KR20170108676A - Asymmetric microporous polybenzimidazol membrane - Google Patents

Abstract

The present invention relates to an asymmetric porous polybenzimidazole membrane. By developing the asymmetric porous polybenzimidazole membrane which can be used in high temperature hydrogen exchange membrane fuel cells, it is possible to prevent reduction in performance due to fuel cross-over, phosphoric acid leak, and stability caused by acid doping rate and high ion conductivity shown on existing porous polybenzimidazole membranes.

Description

ASYMMETRIC MICROPOROUS POLYBENZIMIDAZOL MEMBRANE [0001] This invention relates to asymmetric porous polybenzimidazole membranes,

The present invention relates to a polybenzimidazole membrane, and more particularly, to a polybenzimidazole membrane which is applied to an energy generating element such as a fuel cell and which has excellent stability and durability at high temperature and maximizes ionic conductivity to provide an asymmetric porous poly Benzimidazole < / RTI >

As problems arise due to global warming and energy depletion, fuel cells are attracting attention as environmentally friendly and highly efficient next generation energy sources. Fuel cells are promising energy conversion systems that can replace traditional low-efficiency power generation technologies. This is a non-combustion energy generating device unlike an internal combustion engine, and is not only considered as an environmentally friendly power generating device because it does not generate harmful exhaust gas during combustion, and is also excellent in efficiency compared to an internal combustion engine.

Among various types of fuel cells, research on a proton exchange membrane fuel cell (PEMFC) has been actively conducted. Most cation exchange membranes of PEMFCs are made from perfluorosulfonic acid, Nafion. Nafion membranes exhibit cationic conductivity, which is highly dependent on their moisture content, thus requiring membrane drying through proper moisture control. For this reason, Nafion based membranes are generally used limited to operating temperature ranges up to 80 ° C at atmospheric pressure.

Accordingly, efforts are being made to develop fuel cells that can operate at low temperatures. However, due to the necessity of secondary elements such as a hydrogen storage tank, a hydrocarbon or alcohol reforming device and accompanying carbon monoxide removing device, the fuel cell device becomes complicated, which increases the cost.

In recent years, methods for operating a fuel cell at temperatures higher than 80 ° C have been proposed. In a typical fuel cell membrane, water is used as an important factor in determining the physical properties, considering the thermal, chemical and mechanical stability of the polymer used and the fact that the cation is conducted mainly by a vehicle or a hopping mechanism. Therefore, when the fuel cell is operated at a temperature of 100 ° C or higher, the water evaporates from 80 ° C, and when the operating temperature is 200 ° C, the pressure of the saturated water vapor becomes 15 atm. . In addition, the cooling design and the efficiency of the fuel cell are determined by the temperature difference between the battery and the surroundings. If the temperature is increased from 80 ° C to 200 ° C, the size of the radiator will increase by 3 or 4 times. . Especially, when the operating temperature is increased, there is a problem that the usability of the electrode against carbon monoxide and sulfide, which are fuel impurities, increases.

Complexation of acid and base increases the efficiency of the cation exchange membrane. Polymers with ether, alcohol, imine, amide or imide groups act as cationic receptors and form strong acid and ion pairs. Until now, the polymer used for cation exchange has been doped with acid and showed high cation conductivity. Considering such a cation conduction mechanism, phosphoric acid or phosphorous acid acts as a cation donor or acceptor to form a dynamic hydrogen bond, is low in vapor pressure and is thermally stable and suitable for use as an acid. Most polymer-acid combinations exhibit cation conductivity of 10 ^-3 S cm ^-1 at room temperature. As the content of acid increases, it becomes difficult to produce a membrane because it is a paste-like phase. An acid-doped polybenzimidazole (PBI) film can be used to solve this problem. Phosphoric acid-doped polybenzimidazole and fuel cells have operating temperatures from ambient to 200 ° C, have high cation conductivity, good mechanical strength and thermal stability. Further, it is known that the influence by moisture is small, the tolerance to carbon monoxide is large, and it has a good thermal efficiency.

Korean Patent Publication No. 2001-0030409 (Apr. 16, 2001)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a polybenzimidazole membrane and a method of manufacturing the same, which can increase the amount of acid doping and improve ionic conductivity, The purpose is to do.

