KR20140126597A - Fuel battery membrane electrode assembly comprising micro graphite and method thereof - Google Patents

Abstract

The present invention relates to a method for preparing an electrode catalyst and a membrane electrode complex for a fuel cell using micro-graphite. The method includes the steps of: carrying a metal catalyst in a carbon support to prepare a commercial catalyst; spraying catalyst slurry of an anode in which the commercial catalyst is used on one surface of an electrolyte membrane using a spray gun; spraying catalyst slurry of a cathode containing micro-graphite on the other surface of the electrolyte membrane; and mixing after ultrasonic treatment using binding. According to the present invention, the electrode catalyst and the membrane electrode complex for a fuel cell using micro-graphite has electric conductivity, thermal stability and durability and, therefore, can be effectively used as novel fuel cells.

Description

TECHNICAL FIELD [0001] The present invention relates to a membrane electrode assembly for a fuel cell containing micrographite and a method for manufacturing the same,

The present invention relates to an electrode catalyst and a membrane electrode assembly for a fuel cell using micrographite having improved electrical conductivity, thermal stability and durability, and a method for producing the same.

A fuel cell is a device that generates electrical energy by electrochemically reacting a fuel and an oxidant. This chemical reaction is carried out by the catalyst in the catalyst bed and is generally capable of continuous power generation as long as the fuel is continuously supplied. Unlike conventional power generation systems where efficiency is lost during various stages, fuel cells can produce direct electricity, which is twice as efficient as internal combustion engines and can also reduce concerns about environmental pollution and resource depletion. have.

A fuel cell is an electrochemical device that converts the chemical energy of hydrogen (H ₂ ) and oxygen (O ₂ ) contained in a hydrocarbon-based material such as methanol, ethanol and natural gas into direct electrical energy. (anode) and cathode (cathode), respectively, to continuously generate electricity.

Such a fuel cell is classified into a high temperature type fuel cell and a low temperature type fuel cell depending on the operating temperature. Of these, low-temperature fuel cells include a polymer electrolyte membrane cell (PEMFC) and a direct liquid fuel cell (DLFC). When methanol is used as the fuel in the direct liquid fuel cell, it is referred to as a direct methanol fuel cell (DMFC). The polymer electrolyte fuel cell is a fuel cell using a polymer membrane having hydrogen ion-exchange properties as an electrolyte. The fuel cell includes a solid polymer electrolyte fuel cell (SPEFC), a solid polymer fuel cell (SPFC), a polymer electrolyte fuel cell (PEFC) exchange membrane fuel cell (PEMFC). Polymer electrolyte fuel cells with lower operating temperatures than other types of fuel cells have high efficiency, high current density and power density, short startup times and fast response to load changes (LJMJ Blomen and MN Mugerwa, " Fuel Cell Systems ", Plenum Press, New York, 1993).

Especially, since the polymer membrane is used as the electrolyte, there is no electrolyte loss, and it is possible to apply the methanol reformer, which is an established technology, and is less sensitive to the change of the reaction gas pressure. In addition, the design is simple, easy to manufacture, and various materials can be used for the fuel cell body material, and the volume and weight are smaller than those of a phosphoric acid fuel cell having the same principle of operation. In addition to these characteristics, the polymer electrolyte fuel cell can be applied to a wide variety of fields such as power source for non-polluting vehicles, locally installed power generation, space power, mobile power, and military power.

Korean Patent Laid-Open No. 2010-001286259 discloses an electrode catalyst for fuel cells having excellent durability, and discloses a method for producing an electrode catalyst for a fuel cell using a catalyst containing platinum as an active ingredient.

In general, a catalyst containing platinum (Pt) as an active component is used as a constituent element of an anode and a cathode. However, since platinum-based catalysts have a small amount of reserves and are expensive, they are a large part of the total cost of producing fuel cells, which is a hindrance to the mass production and commercialization of fuel cells. Therefore, it is necessary to develop a new catalyst material having excellent efficacy while reducing the use of Pt as a fuel cell catalyst material.

Korea Patent Publication No. 2010-001286259

In order to solve the above-mentioned problems, an object of the present invention is to provide a method for manufacturing a membrane electrode assembly for a fuel cell having improved thermal stability, electrical conductivity and durability.

