Electrode for a polymer electrolyte membrane fuel cell and method of forming a membrane electrode assembly using the same

Abstract

Electrode for a polymer electrolyte membrane fuel cell, the electrode containing: 100 parts by weight of a carbon-supported catalyst; 20 to 80 parts by weight of a hydrogen ion-conductive polymer electrolyte binder material, based on 100 parts by weight of the carbon-supported catalyst; 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of the carbon-supported catalyst; and 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst, wherein the carbon nanofibers are added to a layer of the carbon-supported catalyst, wherein the carbon nanofibers contain at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns, and carbon nanorings having a diameter of 5 to 100 nm and a length of more than several hundred nanometers.

Description

Backgrounda) Technical area

[0001] The present disclosure generally relates to a membrane electrode assembly for a fuel cell. More specifically, it relates to an electrode for a polymer electrolyte membrane fuel cell (PEMFC) and a method of forming a membrane electrode assembly (MEA) using the same, which increases the physical durability of the fuel cell by adding carbon nanofibers and the chemical durability of the fuel cell by adding a free radical inhibitor. b) State of the art

[0002] Compared to other fuel cell types, a polymer electrolyte membrane fuel cell (PEMFC) generally exhibits several advantages, such as high energy efficiency, high current density, high power density, short start-up time, and rapid response to load changes. In particular, a PEMFC is less susceptible to pressure changes in a reactant gas and provides output power in a wide range. For these reasons, a PEMFC can be used for various applications, such as a power source for zero-emission vehicles, a stand-alone power system, a portable power source, a power source for military purposes, and more.

[0003] The PEMFC is preferably a device that generates electricity and water, which is produced by an electrochemical reaction between hydrogen and oxygen. Hydrogen, which is supplied to an anode of the PEMFC, is converted by a catalyst into hydrogen ions (protons, H + ) and electrons (e - ). The hydrogen ions are fed to a cathode through an electrolyte membrane, and the electrons are fed to the cathode. At the same time, the oxygen fed to the cathode reacts with the electrons transported from the anode to the cathode through an external conductor (e - ) and the protons migrating from the anode through the polymer electrolyte membrane to the cathode (H + ) producing water and electrical energy.

[0004] The theoretical potential is 1.23 V and the reaction scheme is as follows: Anode: H2 → 2H + + 2e- Cathode: 1 / 2 O2 + 2H + + 2e - → H2O

[0005] In the fuel cell system described above, a fuel cell stack that essentially generates electricity has a structure in which several to several tens of unit cells each having a membrane electrode assembly (MEA) and a separator (also called a bipolar plate) are appropriately stacked.

[0006] The membrane electrode assembly of the fuel cell stack preferably has a structure in which the anode (also referred to as a hydrogen electrode, fuel electrode, or oxidation electrode) and the cathode (also referred to as an air electrode, oxygen electrode, or reduction electrode) are suitably attached to the polymer electrolyte membrane arranged therebetween, and the anode and the cathode are suitably formed such that a catalyst layer comprising nano-sized platinum catalyst particles is suitably coated on a back layer of the electrode, such as a carbon paper or a carbon cloth.

[0007] Preferably and as in the conceptual illustration of the Fig. As shown in Figure 4, both the anode and the cathode contain a catalyst in which platinum is suitably supported by carbon and a polymer electrolyte binder and formed into a catalyst layer having a thickness of about 1 to 50 µm.

[0008] Furthermore, a gas diffusion layer having fine pores is suitably provided on both the anode and the cathode, which gas diffusion layer is formed by applying carbon black particles to a back layer of the electrode, such as a carbon paper or a carbon cloth, in order to supply the reactants to the membrane-electrode assembly in a uniform manner.

[0009] The gas diffusion electrode may preferably be subjected to a hydrophobic process with fluororesin in order to remove reaction by-products, such as the water (H2O) electrochemically generated in the catalyst layer of the cathode.

[0010] The membrane-electrode assembly can preferably be formed by applying a catalyst layer to a gas diffusion layer using a suitable method, and then thermally compressing the gas diffusion layer containing the catalyst layer against an electrolyte membrane. Alternatively, the membrane-electrode assembly can be formed by applying a catalyst layer to an electrolyte membrane and then bonding a gas diffusion layer to it. The gas diffusion layers in the above-described structures also serve as current collectors.

