KR20080058139A - Polymer electrolyte membrane for fuel cell, manufacturing method thereof, and fuel cell employing the same - Google Patents

Abstract

A polymeric electrolyte membrane for a fuel cell is provided to maintain stabilized performance for a long term, and to produce a fuel cell having stabilized performance when the electrolyte membrane is applied to a membrane-electrode assembly. A method for manufacturing a polymeric electrolyte membrane for a fuel cell includes the steps of: adding a basic polymer and a polyfunctional crosslinking agent to an organic solvent, and appending the polyfunctional crosslinking agent to the basic polymer to obtain a polymer solution; crosslinking the basic polymer through a condensation reaction between the polyfunctional crosslinking agents to obtain a polymer membrane while removing the organic solvent from the polymer solution; and impregnating the polymer membrane with an acidic dopant at a temperature ranging from room temperature to 200 °C to obtain the polymer electrolyte membrane.

Description

Polymer electrolyte membrane for fuel cell, manufacturing method and fuel cell employing the same {Polymer electrolyte membrane for fuel cell, manufacturing method etc, and fuel cell employing the same}

1 is a perspective exploded view showing a main portion of a fuel cell according to the embodiment of the present invention;

FIG. 2 is a cross-sectional schematic diagram illustrating a membrane-electrode assembly provided in the fuel cell of FIG. 1.

3 is a view for explaining a method of performing the durability test, (a) is a graph showing the relationship between the output voltage and output current of the fuel cell and the operating time, (b) is the relationship between the open circuit voltage and the test time It is a graph showing an example.

[A brief description of the major signs]

One… . Fuel cell 10. Membrane-electrode assembly

20... Bipolar plate 100... Electrolyte Membrane (Polymer Electrolyte for Fuel Cell)

110, 110 '... Catalyst layer 120,120 ', 121,121'... Gas diffusion layer

The present invention relates to a polymer electrolyte membrane for a fuel cell, a method for manufacturing the same, and a fuel cell employing the same, and more particularly, to a fuel cell operating in a temperature range of 100 to 200 ° C. without providing a special fuel gas humidifier. A superior polymer electrolyte membrane, a method for producing the same, and a fuel cell employing the polymer electrolyte membrane are described.

Polymer electrolyte membranes used as solid polymer fuel cells are required to have high ion conductivity and excellent long-term stability. US Patent No. 5,525,436 discloses an electrolyte membrane in which polybenzimidazole membrane is doped with orthophosphoric acid. In addition, Japanese Patent Laid-Open No. 2000-281819 discloses an electrolyte membrane in which polybenzimidazole is crosslinked with a diepoxy compound or the like in order to improve the mechanical strength of the polymer membrane. In addition, Japanese Patent Publication No. 2005-535734 discloses an electrolyte membrane in which a polymer blend containing polybenzimidazole is crosslinked with a diepoxy compound or the like.

The techniques described in US Pat. No. 5,525,436, Japanese Patent Laid-Open No. 2000-281819, and Japanese Patent Laid-Open No. 2005-535734 are all impregnated with a basic polymer, polybenzimidazole, for impregnating a dopant represented by orthophosphoric acid. The membrane electrode assembly using the electrolyte membrane does not have sufficient long-term stability, and as described in Japanese Patent Laid-Open No. 2000-281819 or Japanese Patent Publication No. 2005-535734, the mechanical strength of the membrane is improved by the crosslinking agent, but still its characteristics This was insufficient.

It has been found that this kind of electrolyte membrane is caused by a large dimensional difference in the hygroscopic state and the dry state, because the long-term stability of the electrolyte membrane having the membrane strength improved by the crosslinking agent is not improved to a satisfactory level.

That is, the electrolyte membrane containing a large amount of acidic dopant is in a closed state in accordance with the generated water in the closed loop state, while in the open circuit state or low current density, the absorbed moisture is largely out of the electrolyte membrane, and becomes dry.

The change in the dimensions of the electrolyte membrane occurs due to the adsorption and desorption of moisture between the water-containing state and the dry state, and in particular, the tensile stress is generated in the electrolyte membrane having the end fixed in the cell by the dimension change in the planar direction. Conventionally, the tensile stress has been solved by a method of enhancing the yield strength or the breaking strength of the electrolyte membrane, but there is still much room for improvement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a polymer electrolyte membrane for a fuel cell, a method for manufacturing the same, and a fuel cell employing the same, which can maintain stable performance over a long period of time.

As a result of intensive studies by the present inventors to improve the long-term stability of the electrolyte membrane, the electrolyte membrane that transcends the range of the dimensional change in the water-containing state and the dry state has a long-term stable performance when fabricating a membrane electrode assembly using the same. I found it hard to keep up.

In more detail, in the actual stress-distortion test of most polymer membranes or electrolyte membranes, a yield point exists in the range of about 10% or less of elongation. Therefore, when the elongation is more than 5%, plastic deformation is already started. For this reason, when the dimensional change exceeds 5% in the planar direction in the hydrous state and in the dry state of the electrolyte membrane, many electrolyte membranes cause plastic deformation, which is likely to cause small cracks or breakage of the electrolyte membrane.