Another object of the present invention is to provide an electrolyte membrane; An anode electrode including a catalyst layer for an anode electrode formed between the electrolyte membrane; And a cathode electrode including a catalyst layer for a cathode electrode.

Another object of the present invention is to provide a fuel cell including a membrane electrode assembly according to the method of the present invention.

Accordingly, the present invention provides a method of manufacturing a carbon-based catalyst, comprising: preparing a catalyst having a metal catalyst supported on a carbon support; Forming a catalyst layer for an anode electrode by spraying a catalyst slurry of the anode including the catalyst on one surface of the electrolyte membrane; Forming a catalyst layer for a cathode electrode by spraying a cathode catalyst slurry obtained by adding micrographite (MG) to a catalyst having a metal catalyst supported on a carbon support, on the other surface of the electrolyte membrane; And thermocompression bonding the catalyst layer using a thermocompressor. The present invention also provides a method for manufacturing a membrane electrode assembly for a fuel cell.

In one embodiment of the present invention, the carbon support may be selected from the group consisting of carbon black, graphite carbon, carbon nanotube, acetylene black, Ketjen black, Carbon fibers, and carbon fibers.

In one embodiment of the present invention, the metal catalyst comprises at least one of platinum, ruthenium, osmium, platinum-palladium, platinum-ruthenium alloy, platinum-cobalt alloy, platinum-nickel alloy, platinum-iridium alloy and platinum- Lt; / RTI >

In one embodiment of the present invention, the cathode catalyst slurry may include a catalyst supported on a carbon support and a micrographite (MG) at a weight ratio of 3: 1 to 6: 1.

In one embodiment of the present invention, the slurry may be isopropyl alcohol and Nafion solution.

In an embodiment of the present invention, the metal loading used for forming the anode catalyst layer may be 0.4 mg / cm 2.

In an embodiment of the present invention, the metal loading used to form the cathode catalyst layer may be 0.34 mg / cm 2.

In one embodiment of the present invention, the method may further include bonding the gas diffusion layer to both sides of the thermally compressed membrane electrode assembly.

In one embodiment of the present invention, the thermocompression bonding may be performed at a temperature of 120 to 140 ° C. and a pressure of 4 to 6 MPa for 130 to 160 seconds.

The present invention also provides an electrolyte membrane comprising: an electrolyte membrane; An anode electrode including a catalyst layer for an anode electrode formed between the electrolyte membrane; There is provided a membrane electrode assembly for a fuel cell comprising a cathode electrode including a catalyst layer for a cathode electrode. In this case, the anode electrode may be formed by applying a catalyst layer for an anode according to the method of the present invention, and the cathode may be formed by applying a catalyst layer for a cathode according to the method of the present invention.

Further, the present invention provides a fuel cell including the membrane electrode assembly according to the method of the present invention.

The present invention relates to a catalyst for a fuel cell and a method for producing a membrane electrode assembly (MEA) using the micrographite (MG), and the catalyst and the membrane electrode assembly for a fuel cell using the micrographite according to the present invention have excellent electrical conductivity, Durability and thus can be usefully used as a fuel cell superior to the conventional fuel cell.

1 is a graph showing the results of X-ray diffraction analysis of vulcan and Pt / C catalyst, which are one kind of micrographite and carbon black.
2 is a graph showing a result of measuring the crystallinity of carbon through Raman analysis.
3 is a graph showing the results of electrical conductivity.
4 is a graph showing the performance evaluation of a polymer electrolyte fuel cell.
5 is a graph showing Acceleration Durability Test (ADT) results for catalyst deterioration using fuel starvation.

The present invention relates to an electrode catalyst for a fuel cell and a membrane electrode assembly using micrographite. It is based on the finding that utilizing micrographite in the production of electrode catalysts for fuel cells results in improved performance and durability.

The term " graphite " refers to a material which is easy to mechanically process, has a high thermal conductivity, has characteristics of friction, lubrication, high thermal and chemical resistance, and strength increase due to temperature rise and is hardly affected by changes in temperature or humidity There are advantages. It is also called carbon graphite.

The term " membrane electrode assembly " (MEA) refers to a hot-pressing method in which two electrodes, an anode and a cathode, are attached to a polymer electrolyte membrane.