[0011] The fuel cell accordingly generates highly efficient electrical energy as well as reaction byproducts such as water by supplying hydrogen to the anode and air or oxygen to the cathode to trigger the electrochemical reaction. The electrochemical reaction between the reactants occurs preferentially in the catalyst layer contained within the fuel cell. The hydrogen ions generated by the reaction are transferred to the cathode through a polymer electrolyte (ionomer) and a polymer membrane in the catalyst layer, and the electrons are transferred to the cathode through the GDL and the bipolar plate.

[0012] The structure of the catalyst layer is appropriately determined by the electrode material, the method for forming the catalyst layer, etc. The electrode material preferably contains a platinum catalyst suitably supported by carbon and a polymer electrolyte (ionomer), and the electrode can be formed by coating a catalyst layer on a gas diffusion layer, by directly coating a catalyst layer on a membrane, or by coating a catalyst layer on a support paper and then transferring the catalyst layer to a membrane.

[0013] There are many types of carbon materials for supporting platinum, such as Ketjen black, Vulcan XC 72, acetylene black, carbon nanotubes, etc.

[0014] The conventional methods for forming the membrane electrode assembly are described here with reference to the Fig. 1 to 3. As described in Fig. 1, an electrode is suitably formed by applying, spraying, or painting a catalyst slurry onto a gas diffusion layer, and then the electrode containing the gas diffusion layer is thermally compressed to both sides of an electrolyte membrane. As shown in Fig. As shown in Figure 2, a membrane electrode assembly is formed by directly spraying, coating, or painting a catalyst slurry onto a polymer membrane and is then thermally compressed to a gas diffusion layer. As shown in Fig. 3, an electrode is further formed by spraying, coating or painting a catalyst slurry onto a support paper and transferring it to a polymer membrane, and the polymer membrane containing the catalyst layers is bonded to a gas diffusion layer.

[0015] Accordingly, in a case where the catalyst layer is formed on the gas diffusion layer, although it is advantageous for the formation of pores, it is not easy to form the membrane-electrode assembly, and this method is therefore not suitable for mass production of the membrane-electrode assembly.

[0016] Furthermore, although the method of directly forming the catalyst layer on the polymer membrane is suitable for forming small electrodes, it is difficult to form large-area electrodes due to the deformation of the polymer membrane. For example, in the method of forming the catalyst layer on the support paper and transferring the catalyst layer to the polymer membrane, the catalyst layer may crack depending on the thickness of the catalyst layer, the proportion of a binder material, and the type of catalyst, which may cause the catalyst layer to wear off during its transfer to the polymer membrane. Even if the catalyst layer is properly transferred to the polymer membrane, cracks will form in the catalyst layer, and the polymer membrane will be directly exposed to the gas supply channels, significantly reducing its performance and service life.

[0017] Accordingly, the lifetime of the membrane electrode assembly may be reduced by the polymer electrolyte, which is chemically unstable and easily decomposed.

[0018] Decomposition of the polymer electrolyte occurs both during operation and idle operation of the fuel cell and is caused directly by hydrogen peroxide, which is generated when oxygen or hydrogen permeates the polymer membrane, and by hydroxyl radicals (OH radicals) generated by the hydrogen peroxide produced in the oxygen electrode during the reaction. The generated hydroxyl radicals decompose the functional groups (-SO3H) at the end of the polymer electrolyte (binding material), thus reducing the conductivity of the hydrogen ions, thus reducing the fuel cell's performance.

[0019] US 2009 / 0081 511 A1, US 2007 / 0 248 862 A1 and US 2009 / 0 068 546 A1 disclose electrode catalysts for fuel cells.

[0020] Accordingly, there is a need in science for a new or improved polymer electrolyte membrane fuel cell (PEMFC) and methods for forming a membrane electrode assembly (MEA) using the same.

[0021] The information disclosed in the "Background" section above is intended only to facilitate understanding of the background of the invention and may therefore contain information that does not constitute prior art as already known to a person of ordinary skill in the art in this country. Summary of Revelation

[0022] The present invention provides an electrode for a polymer electrolyte membrane fuel cell (PEMFC) and a method for forming a membrane electrode assembly (MEA) using the same, in which carbon nanofibers are added to a catalyst layer to appropriately increase the mechanical strength of the catalyst layer and maintain the thickness of the catalyst layer after long-term operation, thereby appropriately preventing a decrease in the physical durability of the fuel cell, wherein cerium zirconium oxide (CeZrO4) is added to the catalyst layer as a radical inhibitor, thereby appropriately preventing a decrease in the chemical durability of the fuel cell.According to preferred embodiments of the present invention, it is possible to physically and chemically increase the performance and lifetime of the membrane electrode assembly of the fuel cell and minimize a decrease in performance after long-term operation.

