KR100761523B1 - Carbon slurry composition for preparation of gas diffusion layer for fuel cell - Google Patents

Abstract

The present invention relates to a carbon slurry composition used in the production of a gas diffusion layer for a fuel cell, and a method for manufacturing the same, comprising a carbon powder, a dispersant, a fluororesin, and a secondary aqueous polymer resin, so that no pores appear in the microporous layer. A uniformly distributed gas diffusion layer may be prepared to allow fuel and reactant gas to be smoothly and uniformly supplied to the catalyst layer and to increase the utilization of the catalyst.

Gas diffusion layer, microporous layer, carbon slurry composition, dispersant, fluoro resin

Description

Carbon slurry composition for preparation of gas diffusion layer for fuel cell

1 is a flowchart of a method of preparing a carbon slurry composition according to Example 1 of the present invention.

2 is a flowchart of a method of preparing a carbon slurry composition according to Example 2 of the present invention.

3 is a flowchart of a method of preparing a carbon slurry composition according to Example 3 of the present invention.

4 is a flowchart of a conventional method for producing a carbon slurry composition.

FIG. 5 is a micrograph (40 times) of a surface of a gas diffusion layer for a fuel cell manufactured using a carbon slitter composition according to Examples and Comparative Examples. FIG.

6 is a performance graph of the membrane electrode assembly according to the Example and Comparative Example.

The present invention relates to a carbon slurry composition used in the production of a gas diffusion layer for fuel cells and a method for producing the same, and more particularly to a carbon slurry capable of producing a gas diffusion layer for fuel cells having a uniform thickness, no cracks and excellent reproducibility. It relates to a composition and a method for preparing the same.

A fuel cell is a device that produces electric energy by electrochemically reacting fuel and oxygen. Unlike thermal power generation, a fuel cell does not undergo a Carno cycle, and thus its theoretical power generation efficiency is very high. In addition, since NO _x and CO ₂ emissions and noise are lower than thermal power generation, the fuel cell is an environmentally friendly power generation device.

Fuel cells can be classified into PEM (Polymer Electrolyte Membrane), Phosphoric Acid, Molten Carbonate, Solid Oxide, etc. Depending on the electrolyte used, the operating temperature of the fuel cell and the material of the components are different. In addition, the fuel cell is an external reforming type for converting fuel into a hydrogen-enriched gas through a fuel reformer and supplying the anode to the anode and a direct oxidation type or an internal reforming type for supplying fuel directly to the anode according to the fuel supply method to the anode. It can be divided into. Natural fuels, methanol, and the like are generally used as fuels used in fuel cells, but other hydrocarbon fuels or derivatives thereof may be used.

Among the fuel cells, polymer electrolyte membrane fuel cells (hereinafter, abbreviated as "PEMFC") have lower operating temperature, higher efficiency, higher current density, higher output density, and higher startup time than other types of fuel cells. Short and fast response to load changes. In addition, since the polymer membrane is used as the electrolyte, there is no need for corrosion and electrolyte control, the design is simple, the manufacturing is easy, and the volume and weight are smaller than those of the phosphate fuel cell having the same operation principle. Compared with the secondary battery developed as a power source for electric vehicles, the specific energy density of the polymer electrolyte membrane fuel cell is 200 Wh / kg to thousands of Wh / kg or more, and has a value of 200 Wh / kg or less. It has a higher advantage. In addition, in terms of the charging time, the lithium battery requires about 3 hours of charging time, whereas the fuel cell power to be developed in this study has a big advantage because the fuel injection time is only a few seconds. . Accordingly, research and development of polymer electrolyte membrane fuel cells has been actively conducted worldwide as transportation power sources, mobile and emergency power sources, and military power sources, which replace batteries of electric vehicles.

In the fuel cell, the electrode causing the electrochemical reaction is composed of a gas diffusion layer and a catalyst layer. The gas diffusion layer serves to connect the electric current generated during the electrochemical reaction with an external electric circuit, having a pore and pores, and a material capable of smoothly accessing the fuel layer and the reactor gas to the catalyst layer. In general, carbon paper or carbon fiber fabric is used as the substrate of the gas diffusion layer. Carbon species or carbon fiber fabrics are produced by injecting carbon made from a polymer such as PAN at a high temperature of 2000 ° C. or higher into a fiber form, and then compressing it to produce a thin sheet of paper, or making the fiber into a fabric again through a complex weaving process. do. The process of producing carbon paper in the form of a sheet is a very difficult and difficult process, it is difficult to maintain a constant porosity and mechanical strength inside the paper. In the cross section of the commercialized carbon paper, the porosity is very different from one part to the other. Especially, the application of several nano sized catalysts on top of the carbon paper is a significant factor that causes a large number of catalysts to enter the porous carbon species and reduce the reaction efficiency of the catalyst. In addition, due to the irregular porosity, the voltage drop largely occurs when the electrons of the fuel cell generated in the region of high current flow through the external circuit. Carbon fiber fabrics have a much larger porosity than carbon paper, so this phenomenon occurs more and can not be made thinner.