It is another object of the present invention to provide a polybenzimidazole membrane capable of preventing physical stability and acid leakage after doping, and a process for producing the polybenzimidazole membrane.

In order to achieve the above object, the present invention provides an asymmetric porous polybenzimidazole membrane comprising a dense layer on one side and a porous layer on the other side corresponding to the polybenzimidazole membrane.

In the asymmetric porous polybenzimidazole membrane according to an embodiment of the present invention, the porous layer may be a region in which pores having an average pore size of 0.01 to 10 μm are distributed.

In the asymmetric porous polybenzimidazole membrane according to an embodiment of the present invention, the porous layer may be 10 to 90% of the total membrane thickness.

The asymmetric porous polybenzimidazole membrane according to an embodiment of the present invention may have a thickness of 15 to 30 mu m.

The asymmetric porous polybenzimidazole membrane according to one embodiment of the present invention may have a tensile strength of 70 to 110 MPa and an elongation percentage of 5 to 65%. The asymmetric porous polybenzimidazole membrane according to the present invention may have an oxygen permeability of 130 to 170 cm ³ / (m ² · 24 hr · atm).

In addition,

Preparing a first solution comprising polybenzimidazole and a solvent,

Preparing a second solution for mixing the porogen with the first solution,

Applying the second solution on a substrate to form a film, and

And heat-treating the applied film. The present invention also provides a method for producing an asymmetric porous polybenzimidazole membrane.

In the method of manufacturing an asymmetric porous polybenzimidazole membrane according to an embodiment of the present invention, the second solution may further be allowed to stand at a temperature ranging from -20 to 5 ° C.

In an asymmetric porous polybenzimidazole membrane production method according to an embodiment of the present invention, the content of the second solution phase porogen may be 30 to 55 wt%.

In the method of manufacturing an asymmetric porous polybenzimidazole membrane according to an embodiment of the present invention, the step of forming the film may be a step of applying a second solution on a substrate to a thickness of 100 to 250 탆.

In the asymmetric porous polybenzimidazole film according to an embodiment of the present invention, the heat treatment may be performed at a temperature ranging from 25 to 400 ° C.

The asymmetric porous polybenzimidazole membrane according to the present invention can be used in a high temperature hydrogen-exchange membrane fuel cell and can realize high ionic conductivity.

In addition, the asymmetric porous polybenzimidazole membrane of the present invention has an advantage of preventing physical degradation due to acid doping and performance deterioration due to acid leakage.

1 is a photograph showing the upside and the downside of a polybenzimidazole (PBI) film according to Comparative Examples 1, 2 and Examples 1, 2,
2 is an SEM photograph showing the surface and cross-section of the PBI film according to Comparative Example 1. Fig.
3 is an SEM photograph showing a surface and a cross section of a PBI film according to Comparative Example 2. Fig.
4 is a SEM photograph showing the surface and cross-section of the PBI film according to Example 1. Fig.
5 is a SEM photograph showing the surface and cross-section of the PBI film according to Example 2. Fig.
6 is an SEM photograph showing the surface and cross-section of the PBI film according to Example 3. Fig.
7 is a pore size distribution diagram of a PBI membrane according to Comparative Example 2 and Examples 1, 2, and 3.
FIG. 8 is a TGA graph for evaluating the thermal stability of PBI films according to Comparative Examples 1, 2 and Examples 1, 2, and 3.
FIG. 9 is a graph showing the phosphoric acid doping ratio and doping level of PBI films according to Comparative Examples 1, 2, and Examples 1, 2, and 3.
10 is a graph showing the ionic conductivity of PBI films according to Comparative Examples 1 and 2 doped with phosphoric acid and Examples 1, 2 and 3. FIG.

Hereinafter, the asymmetric porous polybenzimidazole membrane of the present invention and its production method will be described in detail. The present invention may be better understood by the following examples, which are for the purpose of illustration only and are not intended to limit the scope of protection defined by the appended claims. The technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs, unless otherwise defined.

