregnated phosphoric acid, and high thermal / mechanical stability even for long-term use, a polymer electrolyte comprising the same The membrane and the fuel cell including the membrane can be used, and thus the power generation efficiency is remarkably improved.

1 is a graph showing proton conductivity of a fuel cell electrolyte membrane and a comparative example according to a preferred embodiment of the present invention measured over time.
2 is a result of H-1 NMR analysis of a single molecule according to the preparation of the present invention.
3 is a C-13 NMR analysis result of a polymer for a fuel cell according to a monomolecular and a preferred embodiment according to the preparation example of the present invention.
4 is a graph illustrating thermogravimetric analysis (TGA) of a polymer for fuel cells, an electrolyte membrane, and a comparative example according to an exemplary embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention is represented by the following [Formula 1], the terminal of each unit is connected to provide a hyper branched (hyper branched) polymer characterized in that it has a net structure.

[Formula 1]

In the above formula (1)

N is an integer of 50 to 10000.

As a preferred embodiment of the present invention, for example, a polymer as shown in [Formula 3] can be prepared.

(3)

The polymer according to the preferred embodiment of the present invention represented by [Formula 1] or [Formula 3] forms a stable covalent bond structure and is thermally / mechanically stable for a long time, and has affinity for phosphoric acid by including abundant benzimidazole functional groups. This is high.

The polymer of [Formula 1] according to the present invention may be prepared as shown in [Scheme 1] using a diterephthalic acid compound represented by the following [Formula 2] and 3,3′-diaminobenzidine.

(2)

[Reaction Scheme 1]

In addition, the compound represented by [Formula 2] may be prepared as shown in [Scheme 2] using trimellitic anhydride and 3,3'-diaminobenzidine. However, the present invention is not limited to these raw materials, and those skilled in the art may easily select other raw materials to implement or reproduce the present invention.

[Reaction Scheme 2]

The compound of [Formula 2] may be characterized in that the diterephthalic acid compound group is bonded to the terminal for the purpose of crosslinking the polymer. The benzimidazole functional group located at the center part and having a binding property to phosphoric acid are also included in the structural features of the compound of [Formula 2].

By impregnating a hyper branched polymer according to the present invention to phosphoric acid, a polymer electrolyte membrane according to a preferred embodiment of the present invention can be implemented. In this case, the phosphoric acid impregnated in the membrane acts as a proton conduction media, and the polymer electrolyte membrane according to the present invention has a high phosphoric acid impregnation due to the high phosphoric acid affinity of the polymer unit, so that the proton conductance is excellent, and the retention force therefor. Is also excellent. In addition, by including the polymer electrolyte membrane, it is possible to use a fuel cell having a high proton conductivity and excellent retention thereof, and having a markedly improved power generation efficiency.

The method for preparing a polymer electrolyte membrane according to the present invention comprises the steps of synthesizing the compound of [Chemical Formula 2], polymerizing the synthesized compound of [Chemical Formula 2] to synthesize a hyper branched (hyper branched) polymer of [Chemical Formula 1] step; And immersing the polymer in an acidic solution. Synthesis of the compound of [Formula 2] and the polymer of [Formula 1] may be performed at the same time, but after completing the synthesis of the compound of [Formula 2] first to prepare an additive for preparing an electrolyte membrane, and then polymerized by It may be a stepwise process for forming the polymer of 1].

More specifically, the manufacturing method of the polymer electrolyte membrane according to the present invention,

(a) synthesizing a hyper branched polymer having a structure represented by the following [Formula 1]; And

(b) immersing the synthesized polymer in an acidic solution.

[Formula 1]

In addition, step (a) may include the following steps:

(Iii) dissolving trimellitic anhydride and 3,3'-diaminobenzidine in dimethylformamide as an organic solvent, followed by stirring to obtain a compound represented by the following [Formula 2]; And

(Ii) dissolving the obtained compound of Chemical Formula 2 and 3,3'-diaminobenzidine in polyphosphoric acid, followed by reaction to obtain the polymer of Chemical Formula 1;

(2)

After the reaction of step (ii), it may further comprise the step of adding water to precipitate the product, neutralizing with potassium hydroxide.

In the acidic solution of step (b), preferably, a phosphoric acid solution may be used, but another acidic aqueous solution including phosphorus may be used, for example, a phosphomolybdic acid solution may be used.

In addition, the immersion step of (b) is preferably made for 3 hours to 50 hours, which is less than 3 hours does not show a sufficient proton conductivity due to insufficient impregnation of phosphoric acid, after 50 hours according to the present invention This is because the increase in the impregnation amount of the polymer electrolyte membrane is stopped.

Hereinafter, the present invention will be described in more detail with reference to the drawings, preparation examples, examples, test examples, and comparative examples. However, the following is intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereto.

