KR20110002127A - Membrane electrode assembly for direct methanol fuel cell and stack comprising the same - Google Patents

Abstract

PURPOSE: A membrane electrode assembly for direct methanol fuel cell is provided to improve material transfer by adding vapor grown carbon fibers to a catalyst layer of a fuel anode. CONSTITUTION: A membrane electrode assembly for direct methanol fuel cell comprises an anode electrode and a cathode electrode which are faced with each other, and a polymeric electrolyte membrane(300) positioned between the anode and the cathode. The anode and the cathode include electrode substrates(120,220) and catalyst layers(110,210). The catalyst layer of the anode comprises a catalyst, gas-phase grown carbon fibers and binder resin.

Description

Membrane Electrode Assembly For Direct Methanol Fuel Cell And Stack Comprising The Same}

The present invention relates to a membrane-electrode assembly of a direct methanol fuel cell and a stack including the same, and more particularly, to improve cell performance by improving mass transfer and reducing the size of catalyst particle aggregates, thereby increasing the utilization efficiency of the catalyst. And a stack comprising the membrane-electrode assembly of a direct methanol fuel cell.

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

This fuel cell is a clean energy source that can replace fossil energy, and has a merit that can produce a wide range of outputs by stacking unit cells, and has an energy density of 4 to 10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

In contrast, the direct methanol fuel cell is operated by using liquid methanol directly as a fuel, and is a new energy conversion technology that is attracting attention as a next generation mobile power source because fuel storage, system operation and maintenance are relatively simple and easy. However, in order to commercialize a direct methanol fuel cell, problems such as deterioration of the cell performance due to methanol permeation into the polymer electrolyte membrane and slow oxidation of methanol at the anode must be solved.

As such, the research on the electrode layer in a direct methanol fuel cell has been mainly focused on improving and developing a catalyst for improving the methanol oxidation reaction. However, it is equally important to optimize the electrode layer structure to increase the utilization of the catalyst and to improve mass transfer in the electrode layer.

In this regard, researches on optimizing the dispersion method such as optimizing the catalyst layer content of the Nafion ionomer, introducing a new electrode structure to improve the interfacial characteristics between the electrode and the electrolyte, or diversifying the dispersant have been preceded. Pore formation of the catalyst layer is also a major issue in this regard, studies have been made to form pores in the catalyst layer by using PTFE (poly-tetrafluoroethylene) or pore-forming additives to improve the catalyst utilization efficiency and the transferability of the catalyst layer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a membrane-electrode assembly of a direct methanol fuel cell capable of improving the performance of a unit cell by improving mass transferability, catalyst utilization efficiency, and conductivity through improving an electrode structure of an anode.

The present invention also aims to provide a stack of direct methanol fuel cells comprising the membrane-electrode assembly.

It is also an object of the present invention to provide a method for forming an anode catalyst layer of a direct methanol fuel cell which can improve the performance of a unit cell by improving mass transfer, catalyst utilization efficiency and conductivity through electrode structure improvement.

In order to achieve the above object, the present invention includes an anode electrode and a cathode electrode positioned opposite to each other and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, the anode electrode and the cathode electrode is an electrode substrate and the electrode And a catalyst layer positioned on the substrate, wherein the anode electrode catalyst layer comprises a catalyst, vapor-grown carbon fiber, and a binder resin.

The anode catalyst layer preferably comprises 2 to 4% by weight of the gas phase growth carbon fiber relative to the catalyst weight.

The catalyst layer of the anode electrode may further include carbon nanoparticles such as carbon black to further control the formation of pores by the vapor-grown carbon fiber and reinforce the function. In addition, the catalyst layer of the anode electrode provides a mass transfer path by hydrophilicity and hydrophobicity control in addition to Nafion added to the ion conductive binder resin, and in order to improve the structural durability of the electrode, PTFE (polytetrafuluoroethylene), PVDF (polyvinylidene fluoride), SBR ( styrene butadiend rubber) may be further included.

The vapor-grown carbon fiber has a diameter in the range of 100 to 300 nm, aspect ratio (fiber length / diameter ratio) is 10 or more, electrical conductivity is 100 S / cm or more, the true density is preferably 1.8 g / ml or more.

The anode electrode 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, And a catalyst selected from the group consisting of Zn, Sn, Mo, W, Rh, and combinations thereof) and combinations thereof. A platinum-ruthenium alloy catalyst may be most preferably used to prevent the catalyst poisoning phenomenon caused by CO generated during the anode electrode reaction.

