KR20110007350A - Polymer electrolyte membrane for fuel cell and low-humidified mea - Google Patents

Abstract

PURPOSE: A polymer electrolyte membrane for a fuel cell is provided to reduce the content of expensive hydrogen-ion-conductive polymers and to obtain a membrane electrode assembly with excellent electric conductivity. CONSTITUTION: A polymer electrolyte membrane(20) for a fuel cell includes a hydrogen-ion-conductive polymer(21) containing porous silica particles(22). The average particle diameter of pores of the porous silica particle is 1~10 nm. The hydrogen-ion-conductive polymer is a perfluorosulfonic acid polymer. The porous silica particles is included in the amount of 1~50 parts by weight based on 100 parts by weight of the hydrogen-ion-conductive polymer. The film for fuel cell electrode assembly(10) comprises porous electrode catalyst layers(30).

Description

Polymer electrolyte membrane for fuel cell and low-humidity membrane electrode assembly comprising same {Polymer electrolyte membrane for fuel cell and low-humidified MEA}

The present invention relates to a polymer electrolyte membrane for a fuel cell and a low-humidity membrane electrode assembly including the same, and more particularly, to a fuel cell polymer electrolyte membrane capable of reducing the content of an expensive hydrogen ion conductive polymer while maintaining the moisture content of the electrolyte membrane; It relates to a low-humidity membrane electrode assembly including the same.

Fuel cells are one of the alternative energy sources of the future, and are a type of power generation device that directly converts chemical energy in fuel into electrical energy. The fuel cells may be manufactured according to operating temperatures and types of electrolytes, such as Proton Exchange Membrane Fuel Cells;

PEMFC), Alkali Fuel Cells (AFC), Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), Solid Oxide Fuel Cells; SOFC) and the like.

Among them, the polymer electrolyte fuel cell has a lower driving temperature, higher energy conversion efficiency, higher current density and higher output density, and faster response to load changes than other fuel cells. In particular, since the polymer membrane is used as the electrolyte, the structure is simple and corrosion does not have to be considered. Therefore, there are various possibilities of material selection, and thus it can be applied to a wide variety of industrial fields such as a power source of a pollution-free vehicle, a home power source, a portable power source, and a military power source.

Such polymer electrolyte fuel cells typically use a Nafion® membrane manufactured by DU Du pont de Nemours, Inc., a tetrafluoroethylene-based copolymer containing perfluorosulfonic acid, as an electrolyte. The price of electrolytes too

Due to the high price, the cost of the membrane is required to commercialize the polymer electrolyte fuel cell. In addition, the fuel utilization rate and drastic deterioration of the driving performance due to the permeation characteristics of fuel gas and liquid (methanol) of Nafion itself improve the performance of the fuel cell by reducing the thickness of the membrane and increasing the conductivity. Attempts to reduce the use of Pion are not practical, on the contrary, increasing the thickness of the Nafion membrane lowers the conductivity and lowers the output characteristics of the fuel cell.

In addition, the Nafion polymer electrolyte has a poor numerical stability depending on the degree of hydration, which is disadvantageous in the manufacturing process, and also has a problem in that performance is degraded due to deterioration of interfacial contact with the electrode catalyst layer which is numerically stable during long time operation.

In order to solve the above problems, U.S. Patent No. 5,547,551 (WLGore & Associates, Inc.) enhances mechanical properties and numerical stability by impregnating a liquid ion conductive polymer in a porous polymer film such as stretched polytetrafluoroethylene. A method for producing a composite membrane is proposed. The composite film prepared by this method has a slightly lower proton conductivity than the Nafion film, but can produce a thin film having a thickness of about 25 μm, and thus the conductivity may be improved than that of the conventional Nafion film. In addition, US Patent No. 6,130,175 (Gore Enterprise Holdings, Inc.) was able to increase ion selectivity and improve mechanical properties by filling different ion conductive polymers on both sides of a porous polymer film such as elongated polytetrafluoroethylene. . In addition, European Patent No. 0,094,679 (Asahi Glass Co. Ltd.) also discloses a method for preparing a reinforced composite membrane by mixing and stretching a fluorine-based ion conductive polymer and polytetrafluoroethylene microfibers.

However, the porous polymer membrane replacing the Nafion membrane as described above has a problem that the most basic properties of the electrolyte membrane, such as membrane conductivity, elongation at break, low-humidity properties, etc. are inferior to the Nafion membrane.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the first problem to be solved by the present invention is to provide a polymer electrolyte membrane for a fuel cell in which cell performance is not deteriorated even under low humidity conditions.

A second object of the present invention is to provide a fuel cell membrane electrode assembly that can suppress a decrease in electrical conductivity.

