KR101112693B1 - Membrane-electrode assembly of fuel cell and preparing method thereof - Google Patents

Abstract

The present invention relates to a membrane electrode assembly (MEA) for a fuel cell, and a method for manufacturing the same, and more particularly, to a membrane electrode assembly for a fuel cell that exhibits excellent performance under high humidity or high current density conditions. The positive electrode catalyst layer constituting the membrane electrode assembly for fuel cell according to the present invention is characterized in that an inorganic material such as titania powder is added to enable moisture control in the electrode catalyst layer. In the fuel cell including the membrane electrode assembly according to the present invention, the excessive moisture phenomenon of the electrode catalyst layer is suppressed, so that the transfer of the reactant is performed smoothly, thereby improving performance and stability.

Fuel Cell, Membrane Electrode Assembly, Titania, Overwater

Description

Membrane-electrode assembly of fuel cell and preparing method

The present invention relates to a membrane electrode assembly (MEA) for a fuel cell and a method for manufacturing the same, and more particularly, a membrane electrode which suppresses the excessive moisture phenomenon and facilitates the transfer of the reactant through moisture control in the electrode catalyst layer. It relates to a conjugate.

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

In general, fuel cells are generally alkaline fuel cells (AFC), phosphate (Phosphoric Acid Fuel Cell (PAFC)), molten carbonate (Molten Carbonate Fuel Cell (MCFC)), solids depending on the type of electrolyte used. Solid Oxide Fuel Cell (SOFC), Direct Methanol Fuel Cell (DMFC), and Polymer Electrolyte Membrane Fuel Cell (PEMFC) are classified.

The polymer electrolyte fuel cell is a clean energy source that can replace fossil energy, and has a high power density and energy conversion efficiency, can be operated at room temperature, and can be miniaturized and sealed, thereby preventing pollution of automobiles, household power generation systems, and mobile communication equipment. It can be widely used in fields such as portable power supply and military equipment.

In such fuel cell systems, the stack that substantially generates electricity may comprise several to several unit cells consisting of a membrane-electrode assembly (MEA) and a separator (also known as a bipolar plate). It has a structure stacked in dozens. The membrane-electrode assembly includes an anode electrode (also called "hydrogen electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") with a polymer electrolyte membrane including a hydrogen ion conductive polymer therebetween. Has a bonded structure.

On the other hand, in PEMFC, a proton conductive polymer membrane is used as a hydrogen ion exchange membrane interposed between the anode electrode and the cathode electrode. The polymer used as the polymer membrane has high ion conductivity, electrochemical safety, mechanical properties as a conductive membrane, and operating temperature. The requirements must be met, such as thermal stability in sintering, manufacturability as a thin film to reduce resistance, and a low expansion effect in the presence of liquids. Currently, a perfluorosulfonic acid polymer membrane having a fluorinated alkylene in the main chain and having a sulfonic acid group at the terminal of the fluorinated vinyl ether side chain is used (for example, manufactured by Nafion, Dupont). In the case of Nafion, water is required to show ionic conductivity, so it is operated under sufficient humidification conditions while supplying water to an electrode through an external humidifier. When water is supplied excessively, a 'floating' phenomenon occurs and the reaction gas inside the electrode. Inhibits the movement of and lowers the battery performance. When the water supply is insufficient, the ionic conductivity of the Nafion electrolyte membrane decreases, thereby reducing the battery performance. Therefore, effective moisture management inside the battery is an important factor in improving battery performance.

Until now, many approaches to improving fuel cell performance by adding hydrophilic inorganic materials such as titania, silica, and alumina to MEA have been developed to solve the problem of reduced battery performance due to reduced ion conductivity in low or no humid conditions. It has been going on.

However, relatively little research has been conducted to control over-moisture under high humidity conditions. In connection with this, attempts have been made to suppress water flooding by increasing the moisture content by using a composite polymer membrane in which a hydrophilic inorganic material such as SiO ₂ is mixed with the proton conductive polymer membrane, but the inorganic substance in the composite polymer membrane It is difficult to uniformly control the degree of dispersion and the manufacturing process is complicated, and as the moisture content of the proton conductive polymer membrane increases, the volume and length expansion ratio become excessive, thereby increasing the interface resistance between the proton conductive polymer membrane and the electrode interface. There was a problem of poor durability.