In addition, it is considered that the micro plastic deformation within one time does not affect the long-term durability of the electrolyte membrane very much. However, in the electrolyte membrane for fuel cell, since small plastic deformation may occur repeatedly depending on the operating conditions of the fuel cell, fatigue due to repetition of plastic deformation tends to accumulate, and in the long term, fracture or crossover of the membrane is extremely extreme. Is likely to increase.

As a result, when the rate of dimensional change between the aqueous state and the dry state of the electrolyte membrane exceeds 5%, it is difficult for the membrane electrode assembly using the same to maintain stable performance for a long term.

Based on this, in order to achieve the above object, the present invention adopts the following configuration.

The polymer electrolyte membrane for a fuel cell of the present invention is a polymer electrolyte membrane containing a basic polymer and an acidic dopant, and characterized in that the rate of dimensional change in the planar direction of the polymer electrolyte membrane from a hydrous state to a dry state is 5% or less.

In the fuel cell polymer electrolyte membrane of the present invention, it is preferable that the basic polymer contains polybenzimidazole or a derivative thereof.

Furthermore, in the polymer electrolyte membrane for fuel cells of the present invention, it is preferable that the basic polymer contains polybenzimidazole or a derivative thereof crosslinked by a reaction with a polyfunctional crosslinking agent.

Furthermore, in the polymer electrolyte membrane for fuel cells of the present invention, it is preferable that the basic polymer contains polybenzimidazole or a derivative thereof crosslinked with an epoxy group-containing alkoxysilane.

In the fuel cell polymer electrolyte membrane of the present invention, the acidic dopant is preferably phosphoric acid or organic phosphonic acid.

Next, the method for producing a polymer electrolyte membrane for a fuel cell of the present invention is a step of adding a basic polymer and a polyfunctional crosslinking agent to an organic solvent, and adding the polyfunctional crosslinking agent to the basic polymer to form a polymer solution, and the organic solution from the polymer solution. Removing the solvent and condensing the multifunctional crosslinking agents to crosslink the basic polymer to obtain a polymer membrane; and obtaining a polymer electrolyte membrane by impregnating an acid dopant in the polymer membrane under an environment of room temperature (20 ° C) to 200 ° C. It includes.

In addition, the method for producing a polymer electrolyte membrane for a fuel cell of the present invention is a step of adding a basic polymer and a polyfunctional crosslinking agent in an organic solvent, crosslinking the basic polymer with the polyfunctional crosslinking agent to a polymer solution, and the organic solution from the polymer solution The process of obtaining a polymer membrane by removing a solvent, and the process of obtaining a polymer electrolyte membrane by impregnating an acidic dopant with the said polymer membrane in the environment of room temperature to 200 degreeC are included.

Moreover, in the manufacturing method of the polymer electrolyte membrane for fuel cells of this invention, it is preferable that the said basic polymer is polybenzimidazole or its derivative (s), and the said polyfunctional crosslinking agent is an epoxy group containing alkoxysilane.

Moreover, in the manufacturing method of the polymer electrolyte membrane for fuel cells of this invention, it is preferable that the said basic polymer is polybenzimidazole or its derivative (s), and the said polyfunctional crosslinking agent is 1, 4- butanediol diglycidyl ether.

Subsequently, the fuel cell of the present invention comprises a pair of catalyst layers and an electrolyte membrane disposed between each catalyst layer, and the electrolyte membrane comprises the polymer electrolyte membrane for fuel cells described above.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described with reference to drawings. 1 is an exploded perspective view showing an example of a fuel cell of the present embodiment, and FIG. 2 is a cross-sectional schematic diagram of a membrane-electrode assembly constituting the fuel cell of FIG. 1.

In the fuel cell 1 shown in FIG. 1, two unit cells 11 are sandwiched by a pair of holders 12 and 12, and the structure is outlined. The unit cell 11 is composed of a membrane-electrode assembly 10 and bipolar plates 20 and 20 disposed on both sides of the membrane-electrode assembly 10 in the thickness direction. The bipolar plates 20 and 20 are made of a conductive metal, carbon, or the like, and are bonded to the membrane-electrode assembly 10 to function as a current collector and to the catalyst layer of the membrane-electrode assembly 10. Oxygen and fuel.

The number of unit cells 11 is two in the fuel cell 1 shown in FIG. 1, but the number of unit cells is not limited to two, and may be increased to several tens to hundreds depending on the characteristics required for the fuel cell. have.

As shown in FIG. 2, the membrane-electrode assembly 10 is disposed on both sides of the polymer electrolyte membrane for fuel cell (hereinafter referred to as electrolyte membrane) 100 and the thickness direction of the electrolyte membrane 100 according to the present invention. Catalyst layers 110 and 110 ', first gas diffusion layers 121 and 121' stacked on the catalyst layers 110 and 110 ', respectively, and second gas diffusion layers stacked on the first gas diffusion layers 121 and 121', respectively. 120 and 120 '.