In order to compensate for this, a method of manufacturing a gas diffusion layer by forming a micro-porous layer (MPL) including carbon particles on a porous substrate has been developed, but irregular cracks are found on the surface of the formed MPL. There is a problem. Irregular cracks on the surface of the MPL cause irregular distribution of large pores in the gas diffusion layer, thereby preventing smooth and uniform supply of fuel and reactant gases, and decreasing the efficiency of the catalyst by allowing the catalysts applied on the gas diffusion layer to enter the gas diffusion layer. Falling can be a major cause.

International patent WO 2003/054994 (Korean Patent Publication No. 10-2004-0071725) discloses an aqueous coating composition comprising carbon particles, at least one high fluorinated polymer and at least one amine oxide surfactant, Korean Patent Application No. 10-2004-7009514 discloses combining carbon and one or more surfactants in an aqueous fluid, typically by high shear mixing, to prepare a precomposition, wherein one or more highly fluorinated polymers are prepared by low shear mixing. A method of preparing a gas diffusion layer for an electrochemical cell is introduced, which comprises adding to the composition to prepare a coating composition, and applying the coating composition to the electrically conductive porous substrate, typically by a low shear coating method.

In addition, Korean Patent Application No. 10-2004-7009592 discloses a method of manufacturing a gas diffusion layer by compressing the gas diffusion layer applied on the plain weave carbon fiber fabric of the electrically conductive porous substrate at a compression rate of 25% or more.

The above methods are to prepare a carbon slurry by mixing PTFE and the like in a carbon dispersion containing carbon and a surfactant, the coating method is limited because the resulting slurry has a high viscosity of 100,000 cps or more. In addition, before firing the carbon slurry coated on the carbon substrate, since the MPL on the substrate does not have a bonding force with the substrate or in the MPL, a process is performed in which the MPL is impregnated into the substrate to maintain the skeleton by a method such as calendering after application. do. In this case, however, it is impossible to control the cracks generated on the surface of the substrate, and it is not possible to suppress the infiltration of MPL into the substrate.

In addition, as described in Korean Patent Application No. 10-2004-7009592, when applying a carbon slurry to a carbon substrate and then pressing the substrate and MPL through calendering, the substrate such as carbon species or carbon felt is originally compressed while having about 40 to 60%. The mechanical strength that was present drops and the porosity changes. In particular, in the case of using carbon fibers, the MPL has a binding force with the substrate only after pressing the MPL again through hot pressing at a temperature of 132 ° C. The gas diffusion layer fabricated in this way has a large amount of macro-crack on the surface, resulting in non-uniform diffusion of the reaction gas, thereby degrading fuel cell performance. MPLs on substrates are known to contribute significantly to fuel cell performance by forming multiple layers of different structures and materials, depending on the application or whether it is an anode or a cathode. However, in order to form MPL of one layer and MPL of another layer as in the conventional method, each layer must be subjected to a process such as application-drying-pressing-application-drying-pressing-heat treatment. It is very difficult to give different porosities and different structures. In addition, the MPL of the first layer formed on the substrate during the pressing process is impregnated with a substantial portion of the substrate, which greatly reduces the porosity of the original substrate, it is difficult to reproducibly control the amount of impregnation, the substrate of the fuel cell is hard It is hard to apply because the carbon paste to be applied has hard properties due to the activation of PTFE.

Therefore, the technical problem to be achieved by the present invention is to provide a carbon slurry composition that can be used in the production of a gas diffusion layer that can be improved in the utilization rate of the catalyst by the pores are regularly distributed without cracks on the MPL surface.

In addition, the second technical problem to be achieved by the present invention is to provide a method for producing the carbon slurry as described above.

In the present invention to achieve the above object

A carbon slurry composition is provided comprising a carbon powder, a dispersant, an aqueous polymeric resin, and a fluoro resin suspension.