Accordingly, the present inventors continued to study moisture control by adding an inorganic powder to the electrode catalyst layer, thereby completing the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide a membrane electrode assembly for a fuel cell which suppresses the phenomenon of excessive moisture in the electrode catalyst layer and facilitates the transfer of the reactant.

Another object of the present invention is to provide a method for producing the membrane electrode assembly.

In order to achieve the above object, the present invention provides a membrane electrode assembly comprising a polymer electrolyte membrane and an electrode catalyst layer positioned on both sides of the polymer electrolyte membrane, wherein the electrode catalyst layer includes an inorganic material for controlling moisture. Provided is a battery membrane electrode assembly. As the inorganic material, a hydrophilic inorganic material such as silica, alumina or titania may be used, and more preferably, titania is used. At this time, the inorganic material is characterized in that it is included in both the anode electrode and the cathode electrode. The inorganic material is preferably included 15% to 30% by weight, more preferably 23% by weight based on the total solids of the catalyst layer. The membrane electrode assembly shows particularly excellent performance under high humidity conditions or high current density conditions of 100 or more relative humidity.

In order to achieve another object of the present invention, the present invention comprises the steps of forming a catalyst layer by coating a composition for forming a catalyst layer on a release film; And placing the polymer electrolyte membrane on one surface of the release film coated with the composition for forming a catalyst layer, transferring the catalyst layer to the polymer electrolyte membrane at 120 to 150 ^° C. and 50 to 200 kgf / cm ^2. Provided is a method for preparing. The composition for forming the catalyst layer is composed of a platinum catalyst (Pt / C), titania powder, a hydrogen ion conductive binder resin and an aqueous solution of isopropyl alcohol (IPA) supported on carbon, and the hydrogen ion conductive binder resin content is 20-40 based on the total solids. Weight percent.

Carbon as one of the catalyst layer forming compositions includes carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotube, carbon nanofiber, carbon nanowire, carbon nanohorn, carbon nano ring, and mixtures thereof. It is preferably selected from the group consisting of.

The hydrogen ion conductive binder resin, which is one of the composition for forming a catalyst layer, may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluoro It is preferably selected from the group consisting of rosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate, copolymers thereof and mixtures thereof.

The release film is polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinylether copolymer, ethylene / tetrafluoroethylene, polyvinylidene fluoride, air thereof A fluorine resin film selected from the group consisting of coalescing and mixtures thereof; Or a non-fluorine-based polymer film selected from the group consisting of polyimide, polyethylene, polypropylene, polyethylene terephthalate, polyester, copolymers thereof, and mixtures thereof.

The process of coating the catalyst layer formation on the release film is screen printing method, spray coating method, coating method using a doctor blade, gravure coating method, dip coating method, silk screen method, painting method, coating method using a slot die, and It can carry out by the method chosen from the group which consists of these combinations.

 The polymer electrolyte membrane may be a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain.

The polymer resin may be a fluoro polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer , Polyether-etherkedone-based polymer, polyphenylquinoxaline-based polymer, and combinations thereof.

The membrane electrode assembly according to the present invention is prepared by physically adding and mixing inorganic materials such as titania powder to the catalyst layers of both the anode electrode and the cathode electrode, thereby providing excellent fuel cell performance and stability even under flood conditions where sufficient humidification or water is generated. It is effective for the manufacture of a fuel cell.

In the present invention, the high humidification condition means a case where the relative humidity is 100 or more, and the high current density condition means a condition where the relative humidity is less than 100 but the current density is 800 mA / cm ² or more. The present invention relates to the addition of inorganic powder, in particular titania, to the electrode catalyst layer of the MEA, characterized in that the inorganic powder is physically mixed and added to both the anode electrode and the cathode electrode. 1 shows a structural diagram of a membrane electrode assembly according to the present invention in which titania is added to an electrode catalyst layer.