The present invention to achieve the first object,

A polymer electrolyte membrane for a fuel cell including a hydrogen ion conductive polymer containing porous silica particles is provided.

According to a preferred embodiment of the present invention, the average particle diameter of the pores of the porous silica particles may be 1 ~ 10nm and the average particle diameter of the porous silica particles may be 50 ~ 1000nm.

According to another preferred embodiment of the present invention, the hydrogen ion conductive polymer may be a perfluorosulfonic acid polymer.

According to another preferred embodiment of the present invention, the porous silica particles may include 1 to 50 parts by weight based on 100 parts by weight of the hydrogen ion conductive polymer.

According to another preferred embodiment of the present invention, the thickness of the electrolyte membrane may be 20 ~ 300㎛.

The present invention to achieve the second object,

In the membrane electrode assembly for fuel cell having an electrode including a porous electrode catalyst layer on both surfaces of the polymer electrolyte membrane, the polymer electrolyte membrane uses the polymer electrolyte membrane of the present invention described above.

According to a preferred embodiment of the present invention, the electrode catalyst layer may contain graphene (graphene) loaded with a metal catalyst for a fuel cell.

According to another preferred embodiment of the present invention, the fuel cell metal catalyst may be coated with a catalyst metal particle in the core-shell type on the surface of the nano cube.

According to another preferred embodiment of the present invention, the nanocube may be oxide particles.

According to another preferred embodiment of the present invention, the oxide particles may be magnesium oxide or cupric oxide.

According to another preferred embodiment of the present invention, the catalytic metal particles may be platinum (Pt) or palladium (Pd).

According to another preferred embodiment of the present invention, the thickness of the catalyst metal particle layer coated on the nanocube particles may be 1 ~ 100nm.

According to another preferred embodiment of the present invention, the fuel cell metal catalyst may be the nanocube is magnesium oxide and the metal catalyst particles are platinum, or the nanocube is cupric oxide and the metal catalyst particles may be palladium.

Since the polymer electrolyte membrane for a fuel cell of the present invention includes a hydrophilic porous silica material therein, the moisture content of the electrolyte membrane may be kept constant. In addition, the membrane electrode assembly of the present invention not only has excellent electrical conductivity but also minimizes the content of expensive catalytic metal particles (particularly platinum) since the catalyst metal particles are coated in the core-shell type on the surface of the nano cube. Use catalyst.

In addition, when the catalyst fast particles are supported on graphene, the catalyst particles are significantly cheaper than the conventional carbon nanotubes, and have similar effects.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

As described above, the porous polymer membrane replacing the conventional Nafion membrane has a problem that membrane conductivity, breaking elongation, low-humidity properties, etc., which are the most basic physical properties of the electrolyte membrane, are inferior to those of the Nafion membrane. In addition, the Nafion membrane had a problem of inferior low-cost wettability and electrical conductivity.

Accordingly, the present invention provides a polymer electrolyte membrane for a fuel cell including a hydrogen ion conductive polymer containing porous silica particles, and a membrane electrode assembly including the same.

Specifically, when the fuel cell membrane electrode assembly according to an embodiment of the present invention is described with reference to FIG. 1, FIG. 1 is a cross-sectional view of the membrane electrode assembly for a fuel cell of the present invention. Electrode catalyst layer 30 is formed on both sides of the 20).

First, the polymer electrolyte membrane 20 will be described.

In the polymer electrolyte membrane 20 of the present invention, porous silica particles 22 are dispersed and arranged in the hydrogen ion conductive polymer 21 which is a main component of the membrane. First, as the main component of the polymer electrolyte membrane, the hydrogen ion conductive polymer 21 is not limited as long as it is a conventional hydrogen ion conductive polymer for fuel cells. Preferably, the hydrogen ion conductive polymer represented by the following Chemical Formula 1 may be used, and more preferably. Perfluorosulfonic acid polymer.

[Formula 1]

Wherein X is SO ₂ F, SO ₂ Cl, SO ₂ Br, COOR, R is (CH ₂ ) qCH ₃ , q is 0-10, m is 3-15, n is 0-1, p is 0 The integer to include. Representative examples of the hydrogen ion conductive polymer represented by Chemical Formula 1 may include Nafion Resin, manufactured by Dupont de Nemours.

As the porous silica particles 22 dispersed in the hydrogen ion conductive polymer 21 can be seen through the electron micrograph of FIG. 2, a plurality of pores are formed inside the particles to maintain a constant water content of the electrolyte membrane. Can be. In this case, the average particle diameter of the pores of the porous silica particles 22 may be 1 to 10 nm, and the average particle diameter of the porous silica particles may be 50 to 1000 nm. On the other hand, the polymer electrolyte membrane 20 may be prepared through a conventional method for producing a polymer electrolyte membrane for fuel cells, in this case preferably 1 to 50 parts by weight of porous silica particles based on 100 parts by weight of the hydrogen ion conductive polymer. can do. In addition, the thickness of the electrolyte membrane may be 20 ~ 300㎛.

