JP2005302592A - Electrolyte film and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte film with a high temperature resistant property, free from swelling caused by a wet state thereof or damage generated by shrinkage caused by dry-up thereof. <P>SOLUTION: As for the electrolyte film used for a solid polymer electrolyte fuel cell having a thickness of 10 to 100 μm, a distortion up to a breaking point at tensile test is 15% or larger, and a glass transition temperature is 130°C or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolyte membrane that is used in a solid polymer electrolyte fuel cell and has high heat resistance and is not easily damaged by swelling, and a fuel cell using the electrolyte membrane.

  A unit cell, which is the minimum power generation unit of a solid polymer electrolyte fuel cell, generally has a membrane electrode assembly in which a catalyst electrode layer is bonded to both sides of an electrolyte membrane, and gas diffusion is performed on both sides of the membrane electrode complex. Layers are arranged. Furthermore, a separator having a gas flow path is arranged outside thereof, and the fuel gas and the oxidant gas supplied to the catalyst electrode layer of the membrane electrode composite are passed through the gas diffusion layer, It works to transmit the current obtained by power generation to the outside.

  In conventional solid polymer electrolyte fuel cells, for example, a resin having a relatively low glass transition temperature such as perfluorosulfonic acid resin is often used for the electrolyte membrane. However, the upper limit of the operable temperature of these electrolyte membranes is about 80 ° C. due to the low glass transition temperature. Therefore, a fuel cell that can be operated at a higher temperature for use in automobiles and the like, in particular, a general-purpose radiator temperature of about 120 ° C. is desired, and a material having a high glass transition temperature that enables this is used. An electrolyte membrane has been proposed.

  In addition, the solid electrolyte membrane in such a fuel cell has the property of causing dimensional expansion or dimensional shrinkage due to its wet state. That is, the solid electrolyte membrane expands in size as the water content increases, and shrinks in size as the water content decreases. Such a dimensional change is a strain of about 15% as compared with the electrolyte membrane during drying. However, a material having a high glass transition temperature such as an engineering plastic is generally a brittle material. The characteristics do not change even when proton conductors are formed by applying the above. Therefore, when such a fragile material is used as the electrolyte membrane, the electrolyte membrane is easily broken due to a dimensional change caused by repeated swelling and drying in the fuel cell.

  Patent Document 1 proposes an electrolyte membrane composed of a three-dimensional skeleton made of a crosslinked polymer and a carbon fluoride electrolyte reinforced by the three-dimensional skeleton. However, this is for the purpose of reducing the thickness of the electrolyte membrane for improving the controllability of the water content in the fuel cell, and the three-dimensional framework improves the mechanical strength of the fluorocarbon material. Is. Further, since a fluorine-based carbon material is used for the electrolyte membrane, it cannot withstand use at high temperatures.

JP 10-340732 A

  The present invention has been made in view of the above problems, and provides an electrolyte membrane that has high heat resistance and is free from problems such as swelling due to wetness of the electrolyte membrane and damage to the electrolyte membrane caused by shrinkage due to drying. Is the main purpose.

  In order to achieve the above object, the present invention provides an electrolyte membrane used in a solid polymer electrolyte fuel cell, wherein the strain up to the yield point by a tensile test of the electrolyte membrane having a thickness of 10 to 100 μm is 15% or more. The electrolyte membrane is characterized in that the glass transition temperature of the electrolyte membrane is 130 ° C. or higher.

  In the electrolyte membrane of the present invention, since the strain up to the yield point is within the above range, even when the electrolyte membrane swells in a wet state, it is possible to prevent a problem that the electrolyte membrane is damaged due to a change in its shape. Further, since the electrolyte membrane of the present invention has a glass transition temperature of 130 ° C. or higher, it can be used at a higher temperature than the conventional one.

In the said invention, it is preferable that the density of the said electrolyte membrane is 1.9 or less.
In addition, the present invention provides a membrane electrode assembly using the above electrolyte membrane. By using the electrolyte membrane in a membrane electrode assembly, a membrane electrode assembly with good durability that can be used at high temperatures and that does not damage the electrolyte membrane due to swelling can be obtained.

  The present invention further provides a fuel cell using the above electrolyte membrane. By using the electrolyte membrane in a fuel cell, it is possible to obtain a fuel cell with good durability that can operate the fuel cell at a high temperature and does not damage the electrolyte membrane due to swelling. .

