KR100773322B1 - Polymer electrolyte membrane for fuel cell containing crosslinked PI and method for manufacturing same - Google Patents

Abstract

The present invention relates to a polymer electrolyte membrane comprising a PBI crosslinked with a polymer, a method for manufacturing the same, and a polymer electrolyte membrane fuel cell using the polymer electrolyte membrane. By using PBI crosslinked with a polymer as an electrolyte membrane, the size of PBI in the existing polymer electrolyte membrane can be reduced at high temperature. As a result, the performance reduction problem can be solved, and thus, when the polymer is used as a polymer electrolyte membrane, a high performance fuel cell can be manufactured.

Description

Polymer electrolyte membrane for fuel cell containing cross-liked PBI and method of preparing the same}

1 shows an I-V curve of a PBI crosslinked with a PBI.

The present invention relates to a polymer electrolyte membrane comprising a PBI crosslinked with a polymer, a method for manufacturing the same, and a polymer electrolyte membrane fuel cell using the polymer electrolyte membrane.

The fuel cell is a polymer electrolyte membrane fuel cell (PEMFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC) according to the type of electrolyte used, It may be classified into a solid oxide fuel cell (SOFC). Depending on the electrolyte used, the operating temperature of the fuel cell and the material of the components vary.

The basic structure of a PEMFC typically includes an anode (fuel electrode), a cathode (oxidant electrode), and a polymer electrolyte membrane disposed between the anode and the cathode. The anode of the PEMFC is provided with a catalyst layer for promoting the oxidation of the fuel, and the cathode of the PEMFC is provided with a catalyst layer for promoting the reduction of the oxidant.

As a fuel supplied to the anode of PEMFC, hydrogen, a hydrogen containing gas, mixed vapor of methanol and water, aqueous methanol solution, etc. are used normally. The oxidant supplied to the cathode of the PEMFC is typically oxygen, an oxygen containing gas or air. At the anode of the PEMFC, the fuel is oxidized to produce hydrogen ions and electrons. Hydrogen ions are transferred to the cathode through the electrolyte membrane, and electrons are transferred to the external circuit (load) through the conductor (or current collector). In the cathode of the PEMFC, water is generated by combining hydrogen ions transferred through the electrolyte membrane, electrons transferred from an external circuit through a conductor (or current collector), and oxygen. At this time, the movement of electrons via the anode, the external circuit and the cathode is power.

In PEMFC, the polymer electrolyte membrane not only functions as an ion conductor for the migration of hydrogen ions from the anode to the cathode, but also serves as a separator that blocks mechanical contact between the anode and the cathode. Therefore, the properties required for the polymer electrolyte membrane are excellent ion conductivity, electrochemical stability, high mechanical strength, thermal stability at operating temperature, ease of thinning and the like.

As the material of the polymer electrolyte membrane, a polymer electrolyte such as a sulfonate high fluorinated polymer having a main chain composed of a fluorinated alkylene and a side chain composed of a fluorinated vinyl ether having a sulfonic acid group at its terminal (for example, Nafion: Dupont's trademark) is used. The polymer electrolyte membrane exhibits excellent ion conductivity by impregnating an appropriate amount of water.

However, the electrolyte membrane is severely lowered in ionic conductivity due to moisture loss due to evaporation at an operating temperature of more than 100 ℃ to lose the function as an electrolyte membrane. Therefore, it is almost impossible to operate PEMFC using such a polymer electrolyte membrane under normal pressure and at a temperature of 100 ° C. or higher. In order to increase the operating temperature of the PEMFC to more than 100 ℃, a method of mounting a humidifier to the PEMFC or operating the PEMFC under pressurized conditions, a method of using a polymer electrolyte that does not require humidification has been proposed. However, applying a pressurized system or mounting a humidifier not only greatly increases the size and weight of the PEMFC, but also reduces the overall efficiency of the power generation system.

It is a "humidification-free polymer electrolyte membrane" that exhibits excellent ionic conductivity without humidification, which can maximize the application range of PEMFC, and materials such as polybenzoimidazole (PBI), sulfuric acid or phosphoric acid-doped polybenzoimidazole Is disclosed. However, when the PBI-based electrolyte membrane is used as the polymer electrolyte membrane at a temperature of 100 ° C. to 200 ° C., the thermal and chemical stability at high temperatures are excellent, but the polymer material is reduced in the long term, resulting in a decrease in performance in the long term.

In order to solve the above problems, an object of the present invention is to provide a polymer electrolyte membrane in which dimensional instability of PBI is solved by crosslinking an existing inorganic acid-doped PBI with a polymer. It is also an object of the present invention to provide a fuel cell comprising the polymer electrolyte membrane.

In order to achieve the above object, the present invention provides a polymer A represented by the following formula (1).

(X is SO ₂ or CO; Y is C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , CH ₂ or no atom;

n / m = 1/99 to 50/50, n + m = 500 to 10,000)

In addition, the present invention is a polymer A represented by the formula (1); And a product obtained by crosslinking polybenzoimidazole (PBI) or poly (2,5-benzimidazole) (ABPBI).