[0023] The present invention provides an electrode for a polymer electrolyte membrane fuel cell, the electrode containing: 100 parts by weight of a carbon-supported catalyst; 20 to 80 parts by weight of a hydrogen ion-conductive polymer electrolyte binder, based on 100 parts by weight of the carbon-supported catalyst; 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of the carbon-supported catalyst; and 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst.wherein the carbon nanofibers are added to a layer of the carbon-supported catalyst, the carbon nanofibers containing at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns, and carbon nanorings having a diameter of 5 to 100 nm and a length of more than several hundred nanometers;

[0024] In a further preferred embodiment, the radical inhibitor may have an average particle size of 2 to 60 nm and may include at least one selected from the group consisting of cerium oxide, zirconium oxide, manganese oxide, aluminum oxide, vanadium oxide, and mixtures thereof.

[0025] In yet another preferred embodiment, the catalyst may be a platinum or platinum alloy catalyst supported on a catalyst support, wherein the catalyst support contains at least one selected from the group consisting of carbon powder, carbon black, acetylene black, Ketjen black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, carbon aerogels, carbon cryogels, and carbon nanorings.

[0026] In another aspect, the present invention provides a method for forming a membrane electrode assembly, the method including: preparing a catalyst slurry to form an electrode for a fuel cell; adding 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of a carbon-supported catalyst, to the catalyst slurry, wherein the carbon nanofibers are in a slurry state; adding 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst, to the catalyst slurry, wherein the radical inhibitor is in a solid state;Drying the final catalyst slurry prepared by adding the carbon nanofibers in a slurry state and the radical inhibitor in a solid state to the catalyst slurry and stirring the mixture to form an electrode; and thermally compressing the dried electrode to a polymer membrane, wherein the carbon nanofibers contain at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns, and carbon nanorings having a diameter of 5 to 100 nm and a length of more than several hundred nanometers.

[0027] In a preferred embodiment, the carbon nanofibers may be carbon nanotubes added in an amount of 1 to 60 parts by weight based on 100 parts by weight of the catalyst, and the radical inhibitor may be cerium zirconium oxide added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the catalyst.

[0028] In another preferred embodiment, the process of the present invention may further include milling the catalyst slurry using a planetary ball mill to reduce and uniform the particle size of the catalyst.

[0029] In yet another preferred embodiment, the final catalyst slurry may have a solids content of 5 to 30 wt.%, wherein the solids content is composed of the sum of the catalyst, the carbon nanofibers, the radical inhibitor and the ionomer.

[0030] In yet another preferred embodiment, the thermal compression may be carried out at a temperature of 100 to 180 °C and at a pressure of 50 to 300 kgf (1 kgf = 9.81 N) in 0.5 to 30 minutes.

[0031] Further aspects and preferred embodiments of the invention are discussed below.

[0032] It is understood that the term "vehicle" or "vehicular" or any similar term as used herein includes motor vehicles in general, such as passenger cars, including sports utility vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft, including various boats and ships, aircraft, and the like, as well as hybrid vehicles, electric vehicles, plug-in hybrid-electric vehicles, hydrogen-powered vehicles, and vehicles using other alternative fuels (e.g., fuels derived from resources other than petroleum). As used herein, a hybrid vehicle refers to a vehicle that utilizes two or more power sources, such as vehicles powered by both gasoline and electricity.

[0033] The above-noted features and advantages of the present invention will be apparent from, or more particularly described in, the accompanying drawings, which are incorporated in and constitute a part of the specification, and the following detailed description, which together serve to explain by way of example the principles of the present invention. Short description of the characters