  The present invention can be used at a high temperature, and even when the electrolyte membrane repeatedly expands due to swelling due to water absorption or shrinks due to drying, it is possible to reduce problems such as damage due to changes in its shape. There is an effect.

Hereinafter, the electrolyte membrane, membrane electrode assembly, and fuel cell of the present invention will be described in detail.
A. Electrolyte membrane First, the electrolyte membrane of the present invention will be described.
The electrolyte membrane of the present invention is an electrolyte membrane used for a solid polymer electrolyte fuel cell, and has a strain up to a yield point by a tensile test of the electrolyte membrane having a thickness of 10 to 100 μm of 15% or more. The glass transition temperature is 130 ° C. or higher.

  In order to enable operation at higher temperatures in a fuel cell, it is necessary to improve the heat resistance of the electrolyte membrane. For this purpose, it is effective to use a material having a high glass transition temperature (hereinafter sometimes referred to as “Tg”) as a material for forming the electrolyte membrane. Since the strain area that can be elastically deformed (hereinafter, this area may be referred to as “strain up to the yield point”) is small, cracks may occur due to repeated drying and wetting and may be damaged. high. Therefore, the present invention intends to prevent damage due to dimensional change due to swelling or the like by increasing the strain up to the yield point of the electrolyte membrane.

  The electrolyte membrane having the above characteristics can be used at a high temperature without being damaged by the dimensional change due to swelling. In general, since the dimensional change of the electrolyte membrane due to swelling in a wet state is below the above range, by setting the strain up to the yield point by the tensile test of the electrolyte membrane within the above range, the electrolyte membrane is damaged more than the dimensional change due to swelling, etc. Can be prevented.

  In the present invention, the strain up to the yield point refers to the time until the yield point is reached when a tensile test is performed at a temperature of 95 ° C. and a tensile rate of 10 mm / min using the specimen type 5 of JISK-7127 as a sample. The magnitude of the strain is expressed as a ratio (%) to the dimension before the tensile test.

  In the present invention, the strain to the yield point of the electrolyte membrane having a thickness of 10 to 100 μm, measured by the above method, is preferably 15% or more, and more preferably 25% or more. This is because by making the strain up to the yield point of the electrolyte membrane within the above range, a change in dimensions due to swelling or the like can be allowed without damage to the electrolyte membrane.

  In the present invention, Tg means that a sample on a strip having a width of 5 mm is sandwiched by 25 mm between chucks, the temperature is increased from room temperature to 200 ° C. at a temperature rising rate of 5 ° C./min, and the sample moves under tension at a frequency of 10 Hz. The viscoelasticity is measured and the temperature of the peak of the loss coefficient (Tanδ), which is the ratio between the storage elastic modulus and the loss elastic modulus, is measured.

  In the present invention, the Tg of the electrolyte membrane measured by the above method is preferably 130 ° C. or higher, more preferably 150 ° C. or higher. This is because by setting the Tg of the electrolyte membrane within the above range, the electrolyte membrane can be used at a high temperature, and the temperature range in which the fuel cell can operate can be widened.

  As a method of obtaining an electrolyte membrane having a strain up to a yield point within the above range and a Tg within the above range, by introducing a side chain into a material having a high Tg or adding a plasticizer, Examples include a method of inhibiting crystallinity and reducing Tg. In general, a material having a large strain up to the yield point tends to have a low Tg. By utilizing this characteristic and reducing the Tg by inhibiting the cohesive force and crystallinity of a material having a high Tg, it is possible to ensure the magnitude of strain up to the yield point required for the electrolyte membrane. For example, the polyether ether ketone represented by the following chemical formula (1) has a glass transition temperature of about 160 ° C., but as shown in the following chemical formula (2), by adding eight methyl groups to the side chain, the glass transition temperature It is estimated that the temperature drops to 150 ° C. and the strain to the yield point increases.

  The material used in this case is not particularly limited as long as it has a Tg of 130 ° C. or higher and can be converted into a proton conductor by adding a sulfonic acid group or the like, but polyacrylate (Tg 170 ° C.), Polyetherketone (Tg160 ° C), polyetheretherketone (Tg160 ° C), polyimide (Tg260 ° C), polyamideimide (Tg250 ° C), polyetherimide (Tg220 ° C), polyethersulfone (Tg220 ° C), and the like A hydrocarbon material of a combination of materials is preferably used.