Recently, development of a reliable fuel cell capable of operating at a high temperature in terms of performance efficiency has been required. Here, the high temperature refers to a temperature exceeding 80 캜. In particular, fuel cells operating at high temperatures, such as automobiles, are required to have high efficiency and durability over a high temperature range. In this sense, polybenzimidazole resin, which is a basic amorphous polymer having excellent thermal and mechanical properties, is attracting attention as a high performance polymer electrolyte membrane as a fuel cell material. Moreover, in view of the fact that the catalysts of fuel cells operating at high temperatures are included in the exhaust gas, this is more so in that the tolerance of the electrodes to carbon monoxide or sulphide is increased. Accordingly, although not limited to any particular theory, it is presumed that the asymmetric porous polybenzimidazole membrane according to the present invention has a higher ionic conductivity than the conventional polybenzimidazole membrane, and the disadvantage of the porous polybenzimidazole membrane There is an excellent advantage in that it can prevent fuel crossover and acid leakage.

In addition, the present invention is applicable to various fields such as energy storage devices such as secondary batteries and redox flow cells, gas separation membranes, and the like, without being limited to those applied in high temperature polymer membrane fuel cells and solid alkaline fuel cells of renewable energy, High efficiency and long-term durability can be realized.

The present invention is characterized in that, in providing a porous polybenzimidazole membrane, the membrane structure is an asymmetric membrane. Specifically, the asymmetric membrane includes a dense layer on one side and a porous layer on the other side corresponding to the dense layer. In one embodiment, the asymmetric membrane has a structure in which pore structures on both surfaces are asymmetric with respect to each other, and includes a meaning having an asymmetric structure in a porous homogeneous membrane, more preferably, And a porous layer in which a relatively large pore layer is formed.

The term " asymmetric " in the present invention means a change in the average pore structure which is formed in a direction transverse to the membrane itself or a cross section (i.e., vertical section) of a specific region in the membrane. In addition, the asymmetric membrane may comprise an average pore structure that varies across the membrane (typically, the average pore size). Further, the dense layer and the porous layer mean that there is no interrupted portion between the dense layer and the porous layer, and the dense layer and the porous layer can not be visually confirmed but the pores are connected to each other to form a flow path.

In the present invention, the porous layer can be distinguished from the dense layer based on a boundary line in a direction crossing the cross section of the membrane, based on a SEM photograph of a magnification of 10K.

In this regard, the asymmetric porous polybenzimidazole membrane according to the present invention may have a thickness ratio of the porous layer of 10 to 90% based on the total thickness. And preferably 60 to 85%. When the above range is satisfied, there is an excellent characteristic in that fuel crossover and acid leakage which is a disadvantage of the porous polybenzimidazole film can be prevented and physical stability can be ensured after doping the acid.

The porous layer is a region in which pores having a pore size of 0.01 탆 or more are distributed, and corresponds to a dense layer. More specifically, in the present invention, the porous layer is a region in which pores with an average pore size of 0.01 to 10 탆 are distributed, preferably 0.1 to 5 탆, more preferably 0.2 to 2.0 탆 have.

In addition, the asymmetric porous polybenzimidazole membrane according to the present invention may have a thickness of 15 to 30 mu m, preferably 20 to 25 mu m. Accordingly, the thickness of the porous layer in the asymmetric porous polybenzimidazole membrane is preferably 2 to 27 탆, more preferably 3 to 22 탆. The thinner the film, the lower the resistance of the film, which improves the performance when applied to an actual fuel cell. More preferably, the thickness of the film is 20-25 탆.

In the present invention, polybenzimidazole (PBI) includes aromatic heterocyclic polymers containing benzimidazole monomers. In addition, PBI having a different structure can be synthesized from different combinations of tetraamine and dibasic acids or from a diamine acid in combination. As a specific example, polybenzimidazole is a commercially available product, which is a poly 2,2'-m- (phenylene) -5,5 ', N'-dicyclohexylmethane, called mPBI contained in Danish Power system (DPS) -Bibenzimidazole. ≪ / RTI >

The polybenzimidazole may also be a PBI mixture, a crosslinked PBI, a PBI compound or a modified type of PBI such as para-PBI (poly [2,2'-p- (phenylene) -5,5'- (2,2 '- (2,6-naphthalene) -5,5', 4,4'-tetramethyluronium hexafluorophosphate), pyridine-based PBI, AB- -Bibenzimidazole]), Py-PBI (poly [2,2 '- (2,6-pyridine) -5,5'-bibenzimidazole]), Py-O-PBI, dihydroxy- Substituted PBI such as poly (N-methylbenzimidazole) or poly (N-ethylbenzimidazole), sulfonated PBI, or an acid or base such as hexafluorophosphate PBI But is not limited to, any other polymer capable of cation conduction at temperatures above 120 ° C with or without doping.