Manufacturing example  For polymer synthesis Monomolecular  Produce

[Scheme 2] shows a schematic process of monomolecular synthesis as a preferred embodiment of the present invention. 1.921 g (0.01 mol) of (A) trimellitic anhydride and (B) 4.285 g (0.02 mol) of 3,3'-diaminobenzidine were added to dimethylformamide. After dissolving each in 20 mL of (dimethyl formamide), two solutions were added to a 250 mL Erlenmeyer flask and stirred under a reflux system. Stirring was carried out for 1 hour at room temperature and 12 hours in a heating environment. After the reaction was completed, the mixture was cooled to room temperature again, and the obtained yellow powder was filtered and dried in a vacuum oven for 24 hours. The compound represented by [Formula 2] was obtained. 2 shows the results of H-1 NMR analysis of the single molecule. Through this, the molecular structure can be confirmed by specifying the hydrogen atom bonded in the single molecule.

[Reaction Scheme 2]

(2)

Example  : Polymers and Polymers Electrolyte membrane  Produce

[Scheme 1] shows a schematic process of the synthesis of a hyper branched (hyper branched) as an embodiment of the present invention. (A) 1.125 g (0.002 mol) of the monomolecule represented by the above [Formula 2] and (B) 0.865 g (3,3'-diaminobenzidine) (B) 0.004 mol) was dissolved in 180 g of polyphosphoric acid. Next, the reaction was performed for 24 hours while maintaining the temperature at 230 ° C to 240 ° C in a nitrogen atmosphere and a reflux apparatus. After the reaction was completed, the product was precipitated with water and neutralized with potassium hydroxide (KOH) until pH was 7. The product was washed several times with boiling water, then filtered and dried in a vacuum oven for 24 hours to give a powder. The powder was dissolved in methanesulfonic acid and cast in the form of a membrane, and then cured in an oven at 80 ° C. for 1 hour, at 100 ° C. for 1 hour, and at 160 ° C. for 2 hours and 30 minutes. A polymer according to one preferred embodiment was prepared in the form of a membrane. Two carboxylic acid functional groups at both ends of a terephthalic acid compound bonded to both ends of a single molecule cause a general radical polymerization reaction with terminal amine groups of 3,3'-diaminobenzidine, and also a number of benzimidazole functions through chain polymerization. It appears to form a group. Thereafter, the polymer membrane cast in the form of a membrane was immersed in phosphoric acid and processed into a final form of the polymer electrolyte membrane for a fuel cell.

3 shows the results of C-13 NMR analysis for the single molecule of [Formula 2] and the polymer represented by the following [Formula 1] according to the preparation example, and the single molecule (a) and the polymerized fuel cell polymer ( The molecular structure can be confirmed by specifying the carbon atoms in b).

[Reaction Scheme 1]

[Formula 1]

Comparative Example  m- PBI  Polymer and Polymer Using the Same Electrolyte membrane  Produce

3.235 g (15.1 mmol) of 3,3'-diaminobenzidine and 2.509 g (15.1 mmol) of isophthalic acid were dissolved in 160 g of polyphosphoric acid. Next, the mixture was heated to a temperature of 220 ° C. under a nitrogen atmosphere and a reflux apparatus, and reacted for 30 hours. After the reaction was completed, the product was precipitated with water and neutralized with potassium hydroxide (KOH) until pH was 7. The product was washed several times with boiling water, then filtered and dried in a vacuum oven for 24 hours. The powder thus obtained was dissolved in methanesulfonic acid to cast a membrane, and then cured in an oven at 80 ° C. for 1 hour, at 100 ° C. for 1 hour, and at 160 ° C. for 2 hours 30 minutes, and then m-PBI. A membrane was prepared, which was immersed in phosphoric acid, and processed into the final form of the polymer electrolyte membrane for fuel cells.

Test Example  1: Measurement of Proton Conductivity

The efficiency of a fuel cell can be expressed as an output voltage that depends on the fuel cell charge density. Since the charge density of PEMFC depends on the proton conductivity of the electrolyte, the higher the proton conductivity of the polymer electrolyte membrane of PEMFC is, the better.

Proton conductivity can be measured using electrochemical impedance spectroscopy techniques in the frequency range of 100 kHz to 10 Hz. The resistance of the polymer electrolyte membrane according to the present invention was measured using an Autolab impedance analyzer and a proton conductivity cell at a temperature of 150 ° C. Proton conductivity σ is determined from Equation 1 below.

[Equation 1]

In the above formula, D, l _s , w _s , and R represent the distance of the electrode, the thickness of the electrolyte membrane, the width of the electrolyte membrane, and the resistance of the polymer electrolyte membrane, respectively.

Table 1 is a result of measuring the proton conductivity (Proton conductivity) of the polymer electrolyte membrane according to the Comparative Examples and Examples with time, Figure 1 is a graph showing the results of Table 1, (a) is a comparative example , (b) shows the change in proton conductivity with time for the example.