  Among these, materials having a Tg of 200 ° C. or lower, such as polyacrylate (Tg 170 ° C.), polyether ketone (Tg 160 ° C.), and polyether ether ketone (Tg 160 ° C.) are more preferably used because of the relationship between the yield point and Tg. . In addition, when using a material having a Tg exceeding 200 ° C., such as polyimide (Tg 260 ° C.), polyamide imide (Tg 250 ° C.), polyether imide (Tg 220 ° C.), polyether sulfone (Tg 220 ° C.), a plasticizer is added. Therefore, it is considered effective to improve the yield point.

  Further, the density of the electrolyte membrane of the present invention is preferably 1.9 or less, and more preferably 1.7 or less. Generally, as the fluorine content in the electrolyte membrane material increases, the density tends to increase. Thus, in the present invention, from the relationship between Tg and the yield point, it can be said that the density is preferably a predetermined value or less and the content of fluorine in the electrolyte membrane material is preferably small. Specifically, a hydrocarbon-based electrolyte membrane material is preferably used.

  Further, the electrolyte membrane of the present invention preferably has a proton conductivity of 0.07 S / cm or more, particularly 0.1 S / cm or more when immersed in pure water at 80 ° C. This is because if the proton conductivity of the electrolyte membrane is less than the above range, proton conductivity as an electrolyte membrane used in a fuel cell is not sufficient, and good power generation characteristics may not be obtained.

B. Membrane electrode composite Next, the membrane electrode composite of the present invention will be described. The membrane electrode assembly of the present invention is characterized by using the above electrolyte membrane. By using the above electrolyte membrane for the membrane electrode assembly, the membrane electrode assembly of the present invention can be used at a high temperature without damaging the electrolyte membrane due to a dimensional change due to swelling.

  The membrane electrode assembly of the present invention has a catalyst electrode layer bonded to both sides of an electrolyte membrane. The electrolyte membrane used at this time is the same as that described in “A. Electrolyte membrane”, and thus the description thereof is omitted here. The catalyst electrode layer bonded to both sides of the electrolyte membrane is one used as a catalyst electrode layer in a normal fuel cell, and a catalyst electrode material for forming a catalyst electrode layer of a normal fuel cell, specifically Specifically, it is formed of a material comprising a solid electrolyte membrane material and carbon powder carrying platinum or a platinum alloy.

C. Fuel Cell Next, the fuel cell of the present invention will be described. The fuel cell of the present invention uses the above electrolyte membrane. By using the electrolyte membrane in the fuel cell, the fuel cell of the present invention can be used at a high temperature without damaging the electrolyte membrane due to a dimensional change due to swelling.

  A unit cell which is the minimum power generation unit of the fuel cell of the present invention has a membrane electrode assembly in which a catalyst electrode layer is bonded on both sides of the above-described electrolyte membrane, and a gas diffusion layer on both sides of the membrane electrode complex. In addition, a separator is arranged on the outer side of the fuel gas and oxidant gas supplied to the catalyst electrode layer of the membrane electrode assembly through the gas diffusion layer, and by power generation It works to transmit the obtained current to the outside.

  The electrolyte membrane constituting such a fuel cell is the same as that described in “A. Electrolyte membrane”, and thus the description thereof is omitted here. The catalyst electrode layers bonded to both sides of the electrolyte membrane are the same as those described in “B. Membrane electrode complex”, and thus the description thereof is omitted here.

  Further, as the diffusion layer and separator used in the present invention, those normally used in fuel cells can be used, and specifically, the diffusion layer is preferably formed by molding carbon fiber or the like. The separator can be a carbon type, a metal type, or the like.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Claims (4)

An electrolyte membrane used for a solid polymer electrolyte fuel cell, wherein the strain up to a yield point by a tensile test of the electrolyte membrane having a thickness of 10 to 100 μm is 15% or more,
The electrolyte membrane having a glass transition temperature of 130 ° C. or higher. The electrolyte membrane according to claim 1, wherein the density of the electrolyte membrane is 1.9 or less. A membrane electrode assembly using the electrolyte membrane according to claim 1 or 2. A fuel cell using the electrolyte membrane according to claim 1.