According to one embodiment of the present invention, the dispersant may include 1 to 50 parts by weight, 5 to 50 parts by weight of the aqueous polymer resin, and 5 to 100 parts by weight of the fluoro resin, based on 100 parts by weight of the carbon powder.

According to another embodiment of the present invention, the dispersant may be at least one selected from the group consisting of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

According to another embodiment of the present invention, the aqueous polymer resin may be a polymer resin which may be carbonized in an air or oxygen atmosphere at a temperature of 250-400 ° C.

According to another embodiment of the invention the fluoro resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) , Polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE) and polyfluorovinylidene (PVDF).

In a second aspect of the present invention there is provided a method of producing a carbon slurry composition comprising mixing a carbon powder, a solvent, a dispersant and an aqueous polymer resin to prepare a preliminary composition and adding a meltable fluoro resin to the preliminary composition. Is provided.

According to an embodiment of the present invention, the preparing of the preliminary composition may include dispersing by adding a solvent to the carbon powder, further dispersing by adding a dispersant to the dispersion, and adding a water-based polymer resin to the dispersion. It can be made in the step of making.

According to another embodiment of the present invention, the preparing of the preliminary composition may include adding and dispersing a solvent in a dispersant, adding and dispersing carbon powder in the mixture, and adding a water-based polymer resin to the dispersion to prepare a preliminary composition. It can be done in the making step.

According to another embodiment of the present invention, the preparing of the preliminary composition may include adding and mixing a solvent in a dispersant, adding and mixing an aqueous polymer resin in the mixture, and dispersing by adding carbon powder to the resultant. It may consist of making a preliminary composition.

 The gas diffusion layer prepared using the carbon slurry composition according to the present invention does not show any macro cracks or micro cracks after drying, so that the pores are regularly distributed and the utilization rate of the catalyst may be improved.

Hereinafter, the present invention will be described in more detail.

The carbon slurry composition used for preparing a gas diffusion layer for a fuel cell according to the present invention includes a carbon powder, a dispersant, an aqueous polymer resin, and a meltable fluoro resin.

The dispersant for dispersing the carbon powder may include at least one of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant which is excellent in compatibility with the fluoro resin and capable of dispersing the carbon powder. have. Specific examples include cationic surfactants such as alkyltrimethylammonium salts, alkyldimethylbenzylammonium salts and phosphate amine salts; Anionic surfactants such as polyoxyalkylene alkyl ethers, polyoxyethylene derivatives, alkylamine oxides and polyoxyalkylene glycols; Amphoteric surfactants such as alanine, imidazolium betaine, amidepropyl betaine and aminodipropionate; Nonionic surfactants, such as alkylaryl polyether alcohols, etc. can be used, It is not limited to the kind listed. Among the commercialized products, anionic surfactants may include Clariant's HOSTAPAL, EMULSOGEN, BYK's Dispersbyk, TEGO's Dispers, and the like. Triton X-100 may be used as the nonionic surfactant. The dispersant to be used may be any substance which can be thermally decomposed and removed at a temperature of 250 to 400 ° C.

The water-based polymer resin may provide a bonding force to the carbon slurry produced by connecting the carbon and carbon of the carbon powder, thereby improving the characteristics of the slurry without affecting the electrode reaction of the fuel cell.

In the dispersion preparation process, the solvent, the dispersant, and the aqueous polymer resin may be added at the same time or added sequentially.

The aqueous polymer resin may be removed by carbonization in an air or oxygen atmosphere at a temperature in the range of 250 to 400 ° C., and the remaining amount does not affect the reaction of the fuel cell.

For example, polyethers consisting of polyethylene oxide, polyethylene glycol, polyacetaldehyde, and the like, polysulfides, polyesters, polycarbonates, ethylene-propylene-elastomers (EPDM), polyethylene, polypropylene, PVC, and It may include one or more of polyvinyls made of polyvinyl fluoride and the like, cellulose, cellulose derivatives, and polysacaccharides made of starch series.

The fluoro resin may be polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE ), Tetrafluoroethylene-ethylene copolymer (ETFE) and polyfluorovinylidene (PVDF).

