KR100681770B1 - Polybenzimidazole catalyst binder, method for preparing the same, membrane electrode assembly using the polybenzimidazole catalyst binder - Google Patents

Abstract

The present invention provides a catalyst binder which is a catalyst binder used in the preparation of an electrode of a MEA including a membrane prepared using a polybenzimidazole compound, and comprises polybenzimidazole. In addition, the pole Revenge imidazole is 3,3 ^'- diaminodiphenyl benzimidazolyl dynes (3, ^3' of the monomers -Diaminobenzidine) and isophthalic acid (isophthalic acid) or terephthalic acid (terephthalic acid), a poly phosphoric acid (polyphosphoric acid) or P ₂ O ₅ and a mixture of any one or two of CF ₃ SO ₃ H or CH ₃ SO ₃ H and a polymer prepared by reacting by heating, the polybenzimidazole is More preferably, the mixture is a mixture of both CF ₃ SO ₃ H and CH ₃ SO ₃ H, and the mixture is most preferably 1: 1 in volume ratio of CF ₃ SO ₃ H and CH ₃ SO ₃ H. Do.

 According to the present invention, unlike the low performance Nafion type perfluorosulfonic acid polymer that has been conventionally used, it is possible to operate a fuel cell in a high temperature and low humidity state. In addition, according to the present invention, polybenzimidazole for a catalyst binder which is soluble in organic and inorganic solvents and has a sufficient high molecular weight suitable for a catalyst binder can be obtained.

Nafion, polybenzimidazole, membrane, catalyst binder, electrode, membrane electrode assembly

Description

Polybenzimidazole catalyst binder, method for preparing the same, and membrane electrode assembly using the same {polybenzimidazole catalyst binder, method for preparing the same, membrane electrode assembly using the polybenzimidazole catalyst binder}

1 is a view showing a chemical reaction formula for preparing a PBI in an embodiment of the present invention.

FIG. 2 is a graph showing the influence of operating temperature on single fuel cell efficiency including ABPBI MEA using PBI as a catalyst binder in an embodiment of the present invention.

FIG. 3 is a graph showing polarities at different fuel injections of ABPBI MEAs using PBI as a catalyst binder in Examples of the present invention.

4 is a graph showing a polar curve of ABPBI MEA using Nafion as a catalyst binder in Comparative Example of the present invention.

The present invention relates to a polybenzimidazole catalyst binder, a preparation method thereof and a membrane electrode assembly using the same.

MEA (Membrane Electrode Assembly) is the most important part of the fuel cell, and conventionally, Nafion type perfluorosulfonic acid polymer is used as the membrane and catalyst binder of MEA.

However, since the Nafion type polymer easily dries in a high temperature and low humidity state, it is not suitable when the fuel cell is operated in a high temperature and low humidity state.

Meanwhile, there have been efforts to use polybenzimidazole (PBI) in fuel cells.

However, many conventional fuel cells using PBI mimic the technology of phosphoric acid fuel cells, and MEA manufacturing methods also use electrodes for phosphoric acid fuel cells. In addition, the conventional PBI fuel cell uses a Nafion catalyst binder, the battery performance is greatly reduced.

Therefore, the present invention has been made to solve the above problems,

An object of the present invention is to eliminate the application of a low-performance Nafion type perfluorosulfonic acid polymer that has been conventionally used as a catalyst binder used in the production of fuel cell MEA electrodes, and enables fuel cell operation at high temperature and low humidity. It is to provide a polybenzimidazole catalyst binder, a method for producing the same and a membrane electrode assembly using the same.

An object of the present invention as described above is a catalyst binder used in the preparation of an electrode of a MEA comprising a membrane produced using a polybenzimidazole-based compound, and the catalyst binder characterized in that it comprises a polybenzimidazole Is achieved.

In addition, the pole Revenge imidazole is 3,3 ^'- diaminodiphenyl benzimidazolyl dynes (3, ^3' of the monomers -Diaminobenzidine) and isophthalic acid (isophthalic acid) or terephthalic acid (terephthalic acid), a poly phosphoric acid (polyphosphoric acid) or P ₂ O ₅ , and a polymer prepared by mixing and heating a mixture of any one or two of CF ₃ SO ₃ H or CH ₃ SO ₃ H and reacting.

The polybenzimidazole is more preferably a mixture of the mixture of CF ₃ SO ₃ H and CH ₃ SO ₃ H. In addition, the mixture is most preferably a volume ratio of 1: 1 of the CF ₃ SO ₃ H and CH ₃ SO ₃ H.

The catalyst binder is preferably a solution in which the polybenzimidazole is dissolved in a mixture of H ₃ PO ₄ and CF ₃ CO ₂ H. The catalyst binder is preferably a solution in which the polybenzimidazole is dissolved in DMAc or NMP.