As described above, the present invention is characterized in that a fuel cell having improved thermal stability, electrical conductivity and durability can be manufactured by using micrographite in the production of a catalyst.

The method for producing a membrane electrode assembly for a fuel cell according to the present invention comprises the steps of: preparing a catalyst carrying a metal catalyst on a carbon support; Forming a catalyst layer for an anode electrode by spraying a catalyst slurry of the anode including the catalyst on one surface of the electrolyte membrane; Forming a catalyst layer for a cathode electrode by spraying a cathode catalyst slurry obtained by adding micrographite (MG) to a catalyst having a metal catalyst supported on a carbon support, on the other surface of the electrolyte membrane; And the step of thermocompression bonding the catalyst layer using a thermocompressor.

In addition, the electrode catalyst for fuel cells using the micrographite according to the present invention uses a metal catalyst suitable for oxidation of hydrogen and reduction reaction of oxygen, and in order to increase the effective surface area of the catalyst significantly, (carbon black) on the surface of fine carbon particles such as carbon black.

The carbon support which can be used in the present invention is at least one selected from the group consisting of carbon black, graphite carbon, carbon nanotube, acetylene black, Ketjen black, (Carbon Fiber), but not limited thereto.

The metal catalyst that can be used in the present invention may be one selected from the group consisting of platinum, ruthenium, osmium, platinum-palladium, platinum-ruthenium alloys, platinum-cobalt alloys, platinum-nickel alloys, platinum-iridium alloys and platinum- May be used, and platinum may be preferably used.

In addition, the cathode catalyst slurry preferably contains a catalyst supported on a carbon support and a micrographite (MG) in a weight ratio of 3: 1 to 6: 1. According to one embodiment of the present invention, , It was confirmed that when Pt / C and MG were combined at a total weight of 5 mg, Pt / C vs. MG was used at a ratio of 4.25 mg to 0.75 mg.

According to an embodiment of the present invention, when platinum is used as the metal for forming the anode catalyst layer, the amount of loading of platinum is loaded in an amount of 0.4 mg / cm 2, Was loaded in an amount of 0.34 mg / cm < 2 >.

In addition, a step of bonding the gas diffusion layer to both sides of the thermally compressed membrane electrode assembly in the process of manufacturing the membrane electrode assembly for a fuel cell may be further performed.

The thermocompression bonding is preferably performed at a temperature of 120 to 140 ° C. and a pressure of 4 to 6 MPa for 130 to 160 seconds.

Further, the present invention provides an electrolyte membrane comprising: an electrolyte membrane; An anode electrode including a catalyst layer for an anode electrode formed between the electrolyte membrane; A membrane electrode assembly for a fuel cell including a cathode electrode including a catalyst layer for a cathode electrode, and a fuel cell including the membrane electrode assembly.

As described above, the catalyst for fuel cells using the micrographite according to the present invention and the membrane electrode assembly utilizing the same can be used as a new fuel cell in place of the membrane electrode assembly of existing fuel cells.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are only the preferred embodiments of the present invention, and the present invention is not limited by the following Examples.

< Example  1>

Electrode fabrication using micrographite

The catalyst slurry of the anode was a commercial catalyst (Johnson Matthey Inc.), and the catalyst slurry of the anode was sprayed on one side of the electrolyte membrane (NRE-212, Dupont Co.) using a spray gun. The supported amount of platinum on the anode was 0.4 mg / cm ² , and the catalyst slurry of the cathode was prepared with various contents of micrographite (MG9, HP9, JEIO Co.) (see Table 1 below). As the catalyst slurry, 500 mg of isopropyl alcohol, MG (HP9, JEIO CO.) And 1.4 mg of 5 wt% Nafion solution were used. The prepared catalyst slurry was mixed by ultrasonication and then sprayed to the cathode (0.4 mg / cm ² ) of the electrolyte membrane in an amount equal to that sprinkled on the anode. The contents of the catalyst and micrographite (MG) used in each membrane electrode assembly (MEA) are summarized in Table 1. The membrane electrode assembly had an electrode size of 5 cm ² , and a membrane electrode assembly (MEA) was placed between the polyamideimide (PAI) films and thermocompression was performed using a thermocompressor at 130 ° C., 5 MPa, and 150 seconds. Thereafter, a gas diffusion layer (GDL) was attached to both electrodes of the MEA, and they were tightened with a unit cell to produce an electrode.