Carbon powder is porous and electrically conductive, for example, active carbon powder (active carbon), active carbon fiber (active carbon fiber), carbon black (carbon black), carbon aero-sol, carbon nanotubes (carbon nanotube), carbon nanofiber (carbon nanofiber), carbon nanohorn (carbon nanohorn) powder, or natural or synthetic graphite (graphite) powder or mixtures thereof may be used, but is not limited to the above items. There is no particular limitation on the average particle size, surface area, average pore size, etc. of the carbon powder. However, if the average particle size of the carbon powder is too small, smooth access of the fuel and the reactor gas to the catalyst layer may be prevented, and the ability to discharge carbon dioxide and water generated during the reaction may be reduced. On the other hand, if the average particle size of the carbon powder is too large, the macropores may be formed to reduce the fuel carrying capacity, the interface resistance between the electrons and the current collector generated during the reaction may be excessively increased. In consideration of this point, the average particle size of the carbon powder may be about 20 nm to about 5000 nm.

If the specific surface area of the carbon powder is too small, not only the supporting capacity of the fuel may be lowered, but also the contact resistance with the catalyst may be increased. If the carbon powder is too large, the reaction product may not be smoothly discharged due to excessive microporosity. In view of this, the specific surface area of the carbon powder may be about 20 m 2 / g to about 2000 m 2 / g, more preferably, about 50 m 2 / g to about 1500 m 2 / g, Even more preferably, it may be about 80 m 2 / g to about 800 m 2 / g.

In the carbon slurry composition according to the present invention, the dispersant is preferably 1 to 50 parts by weight, 5 to 50 parts by weight of the aqueous polymer resin, and 5 to 100 parts by weight of the fluoro resin, based on 100 parts by weight of the carbon powder. More preferably, it is 5-30 weight part of dispersing agents, 10-30 weight part of aqueous polymer resins, and 10-30 weight part of fluororesins with respect to 100 weight part of carbon powders.

The content of the dispersant and the water-based polymer resin can vary greatly depending on the type, specific surface area and structure of the carbon used in the slurry. For example, in the case of carbon having a large specific surface area such as Vulcan XC-72, since a large amount of polymer resin may be impregnated in the fine pores, a large amount of water-based polymer resin is required and a large amount of dispersant is difficult to disperse. Is needed. However, the use of acetylene black with a small specific surface area requires a smaller amount of aqueous polymer resin and dispersant.

 If the fluoro resin is less than 5 parts by weight, the binding strength of the slurry is lowered, the mechanical strength is lowered, if more than 100 parts by weight may increase the electrode resistance.

The carbon slurry composition according to the present invention may comprise two or more solvents.

As a solvent, in addition to the basic solvents of water, n-propanol and isopropanol, some high boiling point solvents such as ethylene glycol, propylene glycol, DMSO, NMP, and butyl acetate can be mixed and used, and most preferably, It is to mix part of the point solvent.

Carbon slurry composition according to the present invention comprises the steps of preparing a preliminary composition by mixing a solvent, a dispersant and an aqueous polymer resin to the carbon powder; And it may be prepared by a method comprising the step of mixing by adding a fluoro resin suspension to the preliminary composition.

That is, by adding a solvent to the carbon powder to disperse, further dispersing by adding a dispersant to the dispersion, adding a water-based polymer resin to the dispersion to make a preliminary composition, by adding a fluoro resin to the preliminary composition A method comprising mixing; Adding and mixing a solvent to a dispersant, adding and dispersing carbon powder to the mixture, adding a water-based polymer resin to the dispersion to make a preliminary composition, and adding and mixing a fluoro resin to the preliminary composition. Method comprising a; And adding and mixing a solvent to a dispersant, adding and mixing an aqueous polymer resin to the mixture, adding and dispersing carbon powder to the resultant to make a preliminary composition, and adding and mixing a fluoro resin to the preliminary composition. It is a method comprising the steps.

A method of preparing a gas diffusion layer using the carbon slurry compositions prepared by the above three methods is shown in sequence in FIGS. 1 to 3.

When mixing to prepare the preliminary composition, the mixing speed may be 500 to 10000 rpm. If the speed is slower than 500rpm, the carbon powder is not effectively dispersed, and if the speed is faster than 10000rpm, excess heat may be generated in the slurry, thereby changing the composition of the slurry.

The fluidity and viscosity vary depending on the amount of solvent added when the carbon slurry composition is prepared, and a carbon slurry composition having a viscosity of about 1 to 500,000 cps can be prepared according to the coating method.

  When the fluoro resin is added and mixed to the preliminary composition, the mixing speed may be 10 to 500 rpm. If the speed is slower than 10 rpm, the fluorine resin may not be properly mixed in the slurry. If the speed is faster than 500 rpm, the fluoro resin may be fibrized by the shear force.