The catalyst layers 110 and 110 'function as a fuel electrode and an oxygen electrode, and each includes a catalyst material such as activated carbon and a binder for solidifying the catalyst material. As the binder, a fluororesin excellent in heat resistance may be used, or a material constituting the electrolyte membrane according to the present invention may be used. By using the material constituting the electrolyte membrane as a binder, proton diffusion inside the catalyst layers 110 and 110 'is efficiently carried out, and the impedance of the catalyst layers 110 and 110' is lowered to improve the output of the fuel cell. In addition, as will be described later, the electrolyte membrane according to the present invention has a small dimensional change rate, so that the catalyst layers 110 and 110 'containing the constituent material of the electrolyte membrane have little shape change and are excellent in long-term stability.

The first gas diffusion layers 121 and 121 'and the second gas diffusion layers 120 and 120' are each formed of, for example, carbon sheets, and the catalyst layer is formed of oxygen and fuel supplied through the bipolar plates 20 and 20, respectively. Diffusion to the front of (110, 110 ').

The fuel cell 1 including the membrane-electrode assembly 10 operates at a temperature of 100 to 300 ° C., for example, hydrogen is supplied as fuel through the bipolar plate 20 to one catalyst layer side, and the other On the side of the catalyst layer, for example, oxygen is supplied as an oxidant through the bipolar plate 20. Hydrogen is oxidized in one catalyst layer to produce protons. The protons conduct the electrolyte membrane 4 to reach the other catalyst layer, and protons and oxygen react electrochemically in the other catalyst layer to generate water. At the same time, it generates electrical energy.

In addition, hydrogen supplied as a fuel may be hydrogen generated by the reforming of a hydrocarbon or alcohol, and oxygen supplied as an oxidant may be supplied in a state contained in air.

Next, the electrolyte membrane 100 provided in the membrane-electrode assembly 1 will be described.

The electrolyte membrane 100 according to the present invention contains at least one or more basic polymers and an acidic dopant, and exhibits a dimensional change rate of 5% or less in the planar direction of the membrane from a watery state to a dry state. Preferably, the dimensional change rate is more preferably 4% or less.

As a basic polymer which comprises an electrolyte membrane, polybenzimidazole or its derivative (s) or polybenzimidazole or its derivative (s) bridge | crosslinked by the polyfunctional crosslinking agent can be illustrated.

Polybenzimidazole or derivatives thereof (hereinafter referred to as "polybenzimidazoles") serve as the center of the electrolyte membrane according to the present invention, and the polybenzimidazoles maintain the shape of the electrolyte membrane in a constant shape. In the present invention, an electrolyte membrane is obtained by impregnating an acidic dopant with a membrane-like polybenzimidazole. Polybenzimidazoles are excellent in heat resistance and can be retained in a large amount when impregnated with an acidic dopant, and are suitable as constituents of the electrolyte membrane for fuel cells.

As polybenzimidazole which concerns on this invention, the polymer or its derivative (s) which has one of the structures represented by following General formula (1)-(d) can be illustrated.

 [Formula 1]

In (a)-(d) of the said Formula (1), n which shows the number of repeating structural units is 100-10000. In the formula (d), X is -O-, -SO _2- , -S-, -CO-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- 1 or more types selected are shown. If n is 10 or more, the mechanical strength of the polybenzimidazoles can be improved to constitute an electrolyte membrane excellent in strength. Thereby, the moldability of polybenzimidazoles improves, and the freedom degree of the shape of an electrolyte membrane becomes high. In addition, derivatives including one or more functional groups or functional groups selected from sulfonic acid groups and phosphonic acid groups may be bonded to the above formulas (a) to (d).

Polybenzimidazoles can be manufactured by a well-known technique. For example, the manufacturing method described in US Pat. No. 3,313,783, US Pat. No. 3,509,108, US Pat. No. 3,555,389, and the like are preferred.

The polybenzimidazoles described above are more preferably crosslinked with a polyfunctional crosslinking agent. As a polyfunctional crosslinking agent, 1, 4- butanediol diglycidyl ether and / or an epoxy group containing alkoxysilane are preferable, and an epoxy group containing alkoxysilane is especially preferable.

Among the said epoxy group containing alkoxysilanes, 3-glycidyl oxypropyl trimethoxysilane is especially preferable. These polyfunctional crosslinking agents have an epoxy group (glycidyl group) in a molecule | numerator, and this epoxy group couple | bonds with a basic polymer.

In the case of the polyfunctional group crosslinking agent provided with several epoxy group in a molecule | numerator, the main chains of adjacent polybenzimidazoles bond and crosslink.

In the case of an epoxy group-containing alkoxysilane having an epoxy group and an alkoxy group in the molecule, an epoxy group is added to the main chain of polybenzimidazoles to add an epoxy group-containing alkoxysilane to the main chain of polybenzimidazoles. Subsequently, by adding condensation reaction of the added epoxy group containing alkoxysilanes, the main chain of adjacent polybenzimidazoles finally bridge | crosslinks.

In addition, by using the silane compound as the crosslinking agent, the dimensional change rate can be made extremely small, and the heat resistance of the electrolyte membrane can be further increased.

