KR20110125759A - Membrane electrode assembly(mea) using nano carbon materials for fuel cell and method for the same - Google Patents

Abstract

PURPOSE: A membrane electrode assembly using carbon nano material is provided to alleviate material transfer resistance and have excellent durability by including a catalyst layer with carbon nano supporter comprising a carbon black. CONSTITUTION: A membrane electrode assembly using carbon nano material comprises an electrolyte membrane and electrode. The electrode comprises a catalyst layer. The catalyst layer is in the both sides of the electrolyte membrane. The catalyst layer comprises conducting material of 0.05- 0.3 parts by weight relative to a carbon nano supporter of 1 part by weight. The catalyst layer mainly consists of a metal deposition electrocatalyst including a high endurance carbon nano supporter of a two dimensional structure and additionally consists of conductive material of a three dimensional structure and an ionomer binder for forming pores. The carbon nano supporter is the one or more kind of mixture which is selected from the group of a carbon nano fiber, carbon nano tube, carbon nano wire, carbon nano ring, and carbon nano horn.

Description

Membrane electrode assembly (MEA) using nano carbon materials for fuel cell and method for the same}

The present invention relates to a catalyst layer of a membrane electrode assembly (MEA) for a polymer electrolyte fuel cell, and more particularly, to improve electrode performance including a catalyst carrier using carbon nanomaterial and carbon black and a catalyst including the same. The present invention relates to a membrane electrode assembly for a fuel cell and a method of manufacturing the same.

A fuel cell is a cell that directly converts chemical energy generated by oxidation of a fuel into electrical energy. The most typical one is a hydrogen-oxygen fuel cell.

Fuel cells are more efficient than conventional internal combustion engines, have less emissions of nitrogen oxides and sulfide oxides that cause air pollution, and can significantly reduce carbon dioxide emissions, resulting in greater environmental conservation. In addition, since hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol, and natural gas are used, various fuels can be used, and noise and vibration are virtually eliminated.

The fuel cell has a structure surrounding the electrolyte with two electrodes, and depending on the type of electrolyte, a solid polymer fuel cell (PEFC, or proton exchange), an alkaline fuel cell (PAFC), and a molten carbonate type ( Molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), and representative examples are Polymer Electrolyte Membrane Fuel Cell (PEMFC) and Direct Methanol Fuel Cell (DMFC). ).

The polymer electrolyte fuel cell (PEMFC) has a high output density and energy efficiency, operates at room temperature, and has a simple device configuration, which can be widely used as a home power generation system, a power source for mobile communication equipment, and a power source for automobiles.

In the polymer electrolyte fuel cell, a membrane electrode assembly (MEA) is located at the center, and the MEA includes an anode (also referred to as a “fuel electrode”) and a cathode (also referred to as an “air electrode” or an “oxygen electrode”) of the polymer electrolyte membrane. Located on both sides, the electrocatalyst slurry is coated on a polymer electrolyte membrane and dried to prepare a catalyst layer between the two electrodes.

The principle of the polymer electrolyte fuel cell is that the fuel is supplied to the anode, the anode, and adsorbed and oxidized in the catalyst layer to generate hydrogen ions and electrons. The generated electrons reach the cathode, which is an anode, according to an external circuit, and hydrogen ions are transferred to the cathode through the polymer electrolyte membrane. The cathode is supplied with an oxidant and generates electricity while hydrogen ions and electrons react on the catalyst of the cathode to produce water.

At this time, the catalyst layer is porosity is important because the gaseous material must be sufficiently moved to the reaction point. For this purpose, porous carriers have been mainly used. The porous carrier should reduce the pressure loss by increasing the pore fraction and increasing the pore size in order to supply the reaction gas smoothly, but as the pore fraction increases, the density of the material itself decreases and the strength thereof becomes weak.

In addition, the fuel cell carrier must have excellent electrical conductivity, and carbon-based supports such as carbon black have been used in this respect. However, in general, the carbon support damages the structure of the carbon support due to the electrochemical corrosion during the electrochemical reaction in the fuel cell, thereby reducing the electrical conductivity due to the loss of the electric conduction network and the electrocatalyst performance due to the loss of the platinum supported on the carbon support. It causes problems such as decrease.

For this purpose, platinum-supported catalysts are used on highly graphitized materials such as carbon nanotubes (CNT) or carbon nanofibers (CNF), which are highly durable carbon supports. Indeed, such electrode catalysts using CNT or CNF as a support show superior durability compared to electrode catalysts using carbon black as a support. However, in the basic performance of the membrane electrode assembly, the membrane electrode assembly using Pt / CNT or Pt / CNF as the electrode catalyst is inferior to the membrane electrode assembly using Pt / C as the electrode catalyst. Since CNTs or CNFs have a two-dimensional structure, when a large amount of electrode catalysts are formed in the form of a slurry as a coating on the surface of the electrolyte membrane, the porosity decreases, resulting in a very dense structure. Difficulties in securing performance.