Catalyst Component of Membrane Electrode Composite Electrode Anode Pt loading
(mg cm ^-2 ) Cathode Pt loading
(mg cm ^-2 ) Weight (mg) Pt / C MG Pt / C 0.4 Pt / C 0.40 5.00 - Pt / C-MG5 0.38 4.75 0.25 Pt / C-MG15 0.34 4.25 0.75 Pt / C-MG30 0.28 3.50 1.50 Pt / C-MG60 0.24 2.00 3.00

< Example  2>

Characterization of Pt / C catalyst and micrographite (MG)

The present inventors analyzed the characteristics of the micrographite (MG) and Pt / C used in the electrode preparation in Example 1. The micrographite (MG) and the amount of Pt / C were measured by using a thermogravimetric analyzer analyzer (TGA), Q50, TA Instruments) were used. The Brunauer-Emmett-Teller analyzer was used for the specific surface area measurement. The crystal structure and particle size of Pt were confirmed using an X-ray diffractometer (XRD, RAD-3C, Rigaku Corporation) at a rate of 20 min ^-1 (Cu-Kα (λ = 1.541 Å)). Raman (Thermo Fisher DXR Raman Microscope) was used to compare carbon crystallinity and surface defects of MG and Pt / C. The catalytic surface layer of carbon and Pt was characterized by SupraTM 35 scanning electron microscopy (SEM, ZEISS Co.) and energy dispersive X-ray spectroscopy (EDX).

The results of the XRD analysis of vulcan and Pt / C catalysts, which are one kind of micrographite (MG) and carbon black, are shown in FIG. 1, and the crystallinity of the carbon body between 20 and 30 degrees And the carbon crystallinity of micrographite (MG) was higher than that of vulcan and Pt / C.

FIG. 2 shows the crystallinity of carbon through the Ramam analysis. The 2D peak shows the crystallinity of carbon. The smaller the ratio (I _D / I _C ) between the G-band and the D-band, High crystallinity. Therefore, Ramam analysis showed that the micrographite had carbon crystallinity due to the presence of the 2D peak, and the I _D / I _C value of MG was also measured to be smaller than Pt / C. Therefore, it was found that the XRD analysis results and the micrographite used in the present invention have excellent carbon crystallinity.

&Lt; Example 3 >

Electrical conductivity measurement

The electric conductivity of the membrane electrode assemblies prepared in Example 1 was measured. The catalyst samples were typically Pt / C and the electrical conductivity of the other components was measured by the 4 point probe method and the electrical conductivity was measured at room temperature according to standard procedures. The sheet resistance was measured in each sample and correction factors (C.F) were applied. The sample was measured under the same conditions of the MEA, and the electric conductivity was calculated by the following equation.

V / I = ohm

ohm x CF = ohm / sq

As a result of the above equation, the resistivity can be calculated.

(ohm / sq) x Thickness (cm) = ohm.cm

Based on the above results, the resistivity of the membrane electrode assembly (MEA) can be calculated by the electrical conductivity.

As a result of the electrical conductivity analysis, as shown in FIG. 3, it was found that the higher the amount of micrographite (MG) added to Pt / C, the higher the electric conductivity. Therefore, it was found that the performance can be improved when the micrographite (MG) is applied to the fuel cell catalyst.

< Example  4>

Performance Evaluation of Polymer Electrolyte for Fuel Cell

In addition, the present inventors performed fuel cell performance evaluation on the membrane electrode composites prepared in Example 1, that is, in order to evaluate the performance of various MEAs, the temperatures of the anode, the cathode and the unit cell were set to 70 ° C The gas was injected into the unit cell at a ratio of 1.5 and 2.0, respectively, and the polarization curves of each MEA were measured to compare the performance of the unit cell.

As shown in FIG. 4, the MEAs other than Pt / C-MG60 showed higher performance than Pt / C at 0.6 V, and Pt / C-MG15 showed the highest performance. As a result, it was found that the performance was improved by increasing the electrical conductivity as MG was added. In particular, the membrane electrode composite prepared using 4.25 mg of Pt / C and 0.75 mg of MG had the best performance .