The dimensional change rate in the planar direction of the electrolyte membrane of the present invention is more preferably 5% or less, particularly 4% or less, and in order to achieve a dimensional change rate of 4% or less, it is possible by a method of incorporating a polyfunctional crosslinking agent into the basic polymer.

It is preferable to use 1 or more types chosen from 1, 4- butanediol diglycidyl ether and an epoxy-group containing alkoxysilane as said polyfunctional crosslinking agent.

The blending ratio of the polyfunctional crosslinking agent to the polybenzimidazoles may be adjusted so that the rate of dimensional change in the planar direction of the electrolyte membrane from the hydrous state to the dry state can be 5% or less, preferably 4% or less.

The amount of the multifunctional crosslinking agent is preferably 3 to 11% by weight based on the total weight of the composition for forming a polymer membrane in consideration of the electrochemical performance of the electrolyte membrane.

When 1, 4- butanediol diglycidyl ether is used as a polyfunctional crosslinking agent, it is preferable that it is 3-11 weight% based on the total weight of the composition for polymer film formation. If the blending amount of the multifunctional crosslinking agent is less than 3% by weight, the rate of dimensional change is too large, and if it exceeds 11% by weight, the electrochemical performance of the electrolyte membrane is lowered, which is not preferable.

When using an epoxy-group containing alkoxysilane like 3-glycidyloxypropyl trimethoxysilane as a polyfunctional crosslinking agent, it is preferable that it is 3-7 weight%. If the blending amount of the multifunctional crosslinking agent is less than 3% by weight, the rate of dimensional change is too large, and if it exceeds 7% by weight, the electrochemical performance of the electrolyte membrane is lowered, which is not preferable.

Subsequently, it is preferable to use phosphoric acid or organic phosphonic acid for the acidic dopant. As phosphoric acid, metaphosphoric acid, orthophosphoric acid, paraphosphoric acid, triphosphoric acid, tetraphosphoric acid, etc. are preferable, for example, orthophosphoric acid is more preferable. Moreover, as organic phosphonic acid, alkyl phosphonic acids, such as methyl phosphonic acid, ethyl phosphonic acid, and propyl phosphonic acid, or vinyl phosphonic acid and phenyl phosphonic acid are preferable, and vinylphosphonic acid is more preferable among these, for example.

The impregnation rate (dope amount) of the polybenzimidazoles of these acidic dopants is preferably in the range of 20 mol% to 2000 mol% with respect to the repeating structural units of the polybenzimidazoles. The range is more preferable. If the impregnation rate of the acidic dopant is 20 mol% or more, the proton conductivity of the electrolyte membrane is sufficiently high, and when the electrolyte membrane is placed in a fuel cell, good power generation characteristics can be expressed. When the impregnation rate is 2000 mol% or less, the impregnation rate for the polybenzimidazoles does not become excessive, the polybenzimidazoles do not dissolve, and the proton conductivity can be stably maintained for a long time.

Next, the electrolyte membrane according to the present invention preferably has a dimensional change rate in the planar direction of the electrolyte membrane from the watery state to the dry state of 5% or less, more preferably 4% or less. If the rate of dimensional change is 5% or less, it becomes possible to keep the membrane electrode assembly performance stable in the long term. That is, when the dimensional change rate of the electrolyte membrane is 5% or less, plastic deformation does not occur while the electrolyte membrane changes from a water-containing state to a dry state, and minute cracks in the electrolyte membrane are prevented or breakage of the electrolyte membrane is prevented. In addition, even in a situation where the electrolyte membrane repeatedly causes small plastic deformation depending on the operation of the fuel cell, fatigue caused by repeated plastic deformation does not accumulate, and in the long run, it is possible to reduce the possibility of leading to extreme breakage of the membrane or crossover. It becomes possible.

There is no restriction | limiting in particular in the means which sets the rate of dimensional change of 5% or less in the planar direction in the electrolyte state and the dry state of electrolyte membrane. Considering the combination of the molecular structure of the basic polymer constituting the electrolyte membrane and the acidic dopant, the means can be selected within a range that does not impair various characteristics such as ionic conductivity and handleability of the finished electrolyte membrane.

For example, when using the basic polymer which introduce | transduced the crosslinked structure as a basic polymer, you may use the conventionally well-known 1, 4- butanediol diglycidyl ether etc. as a crosslinking agent. In this case, what is necessary is just to adjust within 5% of a dimensional change rate according to the kind of acidic dopant and processing temperature, and it can select from the range which does not impair various characteristics, such as ion conductivity and handleability.

Particularly in the present invention, in the case of using a basic polymer having a crosslinked structure, in consideration of the manufacturing process of the electrolyte membrane, the basic polymer is not crosslinked at once with a polyfunctional crosslinking agent, but the crosslinkability is imparted to the basic polymer. The basic polymer which introduce | transduced the crosslinking structure obtained by the two-step process of advancing crosslinking at the time of film forming can be used. In this case, a suitable example is a method in which an epoxy group-containing alkoxysilane is reacted with a basic polymer to impart crosslinking properties, and then a hydrolytic condensation reaction is introduced to introduce a crosslinked structure.