The cathode electrode 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, And a catalyst selected from the group consisting of Zn, Sn, Mo, W, Rh, and combinations thereof) and combinations thereof.

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

The polymer resin may be a fluorine 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, a poly It is preferably selected from the group consisting of ether ether ketone polymers, polyphenylquinoxaline polymers and copolymers thereof.

The invention also provides a stack of direct methanol fuel cells comprising the membrane-electrode assembly according to the invention.

The present invention also comprises the step of dispersing by using ultrasonic decomposition after adding the vapor-grown carbon fiber to the excess dispersion solvent; Preparing a catalyst slurry by mixing the prepared vapor-grown carbon fiber dispersion with a catalyst and a binder resin; And applying the catalyst slurry to an electrode substrate to provide an anode catalyst layer forming method of a direct methanol fuel cell.

The dispersion solvent is preferably selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol and mixtures thereof.

The gas phase growth carbon fiber is preferably added 2 to 4% by weight based on the weight of the catalyst.

The binder resin preferably contains Nafion, which is an ion conductive binder resin.

In preparing the catalyst slurry, a binder resin selected from the group consisting of carbon black, polytetrafuluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and styrene butadiend rubber (SBR) is further added.

The vapor-grown carbon fiber has a diameter in the range of 100 to 300 nm, aspect ratio (fiber length / diameter ratio) is 10 or more, electrical conductivity is 100 S / cm or more, the true density is preferably 1.8 g / ml or more.

According to the membrane-electrode assembly for direct methanol fuel cell according to the present invention, by adding vapor-grown carbon fiber, which is a kind of carbon nanofibers, to the catalyst layer of the anode, the electrode structure is improved to induce the formation of space in the catalyst layer, thereby improving mass transfer properties. In addition, the utilization efficiency of the catalyst can be improved by reducing the size of the catalyst particle aggregate forming the catalyst layer and increasing the specific surface area.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the embodiments according to the present invention, detailed descriptions of related well-known configurations or functions will be omitted. In addition, in adding the reference numerals to the components of each drawing, the same reference numerals are added to the same components as much as possible.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and should be construed in accordance with the technical meanings and concepts of the present invention.

The embodiments described in the specification and the configuration shown in the drawings are preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, various equivalents and modifications that can replace them at the time of the present application are There may be.

1 is a view schematically showing a membrane-electrode assembly of a direct methanol fuel cell according to an embodiment of the present invention.

Referring to FIG. 1, a membrane-electrode assembly according to an embodiment of the present invention may be disposed between an anode electrode 100 and a cathode electrode 200 and the anode electrode 100 and the cathode electrode 200 positioned to face each other. It includes a polymer electrolyte membrane located.

In addition, the anode electrode 100 and the cathode electrode 200 include electrode substrates 120 and 220 and catalyst layers 110 and 210 positioned on the electrode substrates 120 and 220.

The catalyst layer 110 of the anode electrode 100 includes a catalyst, gaseous growth carbon fibers and a binder resin.

The catalyst serves to promote the oxidation reaction of methanol fuel, platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Transition metals selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh and combinations thereof) and a catalyst selected from the group consisting of combinations thereof. Specific examples include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, Pt / Ru / Sn / W and combinations thereof may be used. In a direct methanol fuel cell, a platinum-ruthenium alloy catalyst is most preferred as the anode electrode 100 catalyst in order to prevent the catalyst poisoning caused by CO generated during the anode electrode 100 reaction.

Such a platinum-based catalyst may be used as a metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbonaceous materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotube, carbon nanofiber, carbon nanowire, carbon nanoball, or activated carbon may be used, or alumina, silica, titania Inorganic fine particles such as zirconia and the like may be used, but carbon-based materials are generally used.

The binder resin is added to improve adhesion of the catalyst layer 110 and transfer hydrogen ions, and a polymer resin having hydrogen ion conductivity is used. As the hydrogen ion conductive polymer resin, a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain can be used.

Preferably, a fluorine 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, a polyether One or more hydrogen ion conductive polymers selected from ether ketone polymers or polyphenylquinoxaline polymers may be used, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), or sulfonic acid groups Copolymer of tetrafluoroethylene and fluorovinyl ether, defluorinated sulfide polyether ketone, aryl ketone, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole (poly ( 2,2 '-(m-phenylene) -5,5'-bibenzimidazole), a poly (2,5-benzimidazole), and a hydrogen ion conductive polymer selected from the group consisting of these may be used.