[0034] The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof, which are illustrated in the accompanying figures, which are given below for illustrative purposes only and are therefore not intended to limit the present invention, in which figures: Fig. 1 to 3 are schematic diagrams illustrating conventional methods for forming a membrane electrode assembly. Fig. Figure 4 is a schematic diagram illustrating the structure of a conventional catalyst layer. Fig. 5 is a schematic diagram showing the structure of a catalyst layer containing carbon nanofibers according to an exemplary embodiment of the present invention. Fig. 6 is a schematic diagram showing the structure of a catalyst layer containing carbon nanofibers and cerium zirconium oxide as a radical inhibitor according to an exemplary embodiment of the present invention. Fig. Figure 7 is a photograph of the surface of a conventional electrode (magnified 500 times). Fig. 8 is a photograph of the surface of an electrode to which 4 parts by weight of carbon nanofibers were added based on 100 parts by weight of a catalyst according to an exemplary embodiment of the present invention (magnified 500 times). Fig. 9 is a photograph of the surface of an electrode to which 6 parts by weight of carbon nanofibers were added based on 100 parts by weight of a catalyst according to an exemplary embodiment of the present invention (magnified 500 times). Fig. 10 is a photograph of the surface of an electrode to which 8 parts by weight of carbon nanofibers were added based on 100 parts by weight of a catalyst according to an exemplary embodiment of the present invention (magnified 500 times). Fig. 11 is a photograph of the surface of an electrode to which 6 parts by weight of carbon nanofibers were added based on 100 parts by weight of a catalyst according to an exemplary embodiment of the present invention (magnified 10,000 times). Fig. 12 is an enlarged photograph of a crack in Fig. 12 (30,000x magnification). Fig. 13 is a graph comparing the running performances of the membrane electrode assemblies according to Examples and Comparative Examples. Fig. Figure 14 is a graph illustrating a change in the lifetime of an electrode to which no radical inhibitor was added. Fig. 15 is a graph illustrating a change in lifetime of an electrode to which a radical inhibitor was added according to the present invention.

[0035] It should be understood that the accompanying figures are not necessarily to scale, but rather present a somewhat simplified representation of various preferred features illustrating the basic principles of the invention. Specific embodiments of the present invention as disclosed herein, including, for example, particular dimensions, orientations, positions, and shapes, will be determined in part by the particular application contemplated and conditions of use.

[0036] In the figures, the reference numerals in all figures of the drawing designate the same or equivalent elements of the present invention. Detailed description

[0037] The present invention provides an electrode for a polymer electrolyte membrane fuel cell, wherein the electrode contains 100 parts by weight of a carbon-supported catalyst; 20 to 80 parts by weight of a hydrogen ion-conductive polymer electrolyte binder, based on 100 parts by weight of the carbon-supported catalyst; 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of the carbon-supported catalyst; and 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst. The carbon nanofibers are added to a layer of the carbon-supported catalyst.

[0038] The carbon nanofibers contain at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns, and carbon nanorings having a diameter of 5 to 100 nm and a length of more than several hundred nanometers.

[0039] In a further embodiment, the radical inhibitor has an average particle size of 2 to 60 nm and contains at least one selected from the group consisting of cerium oxide, zirconium oxide, manganese oxide, aluminum oxide, vanadium oxide and mixtures thereof.

[0040] In another embodiment, the catalyst is a platinum or platinum alloy catalyst supported on a catalyst support, wherein the catalyst support contains at least one selected from the group consisting of carbon powder, carbon black, acetylene black, Ketjen black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, carbon aerogels, carbon cryogels, and carbon nanorings.

[0041] In yet another embodiment, the platinum or platinum alloy catalyst contains platinum in an amount of 5 to 80 wt.%.

[0042] The invention also provides a method for forming a membrane electrode assembly, the method comprising preparing a catalyst slurry for forming an electrode for a fuel cell, adding 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of a carbon-supported catalyst, to the catalyst slurry, the carbon nanofibers being in a slurry state, adding 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst, to the catalyst slurry, the radical inhibitor being in a solid state, drying the final catalyst slurry prepared by adding the carbon nanofibers in a slurry state and the radical inhibitor in a solid state to the catalyst slurry and stirring the mixture, so that an electrode is formed became;and thermally compressing the dried electrode to a polymer membrane, wherein the carbon nanofibers contain at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns, and carbon nanorings having a diameter of 5 to 100 nm and a length of more than several hundred nanometers.;

[0043] Various embodiments of the present invention will be described in detail below, which are illustrated by way of example in the accompanying figures and described below. Although the invention is described in connection with exemplary embodiments, it should be understood that the present description is not intended to limit the invention to these exemplary embodiments.

[0044] In one embodiment, a first feature of the present invention is to add carbon nanotubes to a catalyst layer of an electrode for a fuel cell to increase the mechanical strength of the catalyst layer and maintain the thickness of the catalyst layer after long-term operation, thereby appropriately preventing a decrease in the physical durability of the electrode for the fuel cell.