In addition, when using a non-crosslinked basic polymer, it is suitable to select a molecular structure having a relatively high planar orientation of the polymer chain, for example, a molecular structure in which a sulfone group or an ether group is introduced into a main chain or a phosphone group is introduced into a benzene ring. In this case, however, the acid dopant may be adjusted within 5% of the dimensional change rate according to the type and treatment temperature, and can be selected within a range that does not impair various characteristics such as ion conductivity and handleability.

Here, the electrolyte membrane in the water-containing state refers to an electrolyte membrane in which an acid dopant is impregnated with polybenzimidazoles crosslinked with a polybenzimidazole or a polyfunctional crosslinking agent and further impregnated with water. The electrolyte membrane in this state is swollen by the acidic dopant and water, and the dimension in the planar direction is largely adjusted.

On the other hand, an electrolyte membrane in a dry state refers to an electrolyte membrane in which an acidic dopant is impregnated with polybenzimidazoles or polybenzimidazoles crosslinked with a polyfunctional crosslinking agent and water is removed. The electrolyte membrane in such a state is swollen with an acidic dopant, and the dimension in the planar direction is smaller than that of the hydrous electrolyte membrane.

The electrolyte membrane in the water-containing state is obtained by, for example, impregnating orthophosphoric acid at a concentration of 85% by weight in polybenzimidazoles or polybenzimidazoles crosslinked with a polyfunctional crosslinking agent. Orthophosphoric acid at a concentration of 85% contains 15% of water, and this 15% by weight of water is impregnated with the orthophosphoric acid to the electrolyte membrane to become a water-containing state.

In addition, when power is generated by connecting an external load to the fuel cell, water generated by the power generation reaction is impregnated into the electrolyte membrane. The electrolyte membrane in this state is a water-containing state.

On the other hand, the dry electrolyte membrane is dried by, for example, vacuum drying the electrolyte membrane in the above water-containing state at 60 ° C for 24 hours under a reduced pressure of 1 mmHg or less.

In addition, when the external load is not connected to the fuel cell and the power generation current is almost 0 A, and the fuel gas such as hydrogen and the oxidizing gas such as oxygen (air) are in the state of distribution, the electrolyte membrane is dried by the fuel gas and the oxidizing gas And water in the electrolyte membrane is removed. The electrolyte membrane in this state is in a dry state.

Next, the manufacturing method of the electrolyte membrane which concerns on this invention is demonstrated. As described above, the electrolyte membrane according to the present invention is divided into a case of performing a crosslinking reaction in one step and a case of performing a crosslinking reaction in two steps.

In the case where the crosslinking reaction is carried out in one step, for example, it is preferable to use 1,4-butanediol diglycidyl ether as the polyfunctional crosslinking agent.

Specifically, first, a basic polymer and a polyfunctional crosslinking agent are added to an organic solvent to prepare a mixed solution. It is preferable to use polybenzimidazoles as a basic polymer, and it is preferable to use N, N- dimethyl acetamide, dimethylformamide, dimethyl sulfamide, N-methyl- 2-pyrrolidone, etc. as an organic solvent. . What is necessary is just to react a crosslinking reaction for 5 minutes-2 hours in the temperature range of 120-180 degreeC, after adding a basic polymer and a polyfunctional crosslinking agent in an organic solvent, for example.

Subsequently, when the mixed solution is heated to remove the organic solvent from the mixed solution, the crosslinking reaction may be performed at the same time, and the heating is allowed to react for 5 minutes to 2 hours in the temperature range of 120 to 180 ° C. By this process, a polymer membrane is obtained. Thereafter, an electrolyte membrane can be obtained by impregnating an acidic dopant in the polymer membrane under an environment of room temperature to 200 ° C.

When performing a crosslinking reaction in two steps, it is preferable to use an epoxy group containing alkoxysilane as a polyfunctional crosslinking agent, for example.

Specifically, first, a basic polymer and a polyfunctional crosslinking agent are added to an organic solvent, and a polyfunctional crosslinking agent is added to a basic polymer to make a polymer solution. At this time, in addition reaction, the epoxy group of an epoxy-group containing alkoxysilane ring-opens and an addition reaction with respect to a basic polymer arises. It is preferable to use polybenzimidazoles as a basic polymer, and it is preferable to use N, N- dimethyl acetamide, dimethylformamide, dimethyl sulfamide, N-methyl- 2-pyrrolidone, etc. as an organic solvent. . The addition reaction may be performed by, for example, adding a basic polymer and a polyfunctional crosslinking agent in an organic solvent and then reacting for 5 minutes to 2 hours at a temperature range of 50-80 ° C.

Subsequently, the organic solvent and the like are removed from the polymer solution after the addition reaction, and the polyfunctional crosslinking agents are condensed to crosslink the basic polymer to obtain a polymer film. The condensation reaction at this time is a condensation reaction in which an alkoxy group of an epoxy group-containing alkoxysilane condenses to form a siloxane bond. When removing an organic solvent, what is necessary is just to heat for 5 minutes-2 hours in 120-180 degreeC. By the said heating, the polyfunctional crosslinking agent added to a basic polymer causes condensation reaction, and a basic polymer crosslinks by this. In this way, a polymer film is obtained.