The binder resin may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive compound for the purpose of further improving adhesion to the polymer electrolyte membrane 300. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

Examples of the non-conductive compound include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), and ethylene / tetrafluoro Ethylene / tetrafluoroethylene (ETFE), ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dode More preferably, it is selected from the group consisting of silbenzenesulfonic acid, sorbitol, and combinations thereof.

The vapor-grown carbon fiber is a kind of nanofibers grown by decomposing hydrocarbon-based materials such as benzene or methane in the presence of a transition metal catalyst at a high temperature of 1000-1300 ℃, and has excellent mechanical strength, electrical conductivity and thermal conductivity. great. Figure 2 is a micrograph of VGCF ^®- H, Vapor-grown carbon fiber (VGCF) from Showa Denko.

The present invention improves the electrode structure by adding a vapor-grown carbon fiber to the catalyst layer 110 of the anode electrode 100 to induce the formation of space in the catalyst layer to improve the mass transfer properties, and together with the catalyst forming the catalyst layer 110 By increasing the specific surface area by reducing the size of the particle aggregates, the utilization efficiency of the catalyst is improved.

The content of the gaseous growth carbon fiber in the catalyst layer 110 is not particularly limited, but preferably 2 to 4 wt% based on the weight of the catalyst. If the content of the gas phase growth carbon fiber exceeds 4% by weight is not preferable because the catalyst layer is thickened to increase the resistance, if less than 2% by weight is not preferable because it is a slight amount to see the effect of improving the structure of the catalyst layer.

The catalyst layer 110 of the anode electrode 100 may be prepared by preparing a slurry including a gas phase growth carbon fiber, a catalyst, and a binder resin, and then applying the same to the electrode substrate 120, wherein the gas phase growth carbon fiber is well dispersed. In order to achieve this, after adding the vapor-grown carbon fiber to the dispersion solvent and dispersing the mixture using ultrasonic decomposition, the prepared dispersion is mixed with a catalyst and a binder resin to prepare a slurry, which is then used as an electrode substrate 120. It is preferable to apply | coat to and manufacture. The dispersion solvent may be preferably selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol and a mixture thereof.

The electrode substrate 120 plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer 110, thereby serving to easily access the fuel and the oxidant to the catalyst layer 110. A conductive substrate is used as the electrode substrate 120, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (a porous film composed of a metal cloth in a fibrous state). Or a metal film formed on a surface of a cloth formed of polymer fiber (referred to as metalized polymer fiber), but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin for the electrode substrate 120 because it can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene or copolymers thereof can be used.

In addition, the electrode substrate 120 may further include a microporous layer (not shown) to enhance the reactant diffusion effect. These microporous layers are generally conductive powders having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, and carbon nanohorns. -horn or carbon nano ring.

Meanwhile, the catalyst layer of the cathode electrode 200 includes a catalyst and a binder resin.

The catalyst serves to promote a reduction reaction of an oxidant such as oxygen in the cathode electrode 200, platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy ( M is a transition metal selected from the group consisting of Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh and combinations thereof) and combinations thereof The catalyst of choice can be used. Specific examples include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, Pt / Ru / Sn / W and combinations thereof may be used.

Such a platinum-based catalyst may be used as a metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbonaceous materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotube, carbon nanofiber, carbon nanowire, carbon nanoball, or activated carbon may be used, or alumina, silica, titania Inorganic fine particles such as zirconia and the like may be used, but in general, carbon-based materials are widely used.

The binder resin and the electrode substrate 220 may be the same as those used in the anode electrode 100 in the cathode electrode 200.

The polymer electrolyte membrane 300 functions as an ion exchange to transfer hydrogen ions generated in the catalyst layer of the anode electrode 100 to the catalyst layer of the cathode electrode 200, and is made of a polymer resin having hydrogen ion conductivity. Representative examples thereof include a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain.

Representative examples of the polymer resin include a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer and a polyether ketone Polymers, polyether-etherketone-based polymers, polyphenylquinoxaline-based polymers or copolymers thereof, more preferably poly (perfluorosulfonic acid) (generally marketed as Nafion), poly (purple) Fluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5, 5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole), poly (2,5-benzimidazole) or copolymers thereof.