The carbon slurry is applied to a carbon substrate and then dried to form MPL to prepare a gas diffusion layer. Carbon slurry coating and drying may be repeated two or more times to form a multi-layer MPL. At this time, the carbon base material is preferably dipped in a water repellent solution and dried to be water repellent.

Examples of the carbon substrate include carbon paper, carbon fiber, carbon felt, carbon sheet, and the like, but are not limited thereto.

Water repellents capable of forming water repellent capillary gas passages include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychloro A fluoro resin suspension containing at least one selected from the group consisting of trifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE) and polyfluorovinylidene (PVDF) may be used as the water repellent solution. . The substrate subjected to the water repellent treatment is not baked before the primer layer is applied.

The content of the water repellent material in the substrate may preferably be about 1% to about 60% by weight, more preferably about 2% to about 45% by weight, even more preferably about 5% to about 40% by weight. Weight percent.

The carbon slurry composition may be of the same composition or of a different composition, form a uniform layer having a thickness of 1 to 200㎛, and the thickness of the gas diffusion layer is increased without the micro-cracks generally occurring The deviation can be minimized to within 5%.

The coating method may be applied by a general coating method, for example, a die, comma, bar, gravure, knife coating, or the like.

The gas diffusion layer of the present invention may typically have an electrical resistivity (in-plane and thru-plane resistance) of about 1 Ω / cm or less, and more preferably about 0.1 Ω / cm or less. It may have a resistance of even more preferably about 0.01 Ω / cm or less.

After coating and drying the carbon slurry composition, the carbon slurry is placed in an oven at 250 to 400 ° C. for heat treatment. At this time, some of the fluoro resin impregnated on the substrate and the fluoro resin of MPL formed thereon are dissolved and have a bonding force, and the water-based polymer resin, dispersant, etc. added to the carbon slurry composition are all decomposed and removed or carbonized during the heat treatment process. do.

The gas diffusion layer prepared from the carbon slurry composition of the present invention has a smaller interfacial resistance than the gas diffusion layer prepared from the conventional carbon slurry composition. In the conventional gas diffusion layer manufacturing process shown in FIG. 1, a carbon slurry composition is obtained by mixing a carbon powder, a solvent, and a PTFE suspension, and the substrate is impregnated in a water repellent solution, followed by drying and heat treatment, ie, firing, to apply the carbon slurry composition. And a dry-firing process to prepare a gas diffusion layer. Since the carbon slurry having a high viscosity is applied and calcined again on the substrate which has already been calcined, the fluororesins of the substrate and the MPL have different characteristics. Due to the high interface resistance has a disadvantage.

However, the present invention uses a carbon slurry composition comprising a water-based polymer resin, and after the substrate is impregnated in the water repellent solution, the process of sequentially applying and drying the carbon slurry composition on a dry substrate without going through a sintering process to repeat the multilayer Since the firing is performed at a time after forming the MPL of the structure, the polymer resin of the base material and the fluoro resin of each MPL are connected in a network, so that the interface resistance is small and the penetration resistance of the electrode is very small. This increases the reaction efficiency of the electrode and increases the performance of the fuel cell.

 In the present invention, there is also provided a fuel cell electrode comprising a gas diffusion layer and a catalyst layer prepared from the carbon slurry composition. The fuel cell electrode refers to an anode and a cathode used in the fuel cell. Oxidation reaction of fuel occurs in the catalyst layer of the anode, and oxygen reduction reaction occurs in the catalyst layer of the cathode. For example, the catalyst layer of anode and cathode of PEMFC or direct methanol fuel cell (DMFC) is generally a catalyst capable of causing an oxidation reaction and a reduction reaction of oxygen, respectively, and the mechanical strength of the catalyst layer after fixing the catalyst It includes a hydrogen ion conductive binder resin to maintain.

The catalyst may be a metal catalyst or a supported catalyst. By metal catalyst is meant a catalytic metal powder itself which can cause oxidation of fuel or reduction of oxygen. The supported catalyst refers to a catalyst composed of a catalyst carrier having micropores and catalytic metal particles supported in the micropores of the catalyst carrier. As the catalyst metal particles, for example, platinum powder, Pt-Ru powder, or the like may be used, but is not limited thereto. As the catalyst carrier, for example, active carbon powder, carbon nanotube powder, carbon nanohorn powder, artificial or natural carbon black, or the like can be used.

