JPH05242898A - Solid high polymer electrolyte for fuel cell - Google Patents

Abstract

PURPOSE:To provide a solid high polymer electrolyte excellent in heat resistance applicable to a fuel cell. CONSTITUTION:A high polymer matrix having a proton donating substituent while having heat-resisting aromatic group fluorinated polymer as a main component is made to dissociate the proton donating substituent or is made to be impregnated with a liquid midium which is proton-conductive itself in order to form a solid high polymer electrolyte. There are polyimide having a proton donating substituent and one or more fluorine.fluorine-containing substituent for examples as the heat-resisting aromatic group fluorinated polymer. A phosphoric acid/water mixed solution having phosphoric acid weight concentration 50% or more is the liquid midium as a suitable example.

Description

Detailed Description of the Invention

[0001]

The present invention can be applied to a fuel cell,
The present invention relates to a solid polymer electrolyte having excellent heat resistance.

[0002]

2. Description of the Related Art A fuel cell is an energy conversion device characterized by high efficiency, cleanliness, and compactness, and vigorous research and development has been conducted as a future power supply source. A single cell of a fuel cell is composed of a hydrogen electrode, an oxygen electrode, an electrolyte, and accessory parts. Depending on the type of the electrolyte, there are phosphoric acid type, inorganic oxide solid electrolyte type, polymer solid electrolyte type, molten salt type, and alkaline type. being classified. The alkaline type has a drawback that its performance is deteriorated by being contaminated with carbon dioxide contained in hydrogen gas as a raw material. The inorganic oxide solid electrolyte type and the molten salt type have high operating temperatures of 600 ° C. or higher and 900 ° C. or higher, respectively, and the thermal stress control based on the durability of the electrode material / structural material and the difference in the coefficient of thermal expansion of the material used. I have a problem. The phosphoric acid type has a limitation in its compactness and has a drawback that the power output density cannot be increased. On the other hand, the solid polymer electrolyte type has been developed mainly for artificial satellites and has been considered as a small-scale power source. As an electrolyte material, a proton-donating polymer having an alkyl fluoride main chain has excellent characteristics from the viewpoint of durability, and Nafion (trade name) manufactured by DuPont, USA
Are commercially available. This fluorinated alkyl polymer solid electrolyte has a high ionic conductivity, and has a concentration of 0.1 to 0.2S.
/ Cm ion conductivity has been realized, and high power density fuel cells have been prototyped [Journal of Power Sources, Vol. 29, 239.
Pp. 250 (1987)].

However, the current solid polymer electrolyte fuel cells have the drawback that a small amount of carbon monoxide contained in hydrogen gas as a fuel causes a decrease in the performance of the cell. Fuels are often produced by reforming hydrocarbons or methanol, and a trace amount of carbon monoxide contained therein is adsorbed by platinum of the electrode catalyst to become a catalyst poison. This deterioration in performance is caused by raising the operating temperature (80 to 100 ° C.) of the polymer electrolyte fuel cell, preferably 150 ° C.
Although the temperature can be reduced by raising the temperature as described above, since the conventional solid polymer electrolyte is impregnated with water as the ion conductive medium, the temperature cannot be raised to 100 ° C. or higher due to the evaporation of water. In addition, the fluoroalkyl polymer electrolyte has the drawback that it is softened at 150 ° C. or higher, the mechanical strength is lowered, and the continuous ion conductive phase is destroyed.

[0004]

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 solid electrolyte having excellent heat resistance which can be applied to a fuel cell.

[0005]

Briefly, the present invention relates to a polymer solid electrolyte for a fuel cell, which has a proton-donating substituent and a heat-resistant aromatic system having a glass transition point of 150 ° C. or higher. Dissociating the proton-donating substituent to a polymer matrix containing a fluorinated polymer as a main component,
Alternatively, it is characterized by being impregnated with a liquid medium which itself is proton conductive.

The inventors of the present invention have studied various existing solid polymer electrolyte fuel cells and solid polymer electrolytes, and as a result, in order to reduce the poisoning of the electrode catalyst (platinum), It became clear that the use temperature of the solid electrolyte must be 150 ° C. or higher.

In the polymer solid electrolyte of the present invention, the proton donating substituent forms an aggregate phase in the polymer constituting the polymer matrix, and the proton donating substituent is dissociated into this aggregate phase or by itself. Are impregnated with a liquid medium that is proton conductive to form an ion conductive phase. In this ionic conduction phase, the liquid medium having a high dielectric constant coordinates with the proton-donating substituent to dissociate the protons or release the protons themselves, and the protons move to develop ionic conductivity. Moreover, in the solid polymer electrolyte of the present invention, the polymer matrix that maintains the mechanical strength of the solid polymer electrolyte is 1
150 ° C because it has a glass transition temperature of 50 ° C or higher
Even with the above, it does not soften so much that it becomes a problem in use. Further, since the polymer main chain has an aromatic heat-resistant structure, deterioration due to thermal decomposition can be reduced. Further, since the polymer structure contains a fluorine substituent, the surface energy is lowered and the ion conductive phase can be stably maintained.