Next, the electrode catalyst layer 30 formed on both surfaces of the polymer electrolyte membrane 20 will be described. In the electrode catalyst layer 30, graphene 32 is dispersed in the conductive agent 31. Specifically, the porous carbon is frequently used as an adsorbent or a catalyst carrier because it has a high specific surface area and pore volume and is stable in an acid or a base. In particular, with the development of low temperature fuel cell technology, much attention has been focused on carbon used as a carrier for fuel cell catalysts. As a metal catalyst carrier for fuel cells, carbon must have a high specific surface area to support many metals, and large pores to facilitate the formation of three-phase interface of catalyst-reactant-electrolyte, as well as high conductivity and electrochemistry to facilitate electron transfer. It must be able to withstand oxidation. In order to satisfy these requirements, the present invention utilizes a thin film-like graphene (planar plate structure) in which carbon atoms are connected in a honeycomb shape as a carrier. This can improve the stability in the electrical conductivity and oxidation conditions of the catalyst.

 The graphene 32 includes a metal catalyst 33 therein. 3A and 3B are cross-sectional views and perspective views, respectively, of the fuel cell metal catalyst of the present invention, wherein the fuel cell metal catalyst 100 is coated on the surface of the nanocube 110 and the nanocube 110 having a hexahedron shape therein. It is made of a catalytic metal particle (120). Among them, the nanocube 110 may be preferably oxide particles, and more preferably, the oxide particles may be magnesium oxide or cupric oxide. In this case, the shape of the nanocube 110 usable in the present invention is preferably in the shape of a cube, the length of one side of the cube is preferably approximately 1 ~ 1000nm. On the other hand, if the nanocube 110 has a hexahedron shape, the specific surface area becomes wider, thereby increasing reactivity.

The catalytic metal particles 120 coated on the surface of the nanocube 110 may be platinum (Pt) or palladium (Pd). In particular, in the case of using palladium as the catalyst metal particles 120, it is very advantageous in commercialization because it has a similar effect to platinum and is significantly cheaper in terms of cost. In this case, the thickness of the catalyst metal particle layer coated on the nanocube particles may be 1 to 100 nm. If the thickness of the metal particles is 1 nm or less, a problem that may be difficult to act as a catalyst may occur. There is too much usage.

On the other hand, according to a preferred embodiment of the present invention, the fuel cell metal catalyst may be the nanocube is magnesium oxide and the metal catalyst particles are platinum, or the nanocube is cupric oxide and the metal catalyst particles may be palladium.

The method for producing a metal catalyst for a fuel cell according to the present invention can be broadly classified into two types. First, after preparing magnesium oxide or cupric oxide in the nanocube form, the platinum solution is impregnated with the prepared nanocube and dried in an atmospheric atmosphere to coat platinum on the nanocube. Thereafter, the platinum-coated catalyst is reduced by using a hydrogen / nitrogen mixed gas as a carrier gas to prepare a metal catalyst for a fuel cell of the present invention.

More specifically, the method of impregnating the prepared nanocube in the platinum solution is not limited to the impregnation method, it is also possible to colloid method, precipitation method. The platinum solution is a solution in which a platinum or platinum alloy precursor is dissolved. Examples of the platinum alloy precursor include platinum chloride (H ₂ PtCl ₆ ), platinum chloride (PtCl ₂ ), and platinum oxide (Pt (NO ₃ ) ₂ ). As the solvent, distilled water, methanol or ethanol can be used. The platinum or platinum alloy precursor is dissolved in a solvent and impregnated in a nanocube of a desired type by impregnation, followed by drying for 12 to 24 hours while maintaining a temperature of 100 to 150 ° C. in an air atmosphere. The solvent is characterized in that at least one selected from the group consisting of distilled water, methanol, ethanol. As the element used in the platinum alloy, Cr, Ni, Mo, Co, Ti, Mn, Fe, Cu, Pd, Os, Ga, Zr, Hf, Ir, or a mixture thereof may be used.

Thereafter, the catalyst on which the platinum or platinum alloy precursor is supported is finally coated by a reduction reaction to coat the surface of the nanocube and dried to prepare a final catalyst.

Secondly, it is possible to fabricate a core / shell structure in which platinum is exposed through epitaxial growth on the surface of the nanocube, and detailed conditions and manufacturing methods thereof (J. Appl. Phys., 2005, 97, 10H303, (JACS, 2007, 129, 6974-6975).