In the polymer electrolyte membrane of the present invention, an inorganic acid is further included, and the inorganic acid is at least one selected from phosphoric acid, nitric acid, hydrochloric acid, and sulfuric acid. In addition, the weight ratio of the polymer A: PBI or the polymer A: ABPBI to the reaction is characterized in that 1:10 ~ 10: 1.

The present invention comprises the steps of mixing the polymer A, represented by the formula (1), and PBI or ABPBI dissolved in a solvent (S1); Casting the membrane with the mixture (S2); And it provides a polymer electrolyte membrane manufacturing method comprising the step (S3) of irradiating and drying the membrane UV.

In the manufacturing method of the polymer electrolyte membrane of the present invention, the method further comprises the step of immersing the membrane dried in the step S3 in the inorganic acid and the inorganic acid is at least one selected from phosphoric acid, nitric acid, hydrochloric acid and sulfuric acid. It is characterized by. In addition, the step S1 is characterized in that the polymer A and PBI, or polymer A and ABPBI are mixed in a weight ratio of 1:10 to 10: 1.

In addition, the present invention is the polymer electrolyte membrane; Cathode; And it provides a polymer electrolyte membrane fuel cell comprising an anode.

Hereinafter, the present invention will be described in more detail.

In the polymer A represented by Formula 1, the sum of n and m is different depending on the sophistication of the synthesis method, but 500 to 10,000 is preferable, and n / m is preferably 1/99 to 50/50. This is because when the size is less than 1/99, the crosslink is small, and when the size is larger than 50/50, the crosslink is too large to easily break the polymer membrane.

In order to prepare polymer A, wherein X is SO ₂ in the polymer A represented by Formula 1, polymer A represented by Formula 1 is prepared from synthesis of polyethersulfone instead of polyether ketone (PEK).

It is possible to use ABPBI (poly (2,5-benzimidazole) represented by Formula 2 below instead of PBI as a compound crosslinked with the polymer A represented by Formula 1 above.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following embodiments are intended to illustrate the invention and are not intended to limit the invention.

Example 1 Polyetherketone (PEK) Synthesis

Difluorobenzophenone (4.364 g, 20 mmol), 4-methyl hydroquione (1.2414 g, 10 mmol), Bisphenol A (2.2829 g) in a 100 mL round bottom flask , 10 mmol), potassium carbonate (5.5284 g, 40 mmol), DMAc (Dimethylacetamide) (20 mL) and toluene (20 mL) were added and heated by a Deanstark trap device under a nitrogen atmosphere for 4 hours. . Toluene and water in the flask were then removed via a Deanstock trap at 1 hour intervals and the flask was heated with stirring at 180 ° C. for 20 hours. After the reaction was completed, the flask was cooled to room temperature, 20 mL of NMP was added to the polymer mixture having increased viscosity to completely dissolve it, and then put into 1 L of methanol to obtain a white precipitate. The white solid was dried in a vacuum oven at 60 ° C. for 2 hours, the remaining inorganic material and unreacted material were removed using a Soxhlet apparatus, and then the obtained solid was dried at 60 ° C. in a vacuum oven for 24 hours. PEK (Material 1 of Scheme 1) was obtained.

¹ H NMR (500 MHz, CDCl _3, δ ) 9.5-9.2 (8H, broad signal, Ar H ), 7.9-7.7 (8H, broad siganl, Ar H ), 7.1-6.8 (11H, broad signal, ArH) 2.3 -2.1 (3H, broad signal, ArC H ₃ ) 1.8-1.6 (6H, broad signal, 2 x ArC H ₃ from bisphenol A)

Example 2: Bromination of PEK

PEK (5 g) prepared in Example 1 was dissolved in methylene chloride (50 mL) in a round bottom flask. When the polymer was dissolved in a solvent, a mixture of CCl ₄ (100 ml) and DCM (50 ml) was added and N-bromosuccinimide (NBS) (1.88 g) was added thereto, followed by UV irradiation for 10 minutes. Then, the yellow liquid obtained by stirring the solution at room temperature under nitrogen for 24 hours was added to 1 L of methanol to precipitate a precipitate, and the precipitate was put in water again after the filter and stirred and filtered. The obtained solid was dried in a vacuum oven for 24 hours to obtain a PEK copolymer bromide (Material 2 of Scheme 2).

¹ H NMR (500 MHz, CDCl _3, δ ) 8.6-8.3 (8H, broad signal, Ar H ), 7.9-7.7 (8H, broad signal, Ar H ), 7.1-6.8 (11H, broad signal, ArH), 4.5-4.4 (2H, broad signal, ArC H ₂ Br), 1.8-1.6 (6H, broad signal, 2 × ArC H ₃ from bisphenol A).

Example 3 Substitution of Benzyl Bromide

PEK copolymer bromide (3 g) prepared in Scheme 2 was dissolved in DMF (50 mL), NaN ₃ (0.37 g) was added thereto, and the mixture was stirred at room temperature and nitrogen for 24 hours. After the reaction was completed, the obtained liquid was poured into 500 mL of methanol to precipitate crystals, filtered, and the solid was put back into 1 L of distilled water and washed. The obtained solid was again dried in a vacuum oven for 24 hours to obtain Polymer A (Material 3 of Scheme 3).