The flooding of the electrode, ie, the phenomenon that the performance of the electrode is reduced by temporarily increasing the liquid water around the electrode and preventing the reaction gas of hydrogen and oxygen from penetrating into the electrode, can occur not only at the cathode but also at the anode. The purpose is to prevent flooding of the electrodes by applying them to both the anodes as long as the basic performance of the electrodes is not impaired.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples and the present invention is not limited to the following examples.

Examples 1 to 3: Preparation of the composition for catalyst formation

A catalyst-forming composition comprising a platinum catalyst (Pt / C) supported on carbon, a titania powder, a Nafion solution which is a hydrogen ion conductive binder resin, and an IPA aqueous solution solvent was prepared as shown in Table 1 below. The Nafion ionomer content was set to 30% by weight based on total solids.

Comparative example  1-2: Preparation of the composition for catalyst formation

A catalyst-forming composition comprising a platinum catalyst (Pt / C) supported on carbon, a titania powder, a Nafion solution which is a hydrogen ion conductive binder resin, and an IPA solvent was prepared as shown in Table 2 below. The Nafion ionomer content was set to 30% by weight based on total solids.

Example  4-6: Production of membrane electrode assembly

The catalyst layer-forming composition of Examples 1 to 3 was coated with the same thickness on the thin film by the doctor blade method, and the MEA was prepared by transferring the catalyst layer to the Nafion film at 140 ^° C. and 100 kgf / cm ² . The platinum loading of the MEA thus prepared was maintained at about 0.3 mg / cm ² .

Comparative Examples 3 to 4: Preparation of Membrane Electrode Assembly

The composition for forming a catalyst layer of Comparative Examples 1 and 2 was coated with the same thickness on a thin film by a doctor blade method, and a MEA was prepared by transferring the catalyst layer to a Nafion film at 140 ^° C. and 100 kgf / cm ² . The platinum loading of the MEA thus prepared was maintained at about 0.3 mg / cm ² .

Test Example 1: Performance Test of Fuel Cell

With the membrane electrode assembly of Example 5 and Comparative Example 3, the performance test was performed under different humidification conditions. The results are shown in Figures 2a to 2c.

As can be seen from the figure, the low-humidity performance was almost the same regardless of the presence or absence of titania, but the MEA added with titania under high-humidity conditions showed a relatively good performance, especially in the high current density region.

Test Example 2: Fuel Cell Performance Test

Impedance analysis was performed using the membrane electrode assembly of Example 5 and Comparative Example 3 by varying the humidification conditions and the current density. The results are shown in 3a to 3d.

As can be seen from the figure, even in impedance analysis, it can be seen that the MEA added with titania in a high humidification condition and a high current density region has a relatively low reaction resistance. In particular, when Titania is added in the diffusion resistance region, it can be seen that the value is low, which can be considered that cell flooding caused by excess water generated in the high humidity and high current density region is alleviated by Titania.

Test Example 3: Fuel Cell Performance Test

With the membrane electrode assembly of Example 5, the performance test was carried out at different current densities. Sufficiently humidified gas of RH 100 or higher was used as fuel. The results are shown in FIG.

As can be seen from the figure, it can be seen that the performance of the MEA is improved, especially in the high current density region, when the titania is added. The titania content shows the highest performance at around 23% and there is no synergistic effect at higher titania content. The synergistic effect of MEA performance due to the addition of titania is that the excess moisture generated in the MEA catalyst layer during the electrochemical reaction due to the addition of titania powder is absorbed into the titania micropores to prevent flooding in the Pt / C catalyst layer. I think it is.

Test Example 4: Fuel Cell Performance Test

With the membrane electrode assembly of Examples 4-6 and Comparative Examples 3-4, the performance test was carried out under high humidity conditions of relative humidity 110. The results are shown in FIG.