As a result, in the electrode catalyst layer of the present invention, graphene was used as a carrier in place of conventional Nafion or carbon nanotubes. In this case, it can be supported by the same method as the method of supporting a catalyst in a conventional Nafion or carbon nanotubes, and preferably the catalyst of the present invention is put in a reactor, and the hydrogen / nitrogen mixed gas having a volume ratio of 1: 4 Reducing the reaction for 1 to 3 hours at a temperature of 250 ~ 350 ℃ while flowing. After the reduction reaction is cooled to room temperature in a nitrogen atmosphere to prepare a graphene (graphene) loaded with the catalyst for a fuel cell of the present invention. In this case, 0.1 to 80 parts by weight of the catalyst of the present invention may be mixed with respect to 100 parts by weight of graphene.

Thereafter, the polymer electrolyte membrane may be directly coated on the electrolyte membrane by a spray method. The direct coating method increases the utilization of the catalyst, decreases the interfacial resistance as well as increases the ionic conductivity as compared with the conventional supporting method.

As a result, the polymer electrolyte membrane for a fuel cell of the present invention includes a hydrophilic porous silica material therein, so that the moisture content of the electrolyte membrane can be kept constant. In addition, the membrane electrode assembly of the present invention not only has excellent electrical conductivity but also minimizes the content of expensive catalytic metal particles (particularly platinum) since the catalyst metal particles are coated in the core-shell type on the surface of the nano cube. Use catalyst.

In addition, when the catalyst fast particles are supported on graphene, the catalyst particles are significantly cheaper than the conventional carbon nanotubes, and have similar effects.

The present invention is a very useful invention for the chemical industry because the electrolyte membrane does not degrade the cell performance even under low-humidity conditions.

1 is a cross-sectional view of a membrane electrode assembly for a fuel cell according to a preferred embodiment of the present invention.

Figure 2 is a transmission electron micrograph of the porous silica particles contained in the polymer electrolyte membrane according to an embodiment of the present invention.

3A and 3B are cross-sectional views and schematic views of an electrode catalyst for a fuel cell according to an exemplary embodiment of the present invention.

4 is an atomic bond structure of graphene used in the present invention.

<Description of the symbols for the main parts of the drawings>

10 membrane electrode assembly 20 electrolyte membrane

22 porous silica particles 30 electrode catalyst layer

32: graphene 33: catalytic metal particles

Claims (14)

A polymer electrolyte membrane for a fuel cell comprising a hydrogen ion conductive polymer containing porous silica particles. The method of claim 1, A polymer electrolyte membrane for a fuel cell, characterized in that the average particle diameter of the pores of the porous silica particles is 1 ~ 10nm and the average particle diameter of the porous silica particles is 50 ~ 1000nm. The method of claim 1, The hydrogen ion conductive polymer is a polymer electrolyte membrane for a fuel cell, characterized in that the perfluorosulfonic acid polymer. The method of claim 1, A polymer electrolyte membrane for a fuel cell, comprising 1 to 50 parts by weight of porous silica particles based on 100 parts by weight of the hydrogen ion conductive polymer. The method of claim 1, A polymer electrolyte membrane for a fuel cell, characterized in that the thickness of the electrolyte membrane is 20 ~ 300㎛. In the membrane electrode assembly for a fuel cell having an electrode including a porous electrode catalyst layer on both surfaces of the polymer electrolyte membrane, The polymer electrolyte membrane is a fuel cell membrane electrode assembly, characterized in that the polymer electrolyte membrane of any one of claims 1 to 5. The method of claim 6, The electrode catalyst layer is a fuel cell membrane electrode assembly, characterized in that it contains graphene (graphene) loaded with a metal catalyst for the fuel cell. The method of claim 7, wherein The fuel cell metal catalyst is a fuel cell membrane electrode assembly, characterized in that the catalyst metal particles are coated in the core-shell type on the surface of the nano cube (nano cube). The method of claim 8, The nanocube is a membrane electrode assembly for a fuel cell, characterized in that the oxide particles. 10. The method of claim 9, The oxide particle is a fuel cell membrane electrode assembly, characterized in that the magnesium oxide or cupric oxide. The method of claim 8, The catalyst metal particles are platinum (Pt) or palladium (Pd) membrane electrode assembly for a fuel cell, characterized in that. The method of claim 8, Membrane electrode assembly for a fuel cell, characterized in that the thickness of the catalyst metal particle layer coated on the nanocube particles. The method of claim 8, The fuel cell metal catalyst assembly of claim 1, wherein the nanocube is magnesium oxide, the metal catalyst particles are platinum, the nanocube is cupric oxide, and the metal catalyst particles are palladium. A fuel cell comprising the membrane electrode assembly of any one of claims 7 to 13.

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