In the hydrogen ion conductive group of the hydrogen ion conductive polymer, H may be substituted with Na, K, Li, Cs or tetrabutylammonium. In case of replacing H with Na in the ion-exchange group of the side chain terminal, NaOH is substituted for the preparation of the catalyst composition, and tetrabutylammonium hydroxide is used when tetrabutylammonium is used. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The stack includes one or more membrane-electrode assemblies described above and separators located on both sides of the membrane-electrode assembly. The separator not only functions as a support, but also serves as a conductor connecting the anode electrode 100 and the cathode electrode 200 in series, and the surface of the separator prevents the oxidant and the fuel necessary for the reaction of the fuel cell. Preferably, a flow channel for supplying the anode electrode 100 and the cathode electrode 200 of the electrode assembly is formed.

As the separator, a metal, graphite, or carbon-resin composite may be used. The metal may be stainless steel, aluminum, titanium, copper, or an alloy thereof, and the like, and the carbon-resin composite may include epoxy resins, ester resins, vinyl ester resins, urea resins, and the like. A composite of a resin selected from the group consisting of combinations with a carbon-based material such as graphite may be used. However, the separator of the present invention is not limited thereto.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

Fabrication of the membrane-electrode assembly Example  1 to 3, Comparative example  One)

A catalyst slurry was prepared by adding carbon fibers to PtRu Black used as the anode electrode catalyst. Carbon fiber used VGCF (VGCF ^® -H, see Figure 2) of Showa Denko. VGCF was dispersed by sonication using an excess of isopropanol as a dispersant to disperse the carbon fibers. After the VGCF dispersion was added to the mixture of Pt Black and Nafion solution and stirred to prepare a catalyst slurry for the anode electrode. The amount of VGCF added was changed to 0% (Comparative Example 1), 2% (Example 1), 4% (Example 2), 6% (Example 3) based on the weight of the PtRu Black catalyst.

5 wt% PTFE (poly-tetrafluoroethylene) treated carbon paper (TGP-H-060, Toray Co.) was used as a support layer of the anode electrode. The catalyst was prepared by mixing PtRu Black (HiSpec 6000, Johnson Matthey) in a weight ratio of 90:10 with Nafion solution to prepare a slurry, and applying a brush to 6 mg / cm ² based on PtRu Black.

Carbon paper (Sigracet GDL 35BC, SGL) was used as the support layer of the cathode electrode 200, and the catalyst was mixed with Pt Black (HiSpec 1000, Johnson Matthey) in a weight ratio of 93: 7 with Nafion solution to prepare a slurry. Black was applied by brushing 5mg / cm ² . As the polymer electrolyte membrane, Nafion115 (Du Pont) was used. Membrane-Electrode Assembly (MEA) was fabricated by hot pressing at 135 ° C for 10 minutes at a pressure of 100 kg / cm ² per unit area. The MEA area was 9 cm ² .

Unit battery performance evaluation

In order to evaluate the performance of the unit cell, the MEA prepared by the above method was combined into a unit cell, and then mounted in the unit cell performance evaluation device. 2 M of methanol was 1.2cc / min on the anode electrode side and air on the cathode electrode side. Was injected at 350 cc / min. Unit cell performance was measured at 60 ^° C.

The overvoltage of the anode electrode was measured at a temperature range of 30 to 80 ^oC by injecting hydrogen at 100 cc / min to achieve dynamic hydrogen electrode conditions at 1.2 cc / min with 2 M methanol on the anode side.

Morphology  Electrode structure analysis through observation and pore measurement

Scanning Electron Microscopy (Hitachi S-4700, EMAX) was used to observe the application state of the carbon fiber in the anode electrode catalyst. The cross section of the catalyst layer was observed by brushing the catalyst layer to carbon paper (TGP-H-060, Toray Co.) used as the anode electrode support layer.

In addition, pore analysis was performed to investigate the structural change of the catalyst layer added with VGCF. Pore analysis was performed by mercury pore analysis (Auropore IV 9500, Micromeritics).

Cyclic Current Voltage Method  Analysis of Electrochemical Characteristic of Electrode by Measuring Electrode and Impedance

The electrochemical change of VGCF added to the catalyst layer was analyzed by cyclic voltammetry and AC impedance method.