As can be seen from the figure, when a small amount of titania is added under high humidity conditions of a relative humidity of 110, there is no particular change in performance, but a significant increase in performance is observed at 23% by weight, and at higher contents, the performance tends to decrease again. can confirm. In addition, when the titania content is 17%, 23% and 29%, it can be seen that the results are excellent in high humidification compared to MEA without adding titania.

1 is a structural diagram of a membrane electrode assembly (MEA) according to the present invention in which titania is added to an electrode catalyst layer,

2A to 2C are graphs of performance test results of the membrane electrode assembly (MEA) under different humidification conditions.

3A to 3D are graphs of impedance analysis test results of a membrane electrode assembly (MEA) at different humidification conditions and current densities.

4 is a graph showing the results of performance tests performed with different current densities with the membrane electrode assembly of Example 5;

5 is a graph of a performance test result in a high humidification condition of relative humidity 110.

Claims (13)

A membrane electrode assembly comprising a polymer electrolyte membrane and an electrode catalyst layer positioned on both sides of the polymer electrolyte membrane, wherein the inorganic catalyst for controlling moisture under high humidification conditions is 15% to 30% by weight based on the total solids of the catalyst layer. Membrane electrode assembly for fuel cell, characterized in that it is included. The method of claim 1, The inorganic material is a membrane electrode assembly for a fuel cell, characterized in that the titania powder. The method of claim 1, The inorganic material is a membrane electrode assembly for a fuel cell, characterized in that included in both the anode electrode and the cathode electrode. delete delete (a) coating the catalyst layer forming composition on a release film to form a catalyst layer; And (b) transferring the catalyst layer to the polymer electrolyte membrane at 120 to 150 ° C. and 50 to 200 kgf / cm 2 after placing the polymer electrolyte membrane on one surface of the release film coated with a composition for forming a catalyst layer, Wherein the composition for forming a catalyst layer is a method for producing a membrane electrode assembly for a fuel cell such that an inorganic material for controlling moisture under high humidification conditions is included in an amount of 15 wt% to 30 wt% based on the total solids of the composition for forming a catalyst layer. The method of claim 6, The release film is polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinylether copolymer, ethylene / tetrafluoroethylene, polyvinylidene fluoride, air thereof A fluorine resin film selected from the group consisting of coalescing and mixtures thereof; Or a non-fluorine-based polymer film selected from the group consisting of polyimide, polyethylene, polypropylene, polyethylene terephthalate, polyester, copolymers thereof, and mixtures thereof. The method of claim 6, The composition for forming the catalyst layer is composed of a platinum catalyst (Pt / C), titania powder, a hydrogen ion conductive binder resin and an aqueous solution of isopropyl alcohol (IPA) supported on carbon, and the hydrogen ion conductive binder resin content is 20 to 40 based on the total solids. A method for producing a fuel cell membrane electrode assembly, characterized in that the weight%. The method of claim 6, The process of coating the catalyst layer formation on the release film includes screen printing, spray coating, doctor blade coating, gravure coating, dip coating, silk screening, painting, slot die coating, and these Method of manufacturing a membrane electrode assembly for a fuel cell that is carried out by a method selected from the group consisting of a combination of two. The method of claim 6, The polymer electrolyte membrane is a method for producing a membrane electrode assembly for a fuel cell is a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. 11. The method of claim 10, The polymer resin may be a fluoropolymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, A method for producing a membrane electrode assembly for a fuel cell, which is selected from the group consisting of a polyether-etherkedon-based polymer, a polyphenylquinoxaline-based polymer, and a combination thereof. The method of claim 8, The hydrogen ion conductive binder resin, which is one of the composition for forming the catalyst layer, is polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, and polyperfluorosulfone. A method for producing a membrane electrode assembly for a fuel cell, which is selected from the group consisting of polyvinyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate, copolymers thereof and mixtures thereof. The method of claim 8, Carbon, which is one of the catalyst layer forming compositions, is carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotube, carbon nanofiber, carbon nanowire, carbon nanohorn, carbon nano ring, and mixtures thereof. Method for producing a membrane electrode assembly for a fuel cell selected from the group consisting of.

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