The main component of the polymer used in the polymer matrix of the present invention has a heat-resistant structure containing at least one aromatic ring in the main chain, and the aromatic ring is composed of a monocyclic ring such as a phenylene group or a naphthalene group. It may be a ring, and these aromatic rings may be substituted with a halogen, an alkyl group, a halogenated alkyl group or the like. Further, a hetero heterocycle such as benzimidazole may be used, and a phthalic imide structure is preferable because it has particularly excellent heat resistance. Therefore, the heat-resistant aromatic fluorinated polymer has the following general formula (Formula 1):

[0009]

[Chemical 1]

[In the formula, X represents a tetravalent organic group, Y represents a divalent organic group, and one or both of X and Y have at least one proton-donating substituent and at least one fluorine-containing group. A polyimide containing a repeating unit represented by "having one or both of fluorine substituents" is preferable.

The fluorine substituent may be directly bonded to the aromatic ring of the main chain or the side chain, or may be introduced into the main chain or the side chain in the form of a fluorinated alkyl group, a fluorinated alkenyl group or the like. .. In addition, an amide group, an ester group, an ether group,
It may contain a carbonate group, a sulfide group, a sulfone group or the like.

Examples of the proton donating substituent include a phenolic hydroxyl group, a sulfonic acid group, a carboxylic acid group and a phosphoric acid group.

The liquid medium which dissociates the proton-donating substituent to be impregnated or which is itself proton-conductive may be an acid or an aqueous solution containing a high concentration of an acid or a salt, but the phosphoric acid weight concentration is 50%. The above phosphoric acid / water mixed solution is particularly preferably used. Further, in order to sufficiently dissociate the proton-donating substituent, the relative permittivity thereof is preferably 20 or more.

The polymer matrix sheet may be produced by casting and heating a polymer solution on a substrate, or may be formed by heating and melting a raw material polymer and then pressing it.

The impregnation of the high dielectric constant liquid medium may be carried out by an ordinary method, for example, by immersing the polymer matrix sheet in the liquid medium. The impregnation amount of the liquid medium can be controlled by the length of the immersion time, but it is preferable to impregnate it with 10% by weight or more in the polymer electrolyte. The impregnation temperature is preferably raised to 150 ° C or higher.

[0016]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited thereto.

Example 1 4.44 g of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane 66 g was placed in 30 g of N-methyl-2-pyrrolidone (NMP), and 15 at room temperature under a nitrogen atmosphere.
I stirred it for a while. Subsequently, 40 ml of p-xylene was added to this solution, and the mixture was refluxed at 180 ° C. for 4 hours in a flask equipped with a reflux condenser with a moisture collector. 0.41 during this time
g water was collected. After distilling off p-xylene, the solution was cooled to room temperature, and this solution was added dropwise to 2 liters of water. The white solid deposited was filtered, washed with water and then vacuum dried at 100 ° C. to obtain a polymer matrix raw material. The glass transition temperature of this polymer was 303 ° C., and the thermal decomposition temperature (thermogravimetric analysis, temperature rising rate 10 ° C./min measurement) was 501 ° C. This polymer was again dissolved in NMP to prepare a 15 wt% solution, cast in a glass petri dish, dried at 190 ° C. for 5 hours and then vacuum dried at 200 ° C. for 3 hours to obtain a polymer matrix sheet. It was

A phosphoric acid / water mixed solution having a phosphoric acid weight concentration of 85% was prepared as a liquid medium which dissociates the proton-donating substituent or is itself proton-conductive. The prepared polymer matrix sheet is dipped in this, and 150
Impregnation was carried out at 0 ° C. for 3 hours to obtain a target polymer solid electrolyte sheet. When the measurement cell consisting of the produced solid polymer electrolyte and two platinum electrodes was assembled and the ionic conductivity was measured by the AC complex impedance method, it was 7 × 10 ^-2 S / cm (150
℃). The electrolyte was allowed to stand for 500 hours at 150 ° C. in a closed container in an oxygen atmosphere, and the ionic conductivity was measured again. As a result, it was 5 × 10 ⁻² S / cm (150 ° C.).

Comparative Example 1 After immersing Nafion 119 (trade name) manufactured by DuPont at room temperature in water for 1 day and measuring the ionic conductivity at 150 ° C., most of the water was evaporated and the ionic conductivity was high. Was 1 × 10 ⁻⁷ S / cm or less.

[0020]

As is apparent from the above description, the present invention has an advantage that a polymer solid electrolyte having excellent heat resistance, which can be applied to a fuel cell, can be obtained.

Claims (3)

[Claims] 1. A proton-donating substituent is dissociated in a polymer matrix having a proton-donating substituent and having a glass transition point of 150 ° C. or higher as a main component of a heat-resistant aromatic fluorinated polymer. Alternatively, a polymer solid electrolyte for a fuel cell, characterized in that it is impregnated with a liquid medium which is itself proton conductive. 2. The heat-resistant aromatic fluorinated polymer,
The following general formula (Formula 1): [In the formula, X represents a tetravalent organic group, Y represents a divalent organic group,
A polyimide having a repeating unit represented by one or both of X and Y having one or more proton donating substituents and one or more of one or more fluorine / fluorine-containing substituents. A polymer solid electrolyte for a fuel cell as described above. 3. The polymer solid electrolyte for a fuel cell according to claim 1, wherein the liquid medium is a phosphoric acid / water mixed solution having a phosphoric acid weight concentration of 50% or more.