The asymmetric porous polybenzimidazole membrane according to the present invention may have a tensile strength of 70 to 110 MPa and an elongation percentage of 5 to 65% as measured using a universal testing machine (UTM).

The asymmetric porous polybenzimidazole membrane according to the present invention may have an oxygen permeability of 130 to 170 cm ³ / (m ² · 24 hr · atm). At this time, the oxygen permeability was measured through a filter tester (Capillary flow porometer, manufactured by PMI) under oxygen pressure of 60 psi.

The present invention provides a method for forming a film comprising the steps of preparing a first solution containing polybenzimidazole and a solvent, preparing a second solution for mixing the porogen with the first solution, applying the second solution onto the substrate to form a film And heat-treating the applied film. The present invention also provides a method for producing an asymmetric porous polybenzimidazole membrane.

Specifically, in the method for preparing an asymmetric porous polybenzimidazole membrane according to the present invention, the step of preparing the first solution is a step of mixing polybenzimidazole and at least one solvent, wherein the solvent is polyimide- The solvent is not particularly limited as long as it dissolves completely, and preferably a polar solvent can be used. Examples of the solvent include dimethylacetamide (DMAc), dimethylformamide (DMF), NN-methylpyrrolidone (NMP), N-methylpyrrolidone, tetramethylurea, dioxane, diethylsuccinate, dimethylsulfoxide, Chloroform, tetrachloroethane, and mixtures thereof. It is more preferable to use dimethylacetamide (DMAc).

Next, a step of preparing a second solution for mixing the porogen with the first solution prepared is carried out. As the porogen, any one or more selected from among alcohol compounds, polyethylene glycol compounds, esters or ether compounds and various salt compounds can be used, but it is preferable to use dibutyl phthalate as a target effect of the present invention It is more efficient to implement.

At this time, it is more preferable that the porogen content is 30 to 55% by weight, preferably 40 to 50% by weight. When the above range is satisfied, it is more advantageous to form the pores and to realize the asymmetric porosity of the membrane and the mechanical properties and the high ion conductivity.

Further, the second solution may further comprise a step of setting at a temperature in the range of -20 to 5 [deg.] C. If the step of setting in the temperature range is further carried out, the degree of asymmetry of the film can be maximized, and the effect thereof can be further improved.

The step of preparing the second solution may then be performed by applying the second solution onto the substrate to form a film. The method of forming the film is not critical, but may be cast by various devices. For example, a spreader such as an extrusion die or a slot coater, a doctor blade, a spray pressurizing device, and the like can be mentioned.

In the step of forming the membrane, the polybenzimidazole and the porogen are phase-separated due to the difference in specific gravity, and the porogen is located at the lower end in the thickness direction due to gravity, and due to the evaporation of the porogen during drying, To form an asymmetric porous polybenzimidazole membrane having an asymmetric structure comprising a layer and a porous layer on the other side corresponding thereto. At this time, the thickness for applying the second solution on the substrate is preferably 100 to 250 mu m. When the above range is satisfied, the film is formed well.

Adjusting the coating thickness in the coating step is carried out considering that the thickness of the doped film is increased with respect to the coating thickness before doping the acid, that is, doping the acid in the subsequent step. The thickness of the doped layer is preferably 25 to 55 μm, more preferably 30 to 50 μm. When the thickness is in the above range, the membrane resistance can be lowered when applied to a fuel cell, and the fuel cell performance is better. On the other hand, when the thickness of the film after doping is less than the above range, fuel crossover may occur or mechanical properties may deteriorate.