As the hydrogen ion conductive binder resin, for example, a polymer having a cation exchange group such as a sulfonic acid group, a carboxyl group, a phosphoric acid group, an imide group, a sulfonimide group, a sulfonamide group, a hydroxy group, or the like can be used. Specific examples of the polymer having a cation exchange group include trifluoroethylene, tetrafluoroethylene, styrene-divinyl benzene, α, β, β-trifluorostyrene ( α, β, β-trifluorostyrene, styrene, imide, sulfone, phosphazene, etherether ketone, ethylene oxide, polyphenylene sulfide (polyphenylene sulfide) or a homopolymer of an aromatic group (aromatic group) and copolymers (copolymer) and derivatives thereof, and the like, these polymers may be used alone or in combination. More preferably, the polymer having a cation exchange group is a high fluoropolymer in which the number of fluoro atoms is 90% or more in the total of the number of fluorine atoms and hydrogen atoms bonded to carbon atoms in the main and side chains thereof. (highly fluorinated polymer). In addition, the polymer having a cation exchange group has a sulfonate as a cation exchange group at the end of the side chain and is fluorine in the sum of the number of fluoro atoms and hydrogen atoms bonded to the carbon atoms of the main and side chains. Furnaces may contain highly fluorinated polymer with sulfonate groups, wherein the number of atoms is greater than 90%.

The catalyst layer can be prepared, for example, in the following manner. That is, (i) homogeneously dispersing the catalyst and the hydrogen ion conductive binder resin in a solvent to prepare a catalyst ink, (ii) printing, spraying, rolling, brushing (for example, In a method such as brushing), an electrode including the catalyst layer and the diffusion layer is prepared by uniformly applying the catalyst ink onto the diffusion layer and (iii) drying the resultant to form the catalyst layer.

The fuel cell provided in the present invention includes an anode cathode and a hydrogen ion conductive electrolyte membrane, wherein the anode, or the cathode, or the anode and the cathode comprises a gas diffusion layer according to the present invention.

The fuel cell of the present invention can be applied to, for example, PAFC, PEMFC, DMFC, or the like. The construction and manufacturing method of this kind of fuel cell are well known in the literature and will be readily apparent to those skilled in the art, and thus further detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the technical scope of the present invention is not limited to the following examples.

<Example>

Example 1

1000g of ultrapure water was added to Cabot's Vulcan XC-72 and mixed in a high speed mixer (2000rpm), followed by dispersant Triton X-100 and dispersed for 1 hour, followed by addition of carboxymethyl cellulose in an amount of 30g and further dispersion for 1 hour. To obtain a precomposition. 30 wt% of PTFE (30J of Dupont) was added thereto, followed by stirring for 1 hour with a low speed mixer (200 rpm) to prepare a carbon slurry composition.

Toray's TGPH-060 based on carbon was impregnated with PTFE suspension for 5 minutes and dried to obtain a PTFE content of 30% by weight. The impregnated substrate was dried in a drying oven at 80 ° C. for 1 hour, and the carbon slurry thus prepared was applied by a knife coating method to dry in an drying oven at 80 ° C. for 1 hour to be 40 μm thick after drying. The dry gas diffusion layer was placed in an oven at 350 ° C. and fired for 30 minutes.

In order to form the catalyst layer, Pt-Ru powder and Nafion were added to a mixed solvent (1: 1 weight ratio) of isopropyl alcohol and water, and then dispersed in an ultrasonic wave bath for about 10 minutes or more. Thus obtained catalyst ink was impregnated with 5 wt% PTFE in the substrate, and the anode was prepared by applying a spray coating method to the gas diffusion layer prepared in the above manner and drying. At this time, the Nafion content of the dried catalyst layer was about 10% by weight, and the catalyst loading amount of the anode was about 5 mg / cm 2.

Pt black powder and Nafion were added to a mixed solvent (1: 1 weight ratio) of isopropyl alcohol and water, and then dispersed in an ultrasonic bath for about 10 minutes or longer. The cathode was prepared by applying the catalyst ink thus obtained to 40% by weight of PTFE impregnated into the substrate and applying the same to the gas diffusion layer prepared in the above manner by spray coating. At this time, the Nafion content of the dried catalyst layer was about 10% by weight, and the amount of catalyst loading of the cathode was about 5 mg / cm 2.

The hydrogen-ion conductive polymer electrolyte membrane was prepared by treating Nafion 115 of Dupont with hydrogen peroxide and sulfuric acid to remove organic substances on the surface and to replace sodium ions in the Nafion functional group with hydrogen ions.