Time (hr)
Proton Conductivity (S / cm) (a) (b) One 0.0732 0.289 5 0.0533 0.227 10 0.0513 0.207 20 0.0521 0.197 50 0.0497 0.175 70 0.0495 0.173 80 0.0496 0.173

In Table 1 and Figure 1, it can be seen that the proton conductivity decreases with time. (a) The m-PBI polymer electrolyte membrane had a prominent decrease in proton conductivity after 70 hours, compared to the initial stage. (b) The polymer electrolyte membrane according to the embodiment of the present invention exhibited not only a high initial proton conductivity but also a lapse of time. The reduction rate is also low.

These results seem to be due to the significantly low leakage rate of phosphoric acid directly connected to the proton conductivity in the polymer electrolyte membrane according to an embodiment of the present invention. In addition, the fact that this test example was made at a high temperature of 150 ℃ suggests that the polymer electrolyte membrane according to the present invention is thermally stable.

Test Example  2: thermogravimetric analysis Thermogravimetric analysis )

In order to confirm the life and stability of the polymer electrolyte membrane according to the present invention, a thermogravimetric analysis was performed to measure the mass change in an environment of heating up to 800 ° C. from room temperature.

Figure 4 is (a) hyper-branched polymer powder according to an embodiment of the present invention, (b) m-PBI polymer powder, (c) the polymer electrolyte membrane according to the present invention before immersed in phosphoric acid, (d) phosphoric acid The thermogravimetric analysis results of the m-PBI polymer electrolyte membrane before immersion, the polymer electrolyte membrane according to the present invention (e) immersed in phosphoric acid, and (f) the m-PBI polymer electrolyte membrane immersed in phosphoric acid are shown.

Referring to this, the polymer and the polymer electrolyte membrane according to the present invention are similar or superior in terms of thermal stability than m-PBI. Exceptionally, when comparing (e) and (f), the (e) line is relatively low because the amount of phosphoric acid immersion in the polymer electrolyte membrane according to the present invention is relatively high, and the amount of phosphoric acid pyrolyzed around 150 ° C is also large. In conclusion, according to the present invention, it is possible to secure sufficient phosphoric acid immersion amount with thermal stability in PEMFC operated at a high temperature of 100 ° C. or more for a long time.

Test Example  3: universal testing machine ( universal testing machine Property evaluation using

UTM is a tester that checks the mechanical strength. The UTM is composed of a test device load device and a load metering device for tensile test, compression test and bending test. Among the mechanical strengths of the polymer electrolyte membrane according to the present invention, in particular, physical property evaluation using UTM was carried out to investigate tensile strength.

In Table 2 (a) is a case of the m-PBI polymer electrolyte membrane as a comparative example, (b) is a case of the polymer electrolyte membrane according to an embodiment of the present invention, than the m-PBI polymer electrolyte membrane of the polymer electrolyte membrane according to the present invention Mechanical strength is better.

Tensile Stress (MPa) Elongation at break (%) Density (g / cm ² ) Tensile Stress / Density (a) 80.5 20.2 1.51 53.3 (b) 75.2 6.22 1.28 58.8

Claims (10)

A hyper branched polymer represented by the following [Formula 1], wherein the terminals of each unit are connected to have a net structure.
[Chemical Formula 1]

In [Formula 1],
N is an integer of 50 to 10000. The method of claim 1,
The unit of [Formula 1] is a hyper branched (hyper branched) polymer, characterized in that prepared using the compound represented by the formula [2] and 3,3'-diaminobenzidine.
(2)

3. The method of claim 2,
The compound represented by [Formula 2] is a hyper branched (hyper branched) polymer, characterized in that prepared using trimellitic anhydride and 3,3'-diaminobenzidine. A polymer electrolyte membrane comprising the hyper branched polymer according to any one of claims 1 to 3. A fuel cell comprising the polymer electrolyte membrane according to claim 4. (a) synthesizing a hyper branched polymer having a structure represented by the following [Formula 1]; And
(b) immersing the synthesized polymer in an acidic solution.
[Chemical Formula 1]

The method according to claim 6,
The step (a) is a method for producing a polymer electrolyte membrane, characterized in that it comprises the following steps.
(Iii) dissolving trimellitic anhydride and 3,3'-diaminobenzidine in dimethylformamide, followed by stirring to obtain a compound represented by the following [Formula 2]; And
(Ii) dissolving the compound of [Formula 2] and 3,3′-diaminobenzidine obtained in polyphosphoric acid, followed by reaction to obtain a polymer of [Formula 1].
(2)

The method of claim 7, wherein
After the reaction of step (ii), the method of producing a polymer electrolyte membrane, further comprising the step of adding water to precipitate the product, and neutralized with potassium hydroxide. The method according to claim 6,
The acidic solution of step (b) is a method of producing a polymer electrolyte membrane, characterized in that the phosphoric acid solution or phosphomolybdic acid solution. The method according to claim 6,
Method of producing a polymer electrolyte membrane, characterized in that in the step (b) the polymer is immersed in an acidic solution for 3-50 hours.

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