Therefore, the present invention is a membrane electrode assembly for a fuel cell comprising an electrode having a catalyst layer on both sides of the electrolyte membrane, the catalyst layer using a carbon nano material to ensure the durability of the catalyst-carrying carbon nano to improve the performance of the electrode An object of the present invention is to provide a membrane electrode assembly comprising a support and a method of manufacturing the same.

In order to solve the above technical problem, the present invention is a fuel cell membrane electrode assembly comprising an electrolyte membrane and an electrode provided with a catalyst layer on both sides of the electrolyte membrane, the catalyst layer is a high-durability carbon nano support having a two-dimensional structure The metal-supported electrode catalyst is included as a main component, and a conductive material and an ionomer binder having a three-dimensional structure are added to form pores.

The conductive material having the three-dimensional structure includes carbon black, activated carbon, fullerene, graphite, and mixtures thereof, and more preferably, acetylene black is used. Acetylene black is produced by pyrolysis of acetylene and has a good electrical conductivity due to its chain structure.

The conductive material has a three-dimensional structure with a particle size of 10 ~ 300nm, the particle size of the above range is more preferable for the pore formation and durability of the electrode catalyst.

As shown in FIG. 1, since the conductive material has a three-dimensional structure, the conductive material is inserted into a high-durability carbon nano support having a two-dimensional structure, thereby securing pores of the carbon nano support on which an active metal such as platinum is supported to smoothly diffuse gas. It can be planned. The addition amount of the conductive material for optimizing the electrode performance is preferably 0.05 to 0.3 parts by weight, more preferably 0.075 to 0.15 parts by weight, based on 1 part by weight of the carbon nano support carrying the active metal such as platinum. Accordingly, due to the improved porosity of the membrane electrode assembly catalyst layer, the fuel cell according to the above range may exhibit better electrochemical performance due to smoother gas diffusion and a decrease in diffusion resistance.

The high durability carbon nano support of the two-dimensional structure is characterized in that any one or a mixture of two or more selected from the group consisting of carbon nanofibers, carbon nanotubes, carbon nanowires, carbon nano ring and carbon nanohorn.

The carbon nano support is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu , Zn, Sn, Mo, W, Rh and a transition metal selected from the group consisting of a combination thereof) and a metal catalyst selected from the group consisting of a combination of 10 to 80% by weight. Outside the above range, electrode performance may be degraded.

The present invention provides a fuel cell comprising the membrane electrode assembly for fuel cells described above.

The present invention not only manufactures fuel cell membrane electrode assemblies by mixing carbon black (CB) in an electrode catalyst such as Pt / CNT or Pt / CNF, but also carbon nanotubes (CNT) and carbon nanofibers (CNF). After mixing a carbon nanomaterial having a two-dimensional structure such as carbon and a carbon material having a three-dimensional structure such as carbon black, platinum is supported on the mixed carbon material to prepare an electrode catalyst, and to prepare a membrane electrode assembly using the electrode catalyst. Even if the same effect. In addition, even when the electrode catalyst having a two-dimensional structure such as Pt / CNT and the electrode catalyst having a three-dimensional structure such as Pt / CB can be realized the same diffusion resistance reduction effect. However, in this case, when the content of Pt / CB is too high, the durability of the electrode may be significantly reduced, so that the electrode catalyst having a three-dimensional structure does not exceed 50 wt%.

The effect of the present invention can be more remarkable in the case of a membrane electrode assembly having a very dense catalyst layer structure produced by the decal method, and this decal process consists of the following three steps.

(1) uniformly mixing the catalyst slurry composition comprising the electrode catalyst, ionomer, and solvent to prepare an electrode ink

(2) Electrode ink is coated on a transfer release film through a coating process such as doctor blade method, gravure coating method, dip coating method, silk printer method, slot die method, spray coating method, or coating method to form an electrode catalyst layer. Steps to

(3) transferring the electrode catalyst layer to a hydrogen ion conductive film through a hot pressing process at a high temperature and high pressure.

The membrane electrode assembly including a catalyst layer having a carbon nano support incorporating carbon black according to the present invention has the advantage of not only alleviating material transfer resistance in the electrode catalyst layer, but also having excellent durability. This has the effect of optimizing the performance of the fuel cell including the membrane electrode assembly.