< Example  5>

Durability analysis measurement

In order to analyze the durability analysis of the membrane electrode assembly manufactured by the method of the present invention, the degradation of the catalyst was accelerated by the use of fuel starvation, and the change of the performance was examined.

As a result, as shown in FIG. 5, Pt / C decreased by 60% from the initial performance based on 0.6 V, and Pt / C-MG15 decreased by 25%. Therefore, it was found that the durability of the fuel cell was increased only by the addition of the MG, and the durability of the Pt / C-MG15 was particularly increased.

< Example  6>

Mass activity  compare

The mass activity according to the Pt content of the electrode used in the present invention was analyzed. As a result, as shown in Table 2, the mass activity was higher than Pt / C in all the electrodes to which MG was added, and the highest mass activity was observed in Pt / C-MG15 added with 15% Respectively.

Electrode TGA (Wt.%) Mass activity at 0.6 V (A mg ^-1 _Pt ) Pt / C 40.7 1.75 Pt / C-MG5 38.2 1.84 Pt / C-MG15 35.6 2.35 Pt / C-MG30 30.9 2.32 Pt / C-MG60 24.7 2.08

Therefore, the electrocatalyst for a fuel cell and the membrane electrode assembly (MEA) using the same, in which micro graphite (MG) is added to the Pt / C catalyst according to the present invention show improved electrical conductivity, thermal stability and durability, Catalyst and membrane electrode assembly. Especially, when the amount of micrographite (MG) is 15%, the effect is most excellent.

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. It is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (11)

Preparing a catalyst having a metal catalyst supported on a carbon support;
Forming a catalyst layer for an anode electrode by spraying a catalyst slurry of the anode including the catalyst on one surface of the electrolyte membrane;
Forming a catalyst layer for a cathode electrode by spraying a cathode catalyst slurry obtained by adding micrographite (MG) to a catalyst having a metal catalyst supported on a carbon support, on the other surface of the electrolyte membrane;
Wherein the catalyst layer comprises thermocompression-bonding the catalyst layer using a thermocompressor. The method according to claim 1,
The carbon support may be one selected from the group consisting of carbon black, graphite carbon, carbon nanotube, acetylene black, Ketjen black and carbon fiber. Wherein the membrane electrode assembly is at least one selected from the group consisting of a membrane electrode assembly and a membrane electrode assembly. The method according to claim 1,
Wherein the metal catalyst is at least one selected from the group consisting of platinum, ruthenium, osmium, platinum-palladium, platinum-ruthenium alloy, platinum-cobalt alloy, platinum-nickel alloy, platinum-iridium alloy and platinum- Wherein the membrane electrode assembly is formed of a membrane electrode assembly. The method according to claim 1,
Wherein the cathode catalyst slurry comprises a catalyst supported on a carbon support and a micrographite (MG) in a weight ratio of 3: 1 to 6: 1. The method according to claim 1,
Wherein the slurry is prepared by using isopropyl alcohol and a Nafion solution. The method according to claim 1,
Wherein a metal loading amount used to form the catalyst layer for an anode is 0.4 mg / cm 2. The method according to claim 1,
Wherein a loading amount of metal used for forming the cathode catalyst layer is 0.34 mg / cm &lt; 2 &gt;. The method according to claim 1,
And bonding the gas diffusion layers to both sides of the thermocompression-bonded membrane electrode assembly. The method according to claim 1,
Wherein the thermocompression bonding is performed at a temperature of 120 to 140 DEG C and a pressure of 4 to 6 MPa for 130 to 160 seconds. An electrolyte membrane; An anode electrode including a catalyst layer for an anode electrode formed between the electrolyte membrane; 1. A membrane electrode assembly for a fuel cell comprising a cathode electrode including a catalyst layer for a cathode electrode,
Wherein the anode electrode is formed by applying a catalyst layer for an anode according to the method of claim 1, and the cathode electrode is formed by applying a catalyst layer for a cathode according to the method of claim 1. 11. A fuel cell comprising the membrane electrode assembly of claim 10.

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