ν _max (KBr) / cm ^-1 3432 (vinyl CH), 3094 (CH), 3056 (CH), 2094 (N ₃ ), 1652 (C = O), 1601 (vinyl C = C), 1491 and 1232

Example 4: PBI Synthesis

In a 1 L round flask, 3.3'-Diaminobenzidine (12g) and isophthalic acid (9.3g) were put in polyphosphoric acid (PPA) and heated at 220 ° C in a nitrogen atmosphere. To 25 hours. Stirring was used with a mechanical overhead stirrer. When the stirring speed was adjusted to 100 RPM at room temperature, the viscosity of the PPA decreased with increasing temperature and increased to 300 RPM, and as the reaction proceeded, the viscosity of the solution increased to finally 180 to 200 RPM. The color of the solution also changed from ocher to dark brown as the reaction proceeded. The solution thus prepared was precipitated in water to obtain a polymer, and the polymer was dried in a vacuum oven at 100 ° C. for 24 hours to obtain PBI powder having an intrinsic viscosity of about 1.5 to 3.0 dL / g.

Example 5: Crosslinked PBI Film Preparation

PBI (5 g) prepared in Example 4 and Polymer A (2 g) prepared in Example 3 were dissolved in DMAc (100 mL), poured into an appropriate amount on a glass plate, and the membrane was cast using a doctor blade (PBI). : Polymer A = 1: 10 ~ 10: 1). The polymer solution membrane was irradiated with UV for 10 minutes and dried in a vacuum oven at 60 ° C. for 50 hours to prepare a crosslinked PBI membrane. The prepared membrane was immersed in 60% phosphoric acid for 3 days to obtain a polymer electrolyte membrane doped with 400%.

Comparative Example: Existing PBI Film

PBI (5 g) was dissolved in DMAc (100 mL), an appropriate amount was poured on a glass plate, and the membrane was cast with a doctor blade. This was dried for 50 hours in a 60 ℃ vacuum oven to prepare a PBI film. The prepared membrane was immersed in 60% phosphoric acid for 3 days to obtain a polymer electrolyte membrane doped with 400%.

Experimental Example: Unit Battery Performance Test

The fuel cell was fabricated without hot press operation by mounting electrodes on the crosslinked PBI membrane prepared in Example 5 and the PBI membrane prepared in Comparative Example, and the performance of the unit cell was tested (condition 150 ° C., hydrogen / air). .

As a result, as shown in FIG. 1, which is an I-V curve, it was found that the unit cell performance of the battery having the crosslinked PBI film of Example 5 was higher than that of the comparative example.

As described above, by using the PBI crosslinked with the polymer as an electrolyte membrane, it is possible to solve the problem that the size of the PBI is reduced at a high temperature in the conventional polymer electrolyte membrane. As a result, the performance reduction problem can be solved, and thus, when the polymer is used as a polymer electrolyte membrane, a high performance fuel cell can be manufactured.

Claims (10)

Polymer A represented by Formula 1 below. [Formula 1]

(X is SO ₂ or CO; Y is C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , CH ₂ or no atom; n / m = 1/99 to 50/50, n + m = 500 to 10,000) Polymer A represented by the following Formula 1; And A polymer electrolyte membrane comprising a product obtained by crosslinking polybenzoimidazole (PBI) or poly (2,5-benzimidazole) (ABPBI). [Formula 1]

(X is SO ₂ or CO; Y is C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , CH ₂ or no atom; n / m = 1/99 to 50/50, n + m = 500 to 10,000) The polymer electrolyte membrane of Claim 2, further comprising an inorganic acid. The polymer electrolyte membrane according to claim 2 or 3, wherein the weight ratio of the polymer A: PBI to react or the weight ratio of the polymer A: ABPBI is 1:10 to 10: 1. The polymer electrolyte membrane of Claim 3, wherein the inorganic acid is at least one selected from phosphoric acid, nitric acid, hydrochloric acid, and sulfuric acid. Mixing the polymer A represented by Formula 1 with PBI or ABPBI and dissolving it in a solvent (S1); Casting the membrane with the mixture (S2); And The polymer electrolyte membrane manufacturing method comprising the step of irradiating and drying the membrane UV (S3). [Formula 1]

(X is SO ₂ or CO; Y is C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , CH ₂ or no atom; n / m = 1/99 to 50/50, n + m = 500 to 10,000) The method according to claim 6, wherein the manufacturing method further comprises the step of doping the membrane dried in the step S3 in an inorganic acid. The method of claim 6 or 7, wherein the step S1 comprises polymer A and PBI, or polymer A and ABPBI in a weight ratio of 1:10 to 10: 1. The method of claim 7, wherein the inorganic acid is at least one selected from phosphoric acid, nitric acid, hydrochloric acid, and sulfuric acid. The polymer electrolyte membrane according to claim 2 or 3; Cathode; And A polymer electrolyte membrane fuel cell comprising an anode.

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