Thereafter, an electrolyte membrane is obtained by impregnating an acidic dopant in the polymer membrane under an environment of room temperature to 200 ° C.

As described above, according to the electrolyte membrane described above, since the rate of dimensional change is 5% or less, plastic deformation does not occur while the electrolyte membrane changes from a water-containing state to a dry state, and microcracks in the electrolyte membrane occur or Breaking can be prevented. In addition, even when the electrolyte membrane repeatedly causes minute plastic deformation depending on the operation of the fuel cell, fatigue caused by repeated plastic deformation does not accumulate, and in the long run, it is possible to reduce the possibility of leading to extreme breakage of the membrane or crossover. have.

EXAMPLE

Various electrolyte membranes were prepared, the dimensional change rate of the electrolyte membrane was obtained, and the durability test of the electrolyte membrane was performed. The measuring method of a dimensional change rate and the implementation method of an endurance test are as follows.

`` Measurement method of size change rate ''

The basic polymer is immersed in an acidic dopant selected in consideration of ionic conductivity, handleability, and the like to prepare an electrolyte membrane composed of the basic polymer and the acidic dopant. The treatment conditions at this time are selected in consideration of ion conductivity, handleability and the like. For example, in the case of impregnating orthophosphoric acid, the liquid temperature may be maintained at about room temperature to 60 ° C., and the immersion time may be adjusted to the time until the impregnation rate of the acid dopant becomes constant. The obtained electrolyte membrane is an electrolyte membrane in a hydrous state. The excess acid is wiped away from the electrolyte membrane, the membrane is measured in two plane directions, and then vacuum dried at 60 ° C for 24 hours to remove moisture. The electrolyte membrane at this time is an electrolyte membrane in a dry state. Then, the dimensional change rate in the planar two directions of the electrolyte membrane between the water-containing state and the dry state is determined, respectively, and the average value is taken as the dimensional change rate.

`` Durability test method of electrolyte membrane ''

A commercially available gas diffusion electrode is bonded to the prepared electrolyte membrane to prepare a membrane electrode assembly having an effective area of 25 cm ² . This is put into a fuel cell evaluation cell, and power generation operation is performed with hydrogen / air. At this time, the operating temperature is 150 ° C., and the gas utilization rate is constant operation of 80% hydrogen and 50% air at a current density of 0.2 A / cm ² or more, and at a constant flow rate operation of 0.2 A / cm ^{2 at a} lower level. do.

In order to bring the electrolyte membrane closer to the dry state, the electrolyte membrane is left to operate in an open circuit state. In addition, in order to make it into a water-containing state, operation is performed with a current density of 0.6-1 A / cm <^2> as an upper limit current density. As a method of repeatedly changing from a dry state to a water-containing state, it is repeated to change a current value to an upper limit current density after leaving it for a predetermined time in an open-circuit state. In order to suppress the effect of the change as much as possible for about 10 minutes, the current scan is performed for about 40 minutes to 60 minutes up to the upper limit current density in order to exclude the effect of gas supply shortage due to a sudden change in the current value. . The relationship between the output voltage and output current of a fuel cell, and an operation time is shown to FIG. 3 (a). The durability test of this example is performed by repeating the pattern shown to Fig.3 (a). 3A, the solid line plots the output voltage and the dotted line plots the output current.

As the durability evaluation method, the time at which the open circuit voltage starts to drop rapidly is regarded as the endurance time in the relationship between the open circuit voltage obtained by the current scan and the operation time. The test time is up to 1000 hours and the test is stopped at 1000 hours. An example of the relationship between the open circuit voltage and the test time is shown graphically in FIG. FIG. 3B is a graph showing an example in which the open-circuit voltage starts to drop rapidly in about 240 hours.

"Example 1"

According to the following procedure, an electrolyte membrane was prepared in which polybenzimidazoles crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent were impregnated with 400% by weight of orthophosphoric acid.

Specifically, N, N-diacetamide solution in which 10% by weight of poly-2,2 '-(m-phenylene) -5,5'-bibenzimidazole represented by Formula (a) is dissolved. To 5 parts by weight of 1,4-butanediol diglycidyl ether was added to make a mixed solution.

The mixed solution thus obtained was cast on a glass substrate and heated at 150 ° C. for 5 hours to remove the organic solvent and to advance the crosslinking reaction. In this way, a polymer membrane was produced.

The obtained polymer membrane was impregnated with orthophosphoric acid having a purity of 85% by weight at room temperature for 1 hour. Thus, the electrolyte membrane of Example 1 was prepared.

The dimensional change rate was 4% about the obtained electrolyte membrane. Moreover, as a result of the endurance test, the endurance time was 750 hours.

"Example 2"

According to the following procedure, an electrolyte membrane was prepared in which polybenzimidazoles crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent were impregnated with 120% by weight of ethylphosphonic acid.