The prepared anode and cathode were cut to a size of 5 cm and 5 cm, and the prepared hydrogen ion conductive electrolyte membrane was cut to a size of 7 cm and 7 cm larger than the electrode. The anode catalyst layer and the cathode catalyst layer were placed in contact with the hydrogen ion conductive electrolyte membrane, and then pressurized at 100 kg _f / cm 2 at a temperature of about 140 ° C. to prepare a MEA.

The prepared MEA was mounted on a unit cell test jig to supply a 2M methanol aqueous solution to the anode at a rate of 1 ml / min using a pump, and oxygen to the cathode at a rate of 1 l / min. Under an operating condition of 50 ° C, an electronic load was connected to the unit cell to measure the voltage drop according to the current density.

Example 2

In a solution in which ultrapure water was mixed with a dispersant Triton X-100, Cabot's Vulcan XC-72 was added and mixed in a high speed mixer, and an aqueous solution of cellulose was added and stirred for 1 hour to prepare a preliminary composition. PTFE (30J manufactured by Dupont) was added to the preliminary composition to 30 wt% and stirred slowly in a low speed mixer to prepare a carbon slurry.

Abcarb ^TM 1071 HCB, a carbon fiber manufactured by Ballard Material Products, was used as the substrate for the gas diffusion layer, and the PTFE content impregnated in the substrate of the anode gas diffusion layer was 5% by weight, and the PTFE content impregnated in the substrate of the cathode gas diffusion layer. Except for 40% by weight, a gas diffusion layer and a fuel cell including the same were manufactured in the same manner as in Example 1, and the voltage drop according to the current density was measured.

Example 3

A solution of cellulose was added to a solution in which ultrapure water was mixed with the dispersant Triton X-100, mixed in a mixer, and a preliminary composition was prepared by adding Cabot's Vulcan XC-72 and mixing for 1 hour. PTFE (30J of Dupont) was added to the preliminary composition to 30 wt%, and stirred slowly in a low speed mixer to prepare a carbon slurry.

As the base material of the gas diffusion layer, GDL10AA, a carbon felt made by SGL, was used, and the PTFE content impregnated into the base material of the anode gas diffusion layer was 5% by weight, and the PTFE content impregnated into the base material of the cathode gas diffusion layer. Except for%, the same fuel cell as in Example 1 was prepared in the same manner as in Example 1, and subjected to performance tests.

Comparative example

A gas diffusion layer was prepared in the manner shown in FIG. 1, using LT-1400W coated with MPL on carbon fiber commercially available from US E-TEK Co., Ltd., which is commercially available as the gas diffusion layer of the anode, and 5% PTFE was used as the gas diffusion layer of the cathode. A fuel cell was manufactured in the same manner as in Example 1, except that SGL-10BC, which was coated with MPL, was applied to impregnated carbon felt, and the voltage drop according to the current density was measured.

<Evaluation result>

Properties for the carbon slurry compositions prepared in Examples 1 to 3 are shown in Table 1 below. Viscosity measurements were performed on LVDV II + PRO, Brookfield Viscometer Spindle No. The particle size distribution was measured at 4, 10 rpm and LS 13 320, Beckmann Coulter.

Viscosity (cPs) Particle size (㎛) D ₁₀ D ₅₀ D ₉₀ Example 1 8,000 ± 1000 0.220 0.354 1.379 Example 2 8,000 ± 1000 0.204 0.359 1.466 Example 3 8,000 ± 1000 0.201 0.359 1.462

As shown in Table 1, the carbon slurry composition prepared in Examples 1 to 3 has a viscosity of 8000 ± 1000 cPs that can be applied to a mass production process, for example, die, roll, gravure, knife coating, etc., It can be seen that reproducibility between production lots can be obtained by measuring the viscosity and particle size of the slurry by making the slurry several times.

Gas diffusion layers (a) and (b) prepared for the anodes in Examples 1 and 2, a gas diffusion layer (c) coated with carbon paste on carbon fiber of E-TEK company of Comparative Example, and a gas diffusion layer (d) of SGL company The surface photograph of is taken and shown in FIG. As shown in FIG. 5, the gas diffusion layer prepared from the carbon slurry composition of the present invention exhibits a smooth surface shape covering all the curvature of the substrate with little MPL impregnation into the carbon species or carbon fiber, and has no cracks on the surface. However, commercially available gas diffusion layers are highly moistened with MPL in the substrate, especially SGL's gas diffusion layers are up to 50% inside, and many cracks and undispersed particles appear on the surface. The cracks in the gas diffusion layer, which is responsible for the fuel supply and discharge of the reactants, exhibit a non-uniform distribution of fuel and reactants, thereby reducing the reaction efficiency due to partial degradation of the catalyst because the reaction of the catalyst layer does not appear uniformly over the entire surface. Bad effect on long life. In particular, the crack of the gas diffusion layer for the anode increases the rate at which the methanol solution crosses over to the polymer membrane and the cathode, thereby lowering the reaction efficiency and the cell voltage of the cathode, thereby greatly deteriorating the characteristics of the fuel cell.