The film thus coated is heat treated. The heat treatment process may be carried out during the casting process. The heat treatment temperature range is 25 to 400 캜, preferably 80 to 120 캜. When the heat treatment temperature range satisfies the above range, the removal of the organic solvent is smooth and is better in terms of the formation of the film having the desired physical properties.

The film obtained after the heat treatment can be cleaned. At this time, the washing may be carried out using an alcohol such as methanol or distilled water, preferably by immersing in a mixed solution of methanol and distilled water for 6 to 24 hours. Through this cleaning process, the porogen can be removed.

The asymmetric porous polybenzimidazole membrane according to the present invention described above is used as a fuel cell together with a cathode and an anode containing catalyst means. At this time, the operating temperature of the fuel cell may be in the range exceeding 80 ° C, preferably 80 ° C to 250 ° C, more preferably 120 to 230 ° C. The asymmetric porous polybenzimidazole membrane is used acid-doped, where the acid may be phosphoric acid or other acid which is thermally stable at the fuel cell operating temperature with a low vapor pressure equivalent to phosphoric acid. Preferably, the asymmetric porous polybenzimidazole membrane can be doped with a phosphoric acid solution of 50% or more, more preferably 60% or more.

Hereinafter, an asymmetric porous polybenzimidazole membrane according to the present invention will be described. However, the present invention is not limited to the following examples.

(Comparative Example 1)

Manufacture of mPBI

2 g of polybenzimidazole (Dapozolⓡ, Danish Power system (DPS), Denmark) and 18 g of DMAC are placed in a round three-necked flask and dissolved in a refluxed atmosphere at 120 캜 for 12 hours through a reflux atmosphere (10 wt% solution). Thereafter, the temperature of the solution was lowered to room temperature of 20 占 폚, and then the glass substrate was cast with a doctor blade to a thickness of 250 占 퐉 on a glass plate. Thereafter, the glass plate on which the film was formed was dried in a dry oven at 25 ° C to 80 ° C at a heating rate of 1 ° C / min for 8 hours, and then heated to 120 ° C again at a heating rate of 0.5 ° C / min. Next, the sample was treated in a vacuum condition for 12 hours, immersed in distilled water to remove the film from the glass plate, and dried in a dry oven at 80 ° C.

(Comparative Example 2)

Preparation of P-PBI 70

2 g of polybenzimidazole (Dapozolⓡ, Danish Power system (DPS)) and 18 g of dimethylacetamide (DMAc) were placed in a round three-necked flask and reflux was performed at 120 ° C. for 12 hours in a nitrogen- (10 wt% solution prepared). Then, 4.7 g of dibutyl phthalate (Sigma aldrich, DBP) was added and mixed for 3 hours. Next, the temperature of the solution was lowered to room temperature of 20 占 폚, and then the glass substrate was cast to a thickness of 250 占 퐉 on a glass plate using a doctor blade. Thereafter, the glass plate on which the film was formed was dried in a dry oven at 120 ° C for 8 hours, treated in a vacuum condition for 12 hours, and then immersed in distilled water to remove the film from the glass plate. 12 hours of methanol was added thereto in a mixture of methanol / distilled water (1: After soaking for a time, it was dried in a dry oven at 80 ° C.

(Example 1)

Preparation of P-PBI 47

2 g of polybenzimidazole (Dapozolⓡ, Danish Power system (DPS), Denmark) and 18 g of DMAC are placed in a round three-necked flask and dissolved in a refluxed atmosphere at 120 캜 for 12 hours through a reflux atmosphere (10 wt% solution). Thereafter, 1.8 g of dibutyl phthalate (Sigma aldrich, DBP) was added and mixed for 3 hours. Next, the temperature of the solution was lowered to room temperature of 20 ° C, and the solution was allowed to stand in a refrigerator (2 to 3 ^° C) for 12 hours or more. Thereafter, the mixture was stirred at room temperature for 10 minutes using a stirrer, and then cast onto a glass plate with a doctor blade to a thickness of 250 탆 on a glass plate. Next, the glass plate on which the film was formed was dried in a dry oven at 25 ° C to 80 ° C at a rate of 1 ° C / min for 8 hours, and then heated to 120 ° C at a rate of 0.5 ° C / min. Next, the film was treated in a vacuum condition for 12 hours, immersed in distilled water to remove the film from the glass plate, immersed in methanol for 12 hours, mixed with methanol / distilled water (1: 1) for 12 hours, and dried in a dry oven at 80 ° C.