1 illustrates a cross-sectional shape of a Pt / CNF electrode structure in which carbon black is inserted according to the present invention.
Figure 2 shows the cell voltage according to the current density of Example 1, Example 2 and Comparative Example 1.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Catalyst bed  Forming Slurry  Produce

(Example 1)

0.075 g of carbon black was added to 1 g of nanofibers (Pt / CNF) carrying platinum catalyst, and a catalyst-forming composition including Nafion suspension, 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 15-25% by weight based on total solids.

(Example 2)

0.15 g of carbon black was added to 1 g of nanofibers (Pt / CNF) carrying platinum catalyst, and a catalyst-forming composition including Nafion suspension, 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 15-25% by weight based on total solids.

(Comparative Example 1)

A catalyst composition comprising Nafion suspension, which is a hydrogen ion conductive binder resin, and an IPA aqueous solution solvent, was prepared as shown in Table 1 without putting carbon black in 1 g of nanofibers (Pt / CNF) loaded with a platinum catalyst. The Nafion ionomer content was set to 15-25% by weight based on total solids.

Table 1. Preparation of slurry for catalyst layer formation

Preparation of Membrane Electrode Assembly

The slurry for forming the catalyst layer of Examples 1, 2 and Comparative Example 1 was coated on the thin film by a doctor blade method to a predetermined thickness, and transferred to the Nafion film under 120-150 ^o C, 100-300 kgf / cm ² condition. To prepare a membrane electrode assembly (MEA). The platinum loading of the MEA thus prepared was maintained at about 0.4 mg / cm ² .

Fuel Cell Performance Evaluation

A membrane electrode assembly prepared from the slurry for forming catalyst layers of Examples 1, 2 and Comparative Example 1 has a relative humidity of 100%, a gas utilization rate of 70% / 40% using hydrogen and air as fuel, atmospheric pressure operation, and a cell temperature of 70 degrees. The performance of the MEA was evaluated in the form of unit cells under the operating conditions. As a result, MEA (Example 1 and Example 2) to which carbon black was added 0.075 g and 0.15 g based on 1 g of Pt / CNF catalyst, respectively, was added to MEA (Comparative Example 1) to which carbon black was not added. Therefore, it can be seen that the fuel cell performance is improved.

Membrane Electrode Assembly  Pore distribution measurement

In order to analyze the pore distribution of the catalyst layer of the membrane electrode assembly prepared by the composition of Example 2 and Comparative Example 1, it was measured by using a mercury permeation porosimeter (Autopore IV 9500, Micromeritics) and the results are shown in FIG. In fact, when CB was added to Pt / CNF, the pore volume in the range of 20 to 100 nm was remarkably increased. In fact, these ranges of pores are reported to play an important role in fuel cell performance, and in FIG. 3, it is determined that an increase in pore volume contributes to an improvement in fuel cell performance.

Claims (9)

In the membrane electrode assembly for a fuel cell comprising an electrolyte membrane and an electrode provided with a catalyst layer on both sides of the electrolyte membrane,
The catalyst layer is mainly composed of a metal-supported electrode catalyst including a high-durability carbon nano support having a two-dimensional structure, and a membrane electrode assembly for a fuel cell, wherein a conductive material and an ionomer binder having a three-dimensional structure are added to form pores. .
The method of claim 1,
The carbon nano support is any one or a mixture of two or more selected from the group consisting of carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanowires, carbon nanorings and carbon nanohorns. Membrane electrode assembly.
The method of claim 1,
The catalyst layer is a fuel cell membrane electrode assembly comprising 0.05 to 0.3 parts by weight of conductive material based on 1 part by weight of carbon nano support.
The method according to claim 1 and 3,
The conductive material is a fuel cell membrane electrode assembly comprising a carbon material consisting of carbon black, activated carbon, fullerene, graphite and mixtures thereof.
The method of claim 4, wherein
Membrane electrode assembly for a fuel cell, characterized in that the conductive material has a particle size of 10nm ~ 300nm.
The method of claim 4, wherein
Membrane electrode assembly for a fuel cell comprising the carbon black is acetylene black prepared for pyrolysis of acetylene.
The method of claim 1,
The metal supported electrode catalyst is a fuel cell membrane electrode assembly, characterized in that 10 to 80% by weight of the metal is supported.
The method according to claim 1 and 7,
The metal is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn And a transition metal selected from the group consisting of Sn, Mo, W, Rh, and combinations thereof, and a membrane electrode assembly for a fuel cell comprising a combination thereof.
A fuel cell comprising any one of the fuel cell membrane electrode assemblies selected from claim 1.

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