However, the gas diffusion layer prepared by the method of the present invention allows the fuel to be uniformly distributed without cracks on the surface.

The voltage drop curves measured in Examples 1 to 3 and Comparative Examples are shown in FIG. 6.

As shown in Figure 6, it can be seen that the degree of voltage drop with increasing current density in Examples 1 to 3 is gentler than that of the comparative example. The gentle slope of the voltage drop curve means that the polymer electrolyte membrane fuel cell according to the present invention can respond to load variations more efficiently. In addition, it can be seen that the maximum current density in Examples 1 to 3 is larger than that of the comparative example. The improvement of the maximum current density is indicated by the improvement of the maximum value of the supply power. In case of using gas diffusion layer with many cracks in MPL for anode, MEA performance is deteriorated due to methanol crossover through Nafion polymer membrane. However, if MPL thickness is uniform, the thickness of catalyst layer formed on MPL is uniform. The performance of the MEA is improved because a uniform reaction can occur over.

From the above facts, the gas diffusion layer prepared from the carbon slurry composition of the present invention has a homogeneous electron conductivity that enables a smooth electrical connection with an external electric circuit, and also enables a smooth access of fuel and the reactor gas to the catalyst layer. Since it has a uniform porosity, it can be seen that the performance of the fuel cell can be improved.

The gas diffusion layer prepared by using the carbon slurry composition according to the present invention has a homogeneous electron conductivity to enable a smooth electrical connection with an external electric circuit, and also has a porosity that enables smooth access of the fuel and the reactor to the catalyst layer. Have

The carbon slurry composition of the present invention is not limited to the gas diffusion layer of a polymer fuel cell, and using the principles of the present invention, various types of fuel cells using gas diffusion layers such as phosphoric acid fuel cells, formic acid fuel cells, and dimethyl ether fuel cells may be used. Applicable to

Claims (10)

A carbon slurry composition comprising a carbon powder, a dispersant, an aqueous polymer resin, and a fluoro resin. The method of claim 1, wherein the fluoro resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychloro At least one selected from the group consisting of trifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE) and polyfluorovinylidene (PVDF). The carbon slurry composition of claim 1, wherein the dispersant is at least one selected from the group consisting of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. The carbon slurry composition of claim 1, wherein the water-based polymer resin is a polymer resin that can be carbonized in an air or oxygen atmosphere at a temperature of 250 to 400 ° C. The carbon slurry composition according to claim 1, comprising 1 to 50 parts by weight of dispersant, 5 to 50 parts by weight of aqueous polymer resin, and 5 to 100 parts by weight of fluororesin, based on 100 parts by weight of carbon powder. A method of preparing a carbon slurry comprising mixing a solvent, a dispersant, and an aqueous polymer resin with a carbon powder to prepare a preliminary composition, and adding and mixing a fluoro resin suspension to the preliminary composition. Manufacturing method. The method of claim 6, wherein the preparing of the preliminary composition comprises dispersing by adding a solvent to the carbon powder, further dispersing by adding a dispersant to the dispersion, and adding a water-based polymer resin to the dispersion to make a preliminary composition. Method comprising the steps. The method of claim 6, wherein the preparing of the preliminary composition comprises adding a solvent to the dispersant and mixing the mixture, adding and dispersing carbon powder to the mixture, and adding a water-based polymer resin to the dispersion to form the preliminary composition. Method comprising the. The method of claim 6, wherein the preparing of the preliminary composition comprises adding and mixing a solvent to a dispersant, adding and mixing an aqueous polymer resin to the mixture, and dispersing by adding carbon powder to the resultant. Method comprising the step of making. Preparing a carbon slurry composition comprising a carbon powder, a dispersant, an aqueous polymer resin and a fluoro resin, applying the carbon slurry composition onto a non-conductive / non-porous film and then drying to form a carbon layer, the non-conductive Peeling off the non-porous film and calcining the carbon layer.

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