(Example 2)

Preparation of P-PBI 44

2 g of polybenzimidazole (Dapozolⓡ, Danish Power system (DPS), Denmark) and 18 g of DMAC are placed in a round three-necked flask and dissolved in a refluxed atmosphere at 120 캜 for 12 hours through a reflux atmosphere (10 wt% solution). Thereafter, 1.6 g of dibutyl phthalate (Sigma aldrich, DBP) was added and mixed for 3 hours. Next, the temperature of the solution was lowered to room temperature of 20 ° C, and the solution was allowed to stand in a refrigerator (2 to 3 ^° C) for 12 hours or more. Thereafter, the mixture was stirred at room temperature for 10 minutes using a stirrer, and then cast onto a glass plate with a doctor blade to a thickness of 250 탆 on a glass plate. Next, the glass plate on which the film was formed was dried in a dry oven at 25 ° C to 80 ° C at a rate of 1 ° C / min for 8 hours, and then heated to 120 ° C at a rate of 0.5 ° C / min. Next, the film was treated in a vacuum condition for 12 hours, immersed in distilled water to remove the film from the glass plate, immersed in methanol for 12 hours, mixed with methanol / distilled water (1: 1) for 12 hours, and dried in a dry oven at 80 ° C.

(Example 3)

Preparation of P-PBI 41

2 g of polybenzimidazole (Dapozolⓡ, Danish Power system (DPS), Denmark) and 18 g of DMAC are placed in a round three-necked flask and dissolved in a refluxed atmosphere at 120 캜 for 12 hours through a reflux atmosphere (10 wt% solution). Then, 1.4 g of dibutyl phthalate (Sigma aldrich, DBP) was added and mixed for 3 hours. Next, the temperature of the solution was lowered to room temperature of 20 ° C, and the solution was allowed to stand in a refrigerator (2 to 3 ^° C) for 12 hours or more. Thereafter, the mixture was stirred at room temperature for 10 minutes using a stirrer, and then cast onto a glass plate with a doctor blade to a thickness of 250 탆 on a glass plate. Next, the glass plate on which the film was formed was dried in a dry oven at 25 ° C to 80 ° C at a rate of 1 ° C / min for 8 hours, and then heated to 120 ° C at a rate of 0.5 ° C / min. Next, the film was treated in a vacuum condition for 12 hours, immersed in distilled water to remove the film from the glass plate, immersed in methanol for 12 hours, mixed with methanol / distilled water (1: 1) for 12 hours, and dried in a dry oven at 80 ° C.

(evaluation)

In order to analyze the surface and cross-section of the comparative examples 1, 2, and 1, 2, and 3, an SEM was confirmed. In the porous layer on one side and the porous layer on the other side, And the pore size distribution of the pores is shown in FIG. In addition, TGA analysis was carried out to evaluate the thermal stability of Comparative Examples 1, 2 and Examples 1, 2, and 3, and conditions were performed at room temperature to 750 ° C at a rate of 10 ° C / min in an air atmosphere.

To measure the phosphoric acid doping ratios of Comparative Examples 1, 2, and 1, 2, and 3, a film was dipped in a phosphoric acid solution of 85% for 4 days and then dried at 100 ° C for 12 hours. And the phosphorus content and the doping level are shown in FIG.

In order to test the physical stability of Comparative Examples 1, 2, and 1, 2, and 3, the membrane was dipped in a phosphoric acid-doped sample (85% phosphoric acid solution (Sigma Aldrich)) and dipped for 4 days) At the same time, a tensile strength test was conducted. At this time, the sample shape was dumbbell, and the actual measurement width was 2 mm and the length was 30 mm, and three or more samples were measured to obtain an average value. At this time, the test was performed using a universal material testing machine (Testometric Micro 350) under conditions of 10.00 mm min ^-1 .