An object of the present invention as described above, the method of manufacturing a catalyst binder is used in electrode manufacture of the MEA, 3,3 ^'- diamino-benzimidazolyl dynes ^(3,3' -Diaminobenzidine) and isophthalic acid (isophthalic acid), or The monomer of terephthalic acid is mixed with either polyphosphoric acid or P ₂ O ₅ and any one or two of CF ₃ SO ₃ H or CH ₃ SO ₃ H and heated to react. To prepare a polybenzimidazole (S1); And dissolving the polybenzimidazole in a solvent (S2).

In the step S1, it is preferable to use a mixture of both CF ₃ SO ₃ H and CH ₃ SO ₃ H as the mixture. In the step S1, the volume ratio of CF ₃ SO ₃ H and CH ₃ SO ₃ H is more preferably 1: 1.

In the step S2, the polybenzimidazole is preferably dissolved in a mixture of H ₃ PO ₄ and CF ₃ CO ₂ H. In the step S2, the polybenzimidazole is preferably dissolved in DMAc or NMP.

The object of the present invention as described above is achieved by a MEA comprising a membrane made of a polybenzimidazole-based compound, wherein the catalyst binder used in the production of the electrode comprises polybenzimidazole.

Hereinafter, a polybenzimidazole catalyst binder according to the present invention, a membrane electrode assembly using the same, and a method of manufacturing the same will be described in detail.

In the present invention, when forming a membrane of a fuel cell MEA using PBI or ABPBI, which is a polybenzimidazole-based compound (PBIs; polybenzimidazoles), the polymer used as a catalyst binder to maintain the adhesion between the membrane and the electrode, It should have a structure similar to the polymer used in the membrane.

Therefore, in the present invention, instead of the conventional Nafion type, a solution of polybenzimidazole is used as a catalyst binder used in the preparation of an electrode of an MEA having a membrane using a polybenzimidazole-based compound such as PBI or ABPBI.

Here, in particular, in the present invention is used as the pole Revenge imidazole-3,3 ^'- diamino-benzimidazolyl dynes ^(3,3' -Diaminobenzidine) and the monomers of isophthalic acid (isophthalic acid) or terephthalic acid (terephthalic acid), poly Mixed with a mixture of polyphosphoric acid or P ₂ O ₅ and CF ₃ SO ₃ H (or CH ₃ SO ₃ H, or CF ₃ SO ₃ H and CH ₃ SO ₃ H) Polybenzimidazole is prepared by reacting in a case where a mixture of both CF ₃ SO ₃ H and CH ₃ SO ₃ H is used as the mixture is not completely dissolved in an organic or inorganic solvent. And there is no problem that the obtained polybenzimidazole has a low molecular weight.

Furthermore, when the volume ratio of CF ₃ SO ₃ H and CH ₃ SO ₃ H in the mixture is 1: 1, excellent PBI which is well soluble in an organic solvent and has a high molecular weight suitable for a catalyst binder is obtained.

The solution of polybenzimidazole is obtained by dissolving the polymer of the polybenzimidazole obtained in a mixture of H ₃ PO ₄ and CF ₃ CO ₂ H, or in DMAc or NMP.

Subsequently, a catalyst slurry is prepared by mixing Pt / C as a catalyst in the solution, and coating the gas diffusion medium or a membrane (PBIs system) to complete the MEA.

Hereinafter, the present invention will be described in more detail by explaining preferred embodiments of the present invention. However, the present invention is not limited to the following examples, and various forms of embodiments can be implemented within the scope of the appended claims, and the following examples are merely common to those skilled in the art to complete the present disclosure. It is intended to facilitate the implementation of the invention to those with knowledge.

material

3,4-Diaminobenzoic acid was purchased from Acros and purified. Other reagents were used without further purification. From Aldrich Chemicals 3,3 ^'- diamino-benzimidazolyl dynes ^(3,3' -Diaminobenzidine), isophthalic acid _{(isophthalic acid), P 2 O} 5, methane sulfonic acid (methanesulfonic acid), trifluoromethanesulfonic acid ( trifluoromethanesulfonic acid, trifluoroacetic aicd and methanol were purchased.

Platinum catalyst (20 wt .-% Pt / C, Vulcan XC-72R, Alfa), carbon paper (Toray) and Nafion solution (5 wt .-% solution, Aldrich) were used for the MEA preparation.