In the cyclic voltammetry, in order to obtain a current voltage curve for the anode electrode, hydrogen is injected at 100 cc / min into a unit cell cathode electrode of 60 ^° C. and water is circulated to the anode electrode, thereby providing a voltage range of 0.1 to 1.2 V. The current was measured at a voltage scan rate of 20 mV / sec at. In the AC impedance method, 2M methanol is injected at 1.2 cc / min into the unit cell anode electrode at 60 ^o C, and hydrogen is injected into the cathode at 100 cc / min to achieve dynamic hydrogen electrode conditions. The frequency range is 5 kHz to 50 mHz. The impedance was measured at a perturbation potential of 10 mV.

Experiment result

1) unit battery performance

The unit cell performance measured for each VGCF addition ratio is shown in FIG. 3. The performance of the unit cell was improved when VGCF was added 2, 4% of the PtRu Black weight, and the performance was maximized when 2% was added. At a higher VGCF 6% addition rate, the performance was lower than without addition.

In order to confirm the effect of the anode electrode catalyst to which the VGCF is added, the result of measuring the overvoltage of the anode electrode while changing the temperature (30 ° C, 40 ° C, 50 ° C, 60 ° C, 70 ° C, 80 ° C) is shown in FIG. 4. . As shown in the performance evaluation results of FIG. 3, when the 2, 4 wt% VGCF was added to the anode, the anode overvoltage was found to be less. In particular, at 2% addition, the overvoltage was lower than at all the measured temperatures, and at low temperature ranges of 30 to 50 ^o C and at low current densities, all the anode electrodes with fibers were compared with the non-anode electrodes. This was measured low.

2) Of catalyst bed Morphology  And pore changes

5 is VGCF 0%. Photo showing SEM image (left) of anode electrode electrode layer and SEM image (right) of anode electrode catalyst layer when 2%, 4%, 6% ((a), (b), (c), (d)) were added to be. It can be seen that VGCF is relatively evenly distributed in the catalyst bed at all addition ratios. As the proportion of the VGCF added increased, the thickness of the catalyst layer also increased (see left side of FIG. 5), but the structure of the catalyst layer changed such that a space was formed between the aggregates of the catalyst particles due to fiber addition (see right side of FIG. 5). .

In addition, the distribution and the porosity of the catalyst layer to which the VGCF is added by using a pore analysis method are shown in Figure 6 and Table 1. The high peak observed in the region of 1000 nm or more is the pore distribution represented by the space between the carbon fibers (Polyacryolonitrile-based carbon fibers) constituting the catalyst coated carbon paper (TGP-H-060). It should be noted that the pore distribution below 1000 nm increased with increasing amount of VGCF added. The addition of VGCF caused structural changes in the PtRu catalyst layer, indicating an increase in pore distribution in certain regions. That is, as the fibers are added to the catalyst layer, pores of 1000 nm or less increase due to the spaces formed, thereby improving mass transfer in the catalyst layer, and increasing the utilization efficiency of the catalyst by reducing the aggregate size of the catalyst particles. Can be.

TABLE 1

VGCF content Overall porosity (%) Porosity between 100 and 2000 nm (%) 0 % 52.05 4.24 2 % 53.97 5.78 4 % 53.44 7.09 6% 56.66 8.16

3) Of catalyst bed  Change of electrochemical properties

The electrochemical effects of the anode electrode catalyst layer by VGCF addition are shown in FIG. 7, Table 2 and FIG. 7 and Table 2 show the analysis results of the anode electrode by cyclic voltammetry. When the addition rate of VGCF was increased to 4%, the electrochemically active area of the capacitance and hydrogen oxidation region by the electric double layer also increased, and slightly decreased again at the 6% addition rate. Similar to This means that the relative proportion of Nafion ionomer in the catalyst layer decreased as the ratio of VGCF addition increased, but the interface between the catalyst and Nafion and the electrochemical active area of the catalyst increased. In other words, as the size of the catalyst particles becomes smaller due to fiber addition, more electrochemically active areas of the catalyst are exposed, and the interface between the catalyst and Nafion is also increased.

TABLE 2

VGCF content Relative EAS 0 % One 2 % 1.28 4 % 1.37 6% 1.14

8 is a graph showing the change of the AC impedance with the addition of VGCF measured at 0.5V. 8 shows that the impedance of the anode electrode does not change significantly when VGCF is added to the anode electrode catalyst. Although the electrical conductivity of VGCF is known to be very high, it is still lower than that of the metal platinum-ruthenium. Nevertheless, it can be seen that the addition of VGCF does not significantly affect the electrical resistance, ion resistance and electron transfer resistance of the electrode.