Further, in order to measure ionic conductivities of Comparative Examples 1, 2 and Examples 1, 2 and 3, a film doped with phosphoric acid (85% phosphoric acid solution (sigma aldrich) And was measured with no humidity at a temperature range of 60 to 180 캜. The electrolyte membrane ionic conductivity was measured using an impedance spectroscopy (Bio-Logics 150, France) and an alternating current source with a voltage range of 1 mV to 10 mV in a frequency range of 1 to 105 Hz in a four-electrode system. The impedance R value of the polymer electrolyte membrane was calculated by the following equation.

(Equation 1)? =

Where R is the impedance of the polymer electrolyte membrane, W is the width of the membrane (cm), and d is the thickness (cm) of the membrane.

1 is a photograph showing the upside and the downside of PBI films according to Comparative Examples 1, 2 and Examples 1, 2, and 3. In the case of Examples 1, 2, and 3, And the lower surface of the lower surface was formed with pores, and thus the surface was brighter than the upper surface. Also, in the case of mPBI (Comparative Example 1), which is a dense film, there is no pore and the film is in the form of a transparent film, whereas the membranes having pores are permeated by pores. This confirmed that the asymmetric porous membrane was formed through FIGS. 4, 5 and 6, and it was confirmed that Comparative Example 2 was also a porous membrane.

FIG. 7 is a pore size distribution diagram of the PBI membrane according to Comparative Example 2 and Examples 1, 2, and 3, and it is possible to control the pore size formation including the combination of PBI and porogen and the content thereof. The PBI membrane (P-PBI 47) according to Example 1 showed that the pore size of the porous layer was 0.4 to 3.1 mu m and the average pore size was 1.72 mu m. The PBI membrane (P-PBI 44) according to Example 2 was found to be 0.2 to 2 占 퐉 and the average pore size to be 0.94 占 퐉. Further, the PBI membrane (P-PBI 41) according to Example 3 had a pore size of 0.055 to 0.44 mu m and an average pore size of 0.2 mu m. When the pore size is small, the amount of acid to be doped in the film may be limited. If the above range is satisfied, the amount of doping can be increased by forming a space in which pores can be doped with acid, and the ion conductivity according to the flow path can be improved. On the other hand, if the pore size is too large or the distribution is excessive as in Comparative Example 2, the doping rate may be increased, but mechanical properties of the membrane may be deteriorated due to excessive acid.

8 is a TGA graph for evaluating the thermal stability of the PBI films according to Comparative Examples 1, 2, and Examples 1, 2, and 3. The TGA graphs of Comparative Examples 1, 2, The results show similar trends. In the case of polybenzimidazole, weight loss of 5 ~ 10% was observed due to the removal of water up to 150 ° C. No significant weight loss was observed up to 500 ° C above the above temperature, and the weight change due to the release of carbon dioxide . However, since the weight reduction at 400 ° C or less does not occur, it has been confirmed that thermal stability can be secured as a material for a high temperature fuel cell.

FIG. 9 is a graph showing the doping ratios and doping levels of the PBI films according to Comparative Examples 1, 2, and Examples 1, 2, and 3. As the content of porogen increases, the porosity increases and the doping ratio of phosphoric acid increases Respectively. In the case of Comparative Example 2, which is a porous membrane, the content of phosphoric acid was 2 times higher than that of Comparative Example 1 which is a non-porous membrane and 1.6 times higher than that of Example 1 (P-PBI 47) which is an asymmetric porous membrane.

The polybenzimidazole according to the present invention has an excellent mechanical strength since the -N = and -NH- groups form a main intermolecular force and the chain is packed tightly. Table 1 below shows the tensile strengths of the PBI films according to Comparative Examples 1, 2 and Examples 1, 2 and 3, and shows the tensile strength of the PBI film before and after phosphoric acid doping.