Preparation of Acid Doped ABPBI Membrane

3,4-Diaminobenzoic acid (2 g), P ₂ O ₅ (3 g) and CH ₃ SO ₃ H (20 mL) were mixed together in a reactor maintained in a nitrogen (N ₂ ) atmosphere. The mixture was reacted at 150 ° C. for 30 minutes to obtain a high viscosity solution. This solution was applied onto a glass plate using a doctor blade to form an ABPBI membrane, and then the glass plate was immersed in water to remove the membrane. The prepared membrane was washed several times with water and dried in a vacuum oven.

ABPBI membranes doped with acid were obtained by immersing the ABPBI membrane in aqueous phosphoric acid (60 wt-% solution). 3.7 moles of H ₃ PO ₄ could be doped per 1 ABPBI repeat unit. Acid-doped ABPBI membranes have a proton conductivity of 0.06 S · cm ⁻¹ at 110 ° C. without external humidification, which is used as the membrane in the MEA of fuel cells for high temperature operation.

Synthesis of PBI and Preparation of Catalyst Slurry

1 is a view showing a chemical reaction formula for preparing a PBI in an embodiment of the present invention.

It demonstrates with reference to FIG. 3,3 ^'- diamino-benzimidazolyl dynes (2.42g, 11.3mol) and isophthalic acid (1.88g, 11.3mol) the _{P 2 O 5 (4g),} CF 3 SO 3 H (15mL) and CH ₃ SO ₃ H (15 mL) in a mixture. The reaction mixture was heated under nitrogen (N ₂ ) at 150 ° C. for 0.5 h. A homogeneous solution was obtained immediately and an increase in viscosity was observed. The hot polymer was poured into water (700 mL) to obtain fine powder using a peristaltic pump.

The powder was collected and washed several times with water. Until the phosphoric acid residue was no longer detected by the component analysis, the residual phosphoric acid in the polymer powder was extracted using a 10% ammonium hydroxide solution in a Soxhlet extractor to obtain an undoped polymer.

The polymer was dried and 3.5g was obtained for 2 days at reduced pressure, 50 ° C. (initial viscosity: 0.53 dL · g ⁻¹ , FTR-IR (KBr): 1630, 1527, 1455 cm ⁻¹ ).

Platinum catalyst slurries for electrodes in MEA were prepared by dissolving PBI (1 g) in a mixture of 85% H ₃ PO ₄ (3 g) and CF ₃ SO ₃ H (30 ml) and then mixing the platinum catalyst.

Viscosity Measurement / MEA Manufacturing / Operation

The viscosity measurement was performed through the following process. The polymer sample was dried at 80-90 ° C. under vacuum (0.1 mm Hg) for 30 hours. The polymer (0.5 g) was placed in a 100 ml volumetric flask and dissolved in 96% sulfuric acid (concentration 0.5 g dL ^-1 ). Solution viscosity was measured in a water bath at 30 ° C. using an Ubbelohde viscometer.

The cell efficiency of the MEA was measured through ULTIMA (Electrochem. Inc.). A catalyst slurry in which a platinum catalyst was mixed into a binder solution (a Nafion solution of Comparative Example described later or a solution of the above-described PBI) was coated through a doctor blade suitable for waterproofing carbon paper. The platinum catalyst and the polymer (Nafion solution of the comparative example or PBI solution of the example) in the electrode were 0.45 and 0.75 mg · cm ⁻² , respectively.

MEAs were formed by hot-pressing the electrodes on acid-doped ABPBI membranes at 1500 psi and 140 ° C. for 2 minutes. By injecting fuel and oxidant differently, a single cell was operated at 120, 140 and 160 ° C without external humidification.

result

^{PBI (poly [ '- (m} -phenylene-5,5' 2,2 -bibenzimidazole] as described above) is in the polymerization medium by using the _{CF 3 SO 3 H, CH 3} SO 3 H and P ₂ O ₅ The ratio of CF ₃ SO ₃ H and CH ₃ SO ₃ H was varied with respect to the fixed amount of monomer and the amount of P ₂ O ₅ during the polymerization Table 1 shows the viscosity of the polymers.

CF ₃ SO ₃ H (mL) CH ₃ SO ₃ H (mL) Intrinsic Viscosity (dLg- ¹ ) ^a 30 0 ^-b 21 9 0.81 18 12 0.69 15 15 0.53 0 30 0.34

a: Intrinsic viscosity was measured at 30 degreeC. The PBI concentration of the sulfuric acid solution was 0.5 g · dL ⁻¹ .

b: PBI was partially dissolved in sulfuric acid.

When only CF ₃ SO ₃ H was used for the polymerization, the resulting PBI was not completely dissolved in organic or inorganic solvents. When CH ₃ SO ₃ H was used as the sole solvent in the polymerization, a low molecular weight PBI was obtained.