[0045] According to an exemplary embodiment and as shown in the conceptual illustration of the Fig. 5, the carbon nanofibers are added, for example, to the catalyst layer of the electrode for the fuel cell, ie, the fuel electrode or the air electrode, so that the carbon nanofibers appropriately bind the catalyst particles contained in the electrode, thereby maintaining the strength of the catalyst layer and preventing the occurrence of cracks.

[0046] Preferably, the carbon nanotubes having the same mechanical properties can be used regardless of their type, and they include carbon nanotubes, carbon nanowires, carbon nanohorns, carbon nanorings, etc. Although various types of carbon nanofibers can be used, carbon nanofibers with higher linearity preferably produce a better effect.

[0047] The carbon nanofibers have a diameter of 5 to 100 nm and a length of more than several hundred nanometers. In certain preferred embodiments, if the diameter is less than 5 nm, it is difficult to disperse the carbon nanofibers properly. The carbon nanofibers agglomerate after dispersion, and therefore the catalyst slurry becomes uneven. Whereas if the diameter is more than 100 nm, the ability to bind catalyst particles in the catalyst layer is reduced, and the carbon nanofibers may cause physical damage to the catalyst layer. Accordingly, carbon nanofibers with a diameter of 5 to 100 nm are added to the catalyst layer.

[0048] Unlike the present invention in which carbon nanofibers with a diameter of 5 to 100 nm are added to bind the catalyst particles in the catalyst layer, carbon nanofibers with a diameter of more than 100 nm are usually used to form pores in the catalyst layer of the electrode for the fuel cell.

[0049] In a further preferred embodiment, a second feature of the present invention is to add cerium zirconium oxide (CeZrO4) as a radical inhibitor for inhibiting the hydroxyl radicals in order to prevent a decrease in the chemical resistance of the electrode for the fuel cell.

[0050] As shown in the conceptual illustration of the Fig. 6, the cerium zirconium oxide as a radical inhibitor is preferably added, for example, together with the carbon nanofibers to the fuel electrode or the air electrode, so that the hydrogen peroxide generated in each of the electrodes is decomposed with the water molecules to inhibit the generation of radicals and thus prevent decomposition of the polymer electrolyte.

[0051] Materials commonly used as radical inhibitors in the biochemical field may preferably include at least one selected from the group consisting of cerium oxide, zirconium oxide, manganese oxide, alumina, vanadium oxide, and mixtures thereof, although they are not necessarily limited as such.

[0052] According to certain preferred embodiments, in order to use the oxides as free radical inhibitors for the fuel cell, the oxides are suitably formed into nanoparticles with an average particle size of 2 to 60 nm and used in the catalyst layer to inhibit the generation of free radicals while simultaneously increasing the chemical resistance of the electrode and the polymer membrane. However, according to further exemplary embodiments, since the operating conditions of the fuel cell, such as high temperatures, high potential, etc., are harsh, the lifetime of the nanoparticles may be significantly reduced.

[0053] To physically stabilize the nanoparticles as radical inhibitors, a compound mixed with cerium and zirconium can be used as a radical inhibitor. This is because when the compound mixed with cerium and zirconium is used, the heat resistance of the cerium nanoparticles is preferably significantly increased, and thus the cerium nanoparticles are deformed and agglomerated to a lesser extent even under harsh conditions.

[0054] A structure of the electrode for the fuel cell according to an exemplary embodiment of the present invention will be described in more detail.

[0055] The electrode for the fuel cell of the present invention contains 100 parts by weight of a carbon-supported catalyst; 20 to 80 parts by weight of a hydrogen ion-conductive polymer electrolyte binder material, 1 to 60 parts by weight of carbon nanofibers, and 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst.

[0056] The carbon nanofibers contain at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, and carbon nanorings, which have a diameter of 5 to 100 nm. This is because when the diameter is less than 5 nm, it is difficult to disperse the carbon nanofibers, the carbon nanofibers are agglomerated after being dispersed, and the catalyst slurry therefore becomes uneven. Whereas when the diameter is more than 100 nm, the ability to bind catalyst particles in the catalyst layer is reduced, and the carbon nanofibers may cause physical damage to the catalyst layer.