1 is a view schematically showing a membrane-electrode assembly of a direct methanol fuel cell according to an embodiment of the present invention.

2 is a micrograph of the VGCF used for the preparation of the membrane-electrode assembly of Examples 1-3 and Comparative Example 1. FIG.

3 is a graph showing the results of evaluation of unit cell performance measured for each VGCF addition ratio.

4 is a graph illustrating a result of measuring an overvoltage of an anode electrode while changing temperature.

5 shows GGCF 0%. SEM image (left) of the anode electrode layer and SEM image (right) of the anode catalyst layer when 2%, 4%, and 6% ((a), (b), (c) and (d)) were added, respectively.

6 is a graph showing the pore distribution of the electrode layer according to the addition of VGCF obtained by the mercury pore method.

7 is a current voltage curve of an anode electrode according to the addition of VGCF.

8 is a graph showing the change of the AC impedance with the addition of VGCF measured at 0.5V.

Claims (16)

An anode electrode and a cathode electrode positioned to face each other and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, The anode electrode and the cathode electrode includes an electrode substrate and a catalyst layer positioned on the electrode substrate, The anode electrode catalyst layer is a membrane-electrode assembly of a direct methanol fuel cell, characterized in that it comprises a catalyst, vapor-grown carbon fiber and a binder resin. The method of claim 1, The anode electrode catalyst layer is a membrane-electrode assembly of a direct methanol fuel cell, characterized in that containing 2 to 4% by weight of the vapor-grown carbon fiber relative to the catalyst weight. The method of claim 1, The binder resin is a membrane-electrode assembly of a direct methanol fuel cell, characterized in that the ion conductive binder resin containing Nafion. The method of claim 3, The anode electrode catalyst layer further comprises a binder resin selected from the group consisting of carbon black, polytetrafuluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and styrene butadiend rubber (SBR). . The method of claim 1, The vapor-grown carbon fiber has a diameter of 50 to 500 nm, an aspect ratio of 10 or more, an electrical conductivity of 100 S / cm or more, and a true density of 1.5 g / ml or more. Electrode assembly. The method of claim 1, The anode electrode 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 membrane-electrode assembly of a direct methanol fuel cell comprising a catalyst selected from the group consisting of a combination thereof. . The method of claim 1, The cathode electrode 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 membrane-electrode assembly of a direct methanol fuel cell comprising a catalyst selected from the group consisting of a combination thereof. . The method of claim 1, The polymer electrolyte membrane is a membrane-electrode of a direct methanol fuel cell comprising a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups, and derivatives thereof in the side chain thereof. assembly. The method of claim 8, The polymer resin may be a fluorine 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, a poly Membrane-electrode assembly of a direct methanol fuel cell, characterized in that selected from the group consisting of ether ether ketone polymer, polyphenylquinoxaline polymer and copolymers thereof. 10. A stack of direct methanol fuel cells comprising the membrane-electrode assembly according to claim 1. Adding gaseous growth carbon fibers to the excess dispersion solvent and then dispersing the mixture using ultrasonic decomposition; Preparing a catalyst slurry by mixing the prepared vapor-grown carbon fiber dispersion with a catalyst and a binder resin; And A method for forming an anode catalyst layer of a direct methanol fuel cell, comprising applying the catalyst slurry to an electrode substrate. The method of claim 11, The dispersion solvent is a direct methanol fuel cell, characterized in that selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol and a mixture thereof Anode catalyst layer formation method. The method of claim 11, The vapor-grown carbon fiber is an anode catalyst layer forming method of a direct methanol fuel cell, characterized in that added to 2 to 4% by weight based on the weight of the catalyst. The method of claim 11, And the binder resin comprises Nafion, an ion conductive binder resin. The method of claim 14, Formation of the anode catalyst layer of the direct methanol fuel cell, characterized in that the binder slurry selected from the group consisting of carbon black and PTFE (polytetrafuluoroethylene), PVDF (polyvinylidene fluoride) and SBR (styrene butadiend rubber) is further added when preparing the catalyst slurry Way. The method of claim 11, The vapor-grown carbon fiber has a diameter of 100 to 300 nm, an aspect ratio of 10 or more, an electrical conductivity of 100 S / cm or more, and a true density of 1.5 g / ml or more, an anode catalyst layer of a direct methanol fuel cell Formation method.

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