[Table 1]

Comparative Examples 1 and 2 and Examples 1, 2 and 3 before the phosphoric acid doping show a tensile strength of about 71 to 118 MPa. In the case of an asymmetric porous membrane having porosity controlled by the content of porogen, Tensile strength has decreased somewhat. However, Examples 1, 2, and 3 of the present invention show higher tensile strength than Comparative Example 2 (P-PBI 70), which is a porous membrane. Also, in Comparative Examples 1 and 2 and Examples 1, 2 and 3 in which phosphoric acid was introduced, the hydrogen bonding between the polybenzene imidazole chains was attenuated when 2% of phosphoric acid was introduced, but hydrogen bonds were formed between the phosphoric acid and nitrogen atoms So that there is no change in the modulus or tensile strength of the polybenzeneimidazole. However, when the number of moles of phosphoric acid is larger than the number of moles of base, the free acid is increased and the distance between PBI chains is distant and the tensile strength is rapidly decreased. In Examples 1, 2 and 3 showing high doping ratios, the tensile strengths after phosphoric acid doping were lower than those of Comparative Example 1. It can be confirmed that it has higher tensile strength and modulus than Comparative Example 2 which is a porous membrane.

FIG. 10 is a graph showing the ionic conductivity of PBI films according to Comparative Examples 1 and 2 and Examples 1, 2 and 3 doped with phosphoric acid. When the acid content of acid-doped PBI is low, acid is used to bisect the nitrogen sites, As shown in Fig. The exchange of protons is carried out between the cationized nitrogen and the non-cationized neighboring chain, so that the ionic conductivity is less than 10 ^-7 S / cm. When the doping reaches the 4-6 level, the migration of proton depends on the content of the acid and the anion chain (H ₂ PO ₄ ^- H ⁺ ... H ₂ PO ₄ ⁺ ) or acid and water (H ₂ PO ₄ ^- H ⁺ ... H ₂ PO ₄ ⁺ ) chain. In this case, the conduction mechanism is similar to a concentrated phosphoric acid solution. In the case of Examples 1, 2 and 3, the conductivity was improved by the higher phosphoric acid doping ratio than that of Comparative Example 1. In Comparative Example 2, the highest phosphoric acid doping level was observed. However, Showed a drastic decrease in performance after 120 ° C. Comparative Example 1 and Examples 1, 2, and 3 showed a decrease in performance after 160 ° C, but the performance of the fuel cell due to the hydrolysis of phosphoric acid resulted in deterioration in performance due to water generated in the anode and moisture of the fuel supplied I do not think so. Thus, it was confirmed that Examples 1 and 2 according to the present invention exhibited higher stability than the conventional porous polybenzimidazole membranes, and showed higher performance than Comparative Example 1. FIG.

Table 1 below shows the results of oxygen permeability (unit: cm ³ / ((m ² · 24 hr · atm)) measured according to ASTM D3985 of Comparative Examples 1 and 2 and Examples 1 and ² , The asymmetric porous PBI membrane according to Examples 1 and 2 exhibited oxygen permeability similar to that of the mPBI single membrane of Comparative Example 1. The oxygen permeability was significantly lower than that of Comparative Example 2 which was a porous membrane. And at the same time, it can solve the problem of the existing porous membrane, fuel crossover.

[Table 2]

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Various modifications and variations are possible in light of the above teachings.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (10)

As polybenzimidazole membranes,
An asymmetric porous polybenzimidazole membrane comprising a dense layer on one side and a porous layer on the other side corresponding thereto.
The method according to claim 1,
Wherein the porous layer has an average pore size of from 0.01 탆 to 10 탆.
The method according to claim 1,
Wherein the porous layer is 10 to 90% of the total thickness of the membrane.
The method according to claim 1,
The asymmetric porous polybenzimidazole membrane has a thickness of 15 to 30 占 퐉.
The method according to claim 1,
Wherein the membrane has a tensile strength of 70 to 110 MPa and an elongation percentage of 5 to 65%.
Preparing a first solution comprising polybenzimidazole and a solvent,
Preparing a second solution for mixing the porogen with the first solution,
Applying the second solution on a substrate to form a film, and
The step of heat-treating the applied film
Containing polybenzimidazole membrane.
The method according to claim 6,
Wherein the second solution is allowed to stand at a temperature ranging from -20 占 폚 to 5 占 폚.
The method according to claim 6,
And the content of the second solution phase porogen is 30 to 55% by weight based on the total weight of the porous polybenzimidazole membrane.
The method according to claim 6,
Wherein the step of forming the film comprises applying a second solution on the substrate in a thickness of 100 to 250 탆.
The method according to claim 6,
Wherein the heat treatment is performed at a temperature ranging from 25 to 400 캜.

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