[0057] Furthermore, according to certain exemplary embodiments, when the amount of carbon nanofibers used is less than 1 part by weight based on 100 parts by weight of the carbon-supported catalyst, it is difficult to bind catalyst particles in the catalyst layer. However, when more than 60 parts by weight are used, the carbon nanofibers interfere with mass transfer and clog the inlet and outlet for the gaseous reactants, thereby reducing the performance of the fuel cell and increasing the required amount of binding material, thus causing unnecessary waste. Accordingly, the amount of carbon nanofibers used is limited to 1 to 60 parts by weight.

[0058] Preferably, the radical inhibitor is formed into nanoparticles with an average particle size of 2 to 60 nm and is applied to the catalyst layer in such a way that it inhibits the generation of radicals and at the same time increases the chemical resistance of the electrode and the polymer membrane.

[0059] According to certain preferred embodiments, the radical inhibitor may be one selected from the group consisting of cerium oxide, zirconium oxide, manganese oxide, aluminum oxide, vanadium oxide, and mixtures thereof, although it is not limited as such. In certain embodiments, cerium zirconium oxide may preferably be used because the heat resistance of the cerium nanoparticles is significantly increased, and the cerium nanoparticles are therefore deformed and agglomerated to a lesser extent, even under harsh conditions.

[0060] Here, if the amount of radical inhibitor used is less than 1 part by weight based on 100 parts by weight of the carbon-supported catalyst, the radical inhibitor plays a negligible role. However, if more than 20 parts by weight are used, the radical inhibitor interferes with mass transfer and blocks the inlet and outlet for the gaseous reactants, thereby reducing the performance of the fuel cell and increasing the required amount of binder, thus causing unnecessary waste. Accordingly, the amount of radical inhibitor used is limited to 1 to 20 parts by weight.

[0061] A method of forming a membrane electrode assembly using the above-described electrode for the fuel cell according to the present invention will be described in more detail.

[0062] First, a catalyst slurry is suitably prepared to form the electrode for the fuel cell of the present invention.

[0063] Preferably, the catalyst slurry is prepared by mixing a carbon-supported catalyst, a polymer electrolyte (in an amount of 20 to 80 parts by weight based on 100 parts by weight of the carbon-supported catalyst), and a solvent (selected from the group consisting of water, alcohol, and a mixture thereof). Further, 1 to 60 parts by weight of carbon nanofibers and 1 to 20 parts by weight of cerium zirconium oxide as a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst, are added to the resulting mixture to prepare the final catalyst slurry.

[0064] Preferably, a platinum catalyst or a platinum alloy catalyst containing platinum in an amount of 5 to 80 wt% is used as the catalyst.

[0065] According to further preferred embodiments, the catalyst is mixed with the solvent and thoroughly dispersed by ultrasonication and stirring. The polymer electrolyte is preferably added to the mixture and thoroughly dispersed by repeated ultrasonication and stirring. Furthermore, the solvent is suitably removed under reduced pressure to provide a suitable solids content and viscosity, so that the solids content of the catalyst slurry is 5 to 30 wt.% based on the total weight of the catalyst slurry after removal of the solvent, thereby maintaining a suitable viscosity.

[0066] According to further preferred embodiments, the prepared catalyst slurry is suitably milled using a planetary ball mill to reduce the particle size of the catalyst and make it more uniform. Preferably, balls with a diameter of 1 to 10 mm are used in an amount of 50 to 500 parts by weight, based on 100 parts by weight of the catalyst slurry. The milling process is carried out at a rotation speed of 20 to 200 rpm for 0.1 to 5 hours.

[0067] According to preferred embodiments of the present invention, 1 to 60 parts by weight of carbon nanotubes as carbon nanofibers are added to the catalyst slurry, based on 100 parts by weight of the carbon-supported catalyst, wherein the carbon nanotubes are also added in a slurry state.

[0068] To prepare a carbon nanotube slurry, the carbon nanotubes are appropriately mixed with the same solvent used during the preparation of the catalyst slurry, the same amount of the polymer electrolyte is added to the mixture and dispersed by high-energy ultrasonic treatment.

[0069] The solid content of the carbon nanotube slurry prepared in this way is preferably measured by mixing an appropriate amount of the carbon nanotube slurry with the catalyst slurry, and subjecting the mixture to grinding, ultrasonication, and stirring.

[0070] Subsequently, the solvent is suitably removed under reduced pressure so that the solid content of the carbon nanotube slurry is 1 to 20 wt% based on the total weight of the carbon nanotube slurry after removal of the solvent.

[0071] According to preferred embodiments of the present invention, 1 to 20 parts by weight of cerium zirconium oxide is added to the catalyst slurry as a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst in a solid state.