Specifically, N, N-diacetamide solution in which 10% by weight of poly-2,2 '-(m-phenylene) -5,5'-bibenzimidazole represented by Formula (a) is dissolved. To 10 parts by weight of 1,4-butanediol diglycidyl ether was added to make a mixed solution.

The mixed solution was cast on a glass substrate and heated at 150 ° C. for 5 hours to remove the organic solvent and to advance the crosslinking reaction. In this way, a polymer membrane was produced.

The obtained polymer membrane was impregnated with ethylphosphonic acid having a purity of 85% by weight heated to a temperature of 120 ° C for 5 hours. In this way, the electrolyte membrane of Example 2 was manufactured.

About the obtained electrolyte membrane, the dimensional change rate was 0%. In addition, the endurance test showed that the endurance time was 950 hours.

"Example 3"

According to the following procedure, an electrolyte membrane was prepared in which polybenzimidazoles were impregnated with 210% by weight of vinylphosphonic acid.

The polybenzimidazoles represented by the following formula (e) were dissolved in N, N-diacetamide to obtain a polymer solution having a concentration of 10% by weight, and the obtained polymer solution was cast on a glass substrate, The organic solvent was removed by heating on the conditions of 5 hours. In this way, a polymer membrane was produced.

[Formula 2]

In the formula, n was 340.

The polymer membrane obtained was impregnated with vinylphosphonic acid having a purity of 85% by weight and heated to a temperature of 120 ° C for 1 hour. Thus, the electrolyte membrane of Example 3 was prepared.

About the obtained electrolyte membrane, the rate of dimensional change was measured and found to be 2% of dimensional change. Moreover, as a result of the endurance test, the endurance time was 800 hours.

"Example 4"

According to the following procedure, an electrolyte membrane was prepared in which benzimidazoles were impregnated with 100% by weight of ethylphosphonic acid.

Specifically, 10 parts by weight of 1,4-butanediol diglycidyl ether in an N, N-diacetamide solution in which 10% by weight of poly-2,5-benzimidazole represented by Formula (c) is dissolved. Was added to make a mixed solution. This mixed solution was cast on a glass substrate, and the crosslinking reaction was advanced while removing an organic solvent by heating on 150 degreeC and the conditions of 5 hours. In this way, a polymer membrane was produced.

The obtained polymer membrane was impregnated with ethylphosphonic acid having a purity of 85% by weight heated to a temperature of 120 ° C for 5 hours. Thus, the electrolyte membrane of Example 4 was prepared.

The dimensional change rate was measured about the obtained electrolyte membrane, and the dimensional change rate was 0%. Moreover, as a result of the endurance test, the endurance time was 1000 hours or more.

"Example 5"

According to the following procedure, an electrolyte membrane was prepared in which polybenzimidazoles cross-linked 3-glycidyl oxypropyl trimethoxysilane as a crosslinking agent were impregnated with 150% by weight of orthophosphoric acid.

Specifically, 5 parts by weight of 3-glycidyl oxypropyl trimethoxysilane was added to an N, N-diacetamide solution in which 10% by weight of the polybenzimidazoles represented by the formula (3) Made of mixed solution.

The mixed solution was reacted by addition at 80 ° C. for 2 hours to form a polymer solution. The obtained polymer solution was cast on the glass substrate, and the organic solvent was removed, heating to 150 degreeC and the conditions for 5 hours, causing a hydrolysis polycondensation reaction. In this way, a polymer membrane was produced.

[Formula 3]

In the formula, n was 340.

The obtained polymer membrane was impregnated with orthophosphoric acid having a purity of 85% by weight at room temperature for 1 hour. Thus, the electrolyte membrane of Example 5 was prepared.

The dimensional change rate was measured about the obtained electrolyte membrane, and the dimensional change rate was 1%. Moreover, as a result of the endurance test, the endurance time was 900 hours.

"Example 6"

According to the following procedure, an electrolyte membrane was prepared in which polybenzimidazoles were impregnated with 210% by weight of vinylphosphonic acid.

Specifically, polybenzimidazoles represented by (g) of the following formula (4) are dissolved in N, N-diacetamide to make a polymer solution having a concentration of 10% by weight, and the obtained polymer solution is cast on a glass substrate, The organic solvent was removed by heating on 150 degreeC and the conditions of 5 hours. In this way, a polymer membrane was produced.

[Formula 4]

In the formula, n was 180.

The obtained polymer membrane was impregnated with vinylphosphonic acid having a purity of 85% and heated at a temperature of 120 ° C for 1 hour. Thus, the electrolyte membrane of Example 6 was prepared.

The dimensional change rate was measured about the obtained electrolyte membrane, and the dimensional change rate was 1%. Moreover, the endurance test showed that the endurance time was 850 hours.

`` Comparative Example 1 ''

According to the following procedure, an electrolyte membrane including 350 wt% orthophosphoric acid was impregnated into polybenzimidazoles was prepared.

Specifically, poly-2,2 '-(m-phenylene) -5,5'-bibenzimidazole represented by Formula (a) of Formula 1 was dissolved in N, N-diacetamide to have a concentration of 10% by weight. The organic solvent was removed by making the polymer solution of%, cast the obtained polymer solution on a glass substrate, and heating at 150 degreeC and the conditions for 5 hours. In this way, a polymer membrane was produced.