In the present invention, particularly, when the volume ratio of CF ₃ SO ₃ H and CH ₃ SO ₃ H is 1: 1, PBI having sufficient high molecular weight suitable for binding the catalyst can be obtained.

FIG. 2 is a graph showing the effect of operating temperature on the efficiency of a single fuel cell, with ABPBI doped with 370 mol% H ₃ PO ₄ , no external humidification, and the catalyst loading was 0.45 mg · cm ⁻² platinum The PBI loading was 0.75 mg · cm ⁻² , the fuel was hydrogen, the oxidant was oxygen, and the cell size was 18 cm ² . The operating temperature is 120 ° C, ■ 140 ° C, and ▲ ° 160 ° C.

As shown in FIG. 2, the efficiency increases as time increases, as is the case for PBI type polymers. The single fuel cell test provided a current density of about 280 mAcm ⁻² without external humidification when injecting hydrogen and oxygen at 160 ° C.

Cell efficiency was also measured for other fuel injections. 3 shows that the fuel cell shows no efficiency loss when a mixture of hydrogen and carbon monoxide (100 ppm) is used as the injection fuel at 160 ° C. In FIG. 3 the operating temperature was 160 ° C. ABPBI was doped with 370 mol% H ₃ PO ₄ , no external humidification, catalyst loading was 0.45 mg · cm ⁻² platinum, 0.75 mg · cm ⁻² PBI loading, oxidant was air, cell size Was 18 cm ² . Fuel injection ● the H ₂ + CO 100ppm, ▲ represents the H ₂ alone.

As mentioned above, a single fuel cell with a catalyst layer fabricated using Nafion as the binding polymer was fabricated for comparison with the case with PBI.

The catalyst slurry was prepared from a mixture of Nafion solution (20 g, 5 wt .-% solution), water (10 mL) and 85% H ₃ PO ₄ (3 g).

4 shows a polarity curve of an ABPBI-based MEA using a Nafion binder. ABPBI was doped with 370 mol% H ₃ PO ₄ , no external humidification, catalyst loading was 0.45 mg · cm ⁻² platinum, Nafion loading 0.75 mg · cm ⁻² , oxidant was oxygen, cell The size was 18 cm ² . The operating temperature was 120 ° C for ●, 140 ° C for ■, and 160 ° C for ▲.

As shown in FIG. 4, the cell efficiency at all temperatures is about the same. Nafion does not have high proton conductivity at low moisture and high temperature conditions, but PBI binders perform more proton conduction at each temperature than Nafion binders.

According to the present invention, unlike the low performance Nafion type perfluorosulfonic acid polymer that has been conventionally used, it is possible to operate a fuel cell in a high temperature and low humidity state.

In addition, according to the present invention, polybenzimidazole for a catalyst binder which is soluble in organic and inorganic solvents and has a sufficient high molecular weight suitable for a catalyst binder can be obtained.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

Claims (8)

It is a catalyst binder used in the preparation of the electrode of the membrane electrode assembly comprising a membrane prepared using a polybenzimidazole-based compound, The catalyst binder pole Revenge, and imidazole, the pole Revenge imidazole is 3,3 ^'- diaminodiphenyl benzimidazolyl dynes ^(3,3' -Diaminobenzidine) and isophthalic acid (isophthalic acid) or terephthalic acid (terephthalic acid) Is a polymer prepared by mixing and heating a monomer of polyphosphoric acid (polyphosphoric acid) or P ₂ O ₅ and CF ₃ SO ₃ H and CH ₃ SO ₃ H in a mixture mixed and heated Catalyst binder. delete delete The method of claim 1, The mixture is a catalyst binder, characterized in that the volume ratio of the CF ₃ SO ₃ H and CH ₃ SO ₃ H 1: 1. In the method of producing a catalyst binder used in the production of the electrode of the membrane electrode assembly, 3,3 ^'- diamino-benzimidazolyl dynes ^(3,3' -Diaminobenzidine) and of isophthalic acid (isophthalic acid) or terephthalic acid monomers, poly phosphoric acid (polyphosphoric acid) or P ₂ O ₅ of (terephthalic acid) Any one, and mixing the mixture of CF ₃ SO ₃ H and CH ₃ SO ₃ H and heated to react to prepare a polybenzimidazole (S1); And Dissolving the polybenzimidazole in a solvent (S2); The method of producing a catalyst binder comprising a. delete The method of claim 5, The step S1 is a method of producing a catalyst binder, characterized in that the volume ratio of the CF ₃ SO ₃ H and CH ₃ SO ₃ H 1: 1. In the membrane electrode assembly, A membrane electrode assembly comprising a membrane prepared using a polybenzimidazole compound, and wherein the catalyst binder used in electrode production is the catalyst binder according to claim 1 or 4.

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