[0072] Preferably, the cerium zirconium oxide is added in a solid state to the catalyst slurry, and the addition method is not particularly limited.

[0073] The carbon nanotube slurry is added according to the catalyst slurry and the cerium zirconium oxide in a solid state is added to the mixture and fully dispersed, thereby preparing the final catalyst slurry.

[0074] In a further preferred embodiment of the present invention, it is preferred that the solid content (which is the sum of catalyst, ionomer, carbon nanofibers and cerium zirconium oxide) of the catalyst slurry prepared in this way is in a range of 5 to 30 wt% in order to obtain a suitable viscosity and to be easily compressed during the formation of the membrane-electrode assembly.

[0075] The final catalyst slurry is further suitably coated on a support paper and dried at a temperature of 30 to 130 °C, and the dried electrode is thermally compressed onto a polymer membrane, thereby forming the membrane-electrode assembly.

[0076] According to further exemplary embodiments, and in more detail, the dried electrode is suitably arranged at both ends of the polymer membrane and then subjected to thermal compression to form the membrane-electrode assembly. The thermal compression is carried out at a temperature of 100 to 180°C and at a pressure of 50 to 300 kgf (1 kgf = 9.81 N) for 0.5 to 30 minutes. After the thermal compression, the backing paper is preferably suitably removed, thus completing the formation of the membrane-electrode assembly.

[0077] The present invention according to exemplary preferred embodiments will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Examples 1 to 3

[0078] In a first exemplary embodiment, in Example 1, a catalyst slurry was prepared by mixing 4 parts by weight of carbon nanotubes as one of the carbon nanofibers, based on 100 parts by weight of the catalyst, with a solvent (6 parts by weight of the carbon nanotubes were used in Example 2, and 8 parts by weight of the carbon nanotubes were used in Example 3) and adding 10 parts by weight of cerium zirconium oxide as a radical inhibitor to the mixture. The prepared catalyst slurry was appropriately coated on a support paper and dried, and the dried electrode was thermally compressed to a polymer membrane to form a membrane-electrode assembly according to each of the examples. Comparison example

[0079] A conventional membrane electrode assembly that did not contain carbon nanofibers or a radical inhibitor was used. Experimental example 1

[0080] In a further exemplary embodiment, the surfaces of the electrodes according to Examples 1 to 3 and the Comparative Example were photographed using an electron microscope to determine whether cracks were present and the results are shown in the Fig. 7 to 12 shown.

[0081] In the case of the process in which a catalyst layer is formed and the catalyst layer is transferred to a polymer membrane, the catalyst layer may crack depending on the thickness of the catalyst layer, the proportion of a binder material, and the type of catalyst. Fig. 7 it can be seen that large cracks were found in the catalyst layer according to the comparative example.

[0082] This means that in the case of the comparative example, the electrode surface had numerous cracks, and the catalyst layer could therefore be removed during electrode transfer. Even in the case where the catalyst layer was transferred to the polymer membrane, cracks could still form in the catalyst layer, and therefore the polymer membrane could be exposed through the cracks, significantly reducing the service life.

[0083] Furthermore, Fig. 8 that the occurrence of cracks in the surface of the electrode according to Example 1, in which 4 parts by weight of carbon nanofibers were added, is suitably reduced, but even a small amount of cracks is present.

[0084] From the Fig. 9 and Fig. 10, it can also be seen that the occurrence of cracks in the catalyst layers according to Example 2, in which 6 and 8 parts by weight of carbon nanofibers were added, was significantly reduced.

[0085] As a result, as shown in the recording of the Fig. 11, in which 6 parts by weight of carbon nanofibers were added, and in the enlarged image of the Fig. 12, it can be seen that the carbon nanofibers around the cracks in the catalyst layer served to bind the catalyst particles in the catalyst layer, thus preventing the occurrence of cracks. Experimental example 2

[0086] In a further exemplary embodiment, the running performances of the fuel cells were measured and compared with respect to the membrane electrode assemblies according to the examples and comparative examples, and the result is shown in the Fig. 13 to 15 shown.

[0087] The lifetime measurement was performed by measuring the initial power output and then measuring the power output again after a specified period of time at open-circuit voltage (OCV), maintaining the unit cell temperature at 85 °C and the flow rate at 1 l / min (cathode: air, anode: hydrogen). Under these conditions, radical generation is accelerated to promote the decomposition of the polymer electrolyte, making it possible to determine the change in the lifetime of the electrodes in a short period of time.