The obtained polymer membrane was impregnated with orthophosphoric acid having a purity of 85% by weight at room temperature for 1 hour. Thus, the electrolyte membrane of Comparative Example 1 was prepared.

The dimensional change rate was measured about the obtained electrolyte membrane, and it was 10%. Moreover, as a result of the endurance test, the endurance time was 300 hours.

`` Comparative Example 2 ''

According to the following procedure, an electrolyte membrane was prepared in which polybenzimidazoles crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent were impregnated with 320% by weight of orthophosphoric acid.

Specifically, N, N-diacetamide solution in which 10% by weight of poly-2,2 '-(m-phenylene) -5,5'-bibenzimidazole represented by Formula (a) is dissolved To 2 parts by weight of 1,4-butanediol diglycidyl ether was added to make a mixed solution.

The mixed solution thus obtained was cast on a glass substrate and heated at 150 ° C. for 5 hours to remove the organic solvent and to advance the crosslinking reaction. In this way, a polymer membrane was produced.

The obtained polymer membrane was impregnated with orthophosphoric acid having a purity of 85% at room temperature for 1 hour. Thus, the electrolyte membrane of Comparative Example 2 was prepared.

The dimensional change rate was measured about the obtained electrolyte membrane, and it was 7%. Moreover, as a result of the endurance test, the endurance time was 450 hours.

`` Comparative Example 3 ''

According to the following procedure, an electrolyte membrane including 150 wt% orthophosphoric acid was impregnated into polybenzimidazoles was prepared.

Specifically, polybenzimidazoles represented by the formula (5) below are dissolved in N, N-diacetamide to obtain a polymer solution having a concentration of 10% by weight, and the obtained polymer solution is cast on a glass substrate. The organic solvent was removed by heating on 150 degreeC and the conditions of 2 hours. In this way, a polymer membrane was produced.

[Formula 5]

In the formula, n was 340. The obtained polymer membrane was impregnated with 85% by weight of orthophosphoric acid at room temperature for 1 hour. Thus, the electrolyte membrane of Comparative Example 3 was prepared.

The dimensional change rate was measured about the obtained electrolyte membrane, and it was 9%. Moreover, as a result of the endurance test, the endurance time was 200 hours.

According to the present invention, there is provided a polymer electrolyte membrane for a fuel cell which can maintain a stable performance for a long term, and when producing a membrane electrode assembly using the polymer electrolyte membrane, a fuel cell that can maintain a stable performance for a long term can be manufactured. have.

Claims (10)

A polymer electrolyte membrane comprising a basic polymer and an acidic dopant, wherein the rate of dimensional change in the planar direction of the polymer electrolyte membrane in a hydrous state and in a dry state is 5% or less. The polymer electrolyte membrane for a fuel cell according to claim 1, wherein the basic polymer comprises polybenzimidazole or a derivative thereof. The method of claim 1, wherein the basic polymer, A polymer electrolyte membrane for a fuel cell, comprising polybenzimidazole or a derivative thereof crosslinked by a reaction with a polyfunctional crosslinking agent. The polymer electrolyte membrane for a fuel cell according to claim 1, wherein the basic polymer comprises polybenzimidazole or a derivative thereof crosslinked with an epoxy group-containing alkoxysilane. The polymer electrolyte membrane for a fuel cell of claim 1, wherein the acidic dopant is phosphoric acid or organic phosphonic acid. Adding a basic polymer and a polyfunctional crosslinking agent to an organic solvent, and adding the polyfunctional crosslinking agent to the basic polymer to obtain a polymer solution; Performing a condensation reaction between the multifunctional crosslinkers while removing the organic solvent from the polymer solution to crosslink the basic polymer to obtain a polymer film; And A method of manufacturing a polymer electrolyte membrane for a fuel cell, comprising the step of obtaining a polymer electrolyte membrane by impregnating an acidic dopant in the polymer membrane at room temperature to 200 ° C. The method for producing a polymer electrolyte membrane for a fuel cell according to claim 6, wherein the basic polymer is polybenzimidazole or a derivative thereof, and the polyfunctional crosslinking agent is an epoxy group-containing alkoxysilane. Adding a basic polymer and a polyfunctional crosslinking agent in an organic solvent, and crosslinking the basic polymer with the polyfunctional crosslinking agent to obtain a polymer solution; Obtaining a polymer film by removing the organic solvent from the polymer solution; And A method of manufacturing a polymer electrolyte membrane for a fuel cell, comprising the step of obtaining a polymer electrolyte membrane by impregnating an acidic dopant in the polymer membrane at room temperature to 200 ° C. The method for producing a polymer electrolyte membrane for a fuel cell according to claim 8, wherein the basic polymer is polybenzimidazole or a derivative thereof, and the polyfunctional crosslinking agent is 1,4-butanediol diglycidyl ether. A pair of catalyst layers and an electrolyte membrane disposed between the catalyst layers, The fuel cell is a fuel cell polymer electrolyte membrane according to any one of claims 1 to 5.

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