Catalyst for fuel cell, method for producing same and fuel cell including same

Abstract

The present invention relates to a catalyst for a fuel cell, the catalyst comprising a support having pores, first metal catalyst particles located inside the pores of the support, and second metal catalyst particles located outside the pores of the support, a manufacturing method thereof, and a membrane electrode assembly including the same.

Description

[Technical Field]

[0001] The present invention relates to a catalyst for a fuel cell, which has excellent cell performance and improved durability due to the presence of metal catalyst particles at a specific ratio both inside and outside a porous support, a method for manufacturing the catalyst, and a fuel cell including the catalyst. [Background technology]

[0002] Fuel cells are cells that directly convert chemical energy generated by the oxidation of fuel into electrical energy, and are attracting attention as a next-generation energy source due to their high energy efficiency and environmentally friendly characteristics such as low pollutant emissions.

[0003] A fuel cell generally has a structure in which an anode and a cathode are formed on either side of an electrolyte membrane, and this structure is called a membrane electrode assembly (MEA).

[0004] Fuel cells can be classified into alkaline electrolyte fuel cells, polymer electrolyte membrane fuel cells (PEMFC), etc. depending on the type of electrolyte membrane. Among them, polymer electrolyte fuel cells are gaining attention as portable, vehicle, and home power sources due to their advantages such as a low operating temperature of less than 100°C, fast start-up and response characteristics, and excellent durability.

[0005] A typical example of such a polymer electrolyte fuel cell is a proton