[0088] As in Fig. As shown in Fig. 13, it can be seen that the running performances of the fuel cells containing the electrode to which carbon nanofibers were added according to the examples of the present invention were slightly increased in the high current region compared to that of the comparative example.

[0089] Furthermore, as in Fig. 14, it can be seen that the lifetime of the electrode in which no radical inhibitor was added according to the comparative example, the OCV after 108 hours was reduced by 39% compared to the initial performance.

[0090] As in Fig. 15, it can be further seen that the lifetime of the electrode to which the radical inhibitor was added according to the examples of the present invention was reduced by only 10% even after 108 hours, from which it can be understood that a decrease in lifetime was significantly improved.

[0091] As described above, the present invention provides the following effects.

[0092] According to the present invention, it is possible to appropriately increase the mechanical strength of the catalyst layer and appropriately maintain the thickness of the catalyst layer after long-term operation by adding carbon nanofibers to the catalyst layer of the electrode of the fuel cell.

[0093] Furthermore, it is possible to appropriately minimize a decrease in performance after long-term operation by adding cerium zirconium oxide (CeZrO4) as a radical inhibitor to the catalyst layer of the electrode to prevent a decrease in the chemical resistance of the fuel cell.

Claims

[1] Electrode for a polymer electrolyte membrane fuel cell, wherein the electrode contains: 100 parts by weight of a carbon-supported catalyst; 20 to 80 parts by weight of a hydrogen ion-conducting polymer electrolyte binder material, based on 100 parts by weight of the carbon-supported catalyst; 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of the carbon-supported catalyst; and 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst, wherein the carbon nanofibers are added to a layer of the carbon-supported catalyst, wherein the carbon nanofibers contain at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns and carbon nanorings, which have a diameter of 5 to 100 nm and a length of more than several hundred nanometers. [2] Electrode according to claim 1, wherein the radical inhibitor has a mean particle size of 2 to 60 nm and contains at least one selected from the group consisting of cerium oxide, zirconium oxide, manganese oxide, aluminum oxide, vanadium oxide and mixtures thereof. [3] Electrode according to claim 1, wherein the catalyst is a platinum or platinum alloy catalyst supported by a catalyst support, the catalyst support comprising at least one selected from the group consisting of carbon powder, carbon black, acetylene carbon black, Ketjen carbon black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanohorns, carbon aerogels, carbon cryogels and carbon nanorings. [4] Electrode according to claim 3, wherein the platinum or platinum alloy catalyst contains platinum in an amount of 5 to 80 wt.%. [5] Method for forming a membrane electrode arrangement, the method comprising: Preparing a catalyst slurry to form an electrode for a fuel cell; Addition of 1 to 60 parts by weight of carbon nanofibers, based on 100 parts by weight of a carbon-supported catalyst, to the catalyst slurry, wherein the carbon nanofibers are in a slurry state; Addition of 1 to 20 parts by weight of a radical inhibitor, based on 100 parts by weight of the carbon-supported catalyst, to the catalyst slurry, wherein the radical inhibitor is in a solid state; Drying the final catalyst slurry, which was prepared by adding the carbon nanofibers in a slurry state and the radical inhibitor in a solid state to the catalyst slurry and by stirring the mixture so that an electrode was formed; and Thermal compression of the dried electrode on a polymer membrane, wherein the carbon nanofibers include at least one selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanohorns and carbon nanorings, which have a diameter of 5 to 100 nm and a length of more than several hundred nanometers. [6] Method according to claim 5, wherein the carbon nanofibers are carbon nanotubes added in an amount of 1 to 60 parts by weight, based on 100 parts by weight of the catalyst, and the radical inhibitor is cerzirkonium oxide added in an amount of 1 to 20 parts by weight, based on 100 parts by weight of the catalyst. [7] Method according to claim 5, further comprising grinding the catalyst slurry using a planetary ball mill to reduce the particle size of the catalyst and make it more uniform. [8] The method of claim 5, wherein the final catalyst slurry has a solid content of 5 to 30 wt.%, the solid content being the sum of the catalyst, the carbon nanofibers, the radical inhibitor and the ionomer. [9] Method according to claim 5, wherein the thermal compression is carried out at a temperature of 100 to 180 °C and at a pressure of 50 to 300 kgf (1 kgf = 9.81 N) for 0.5 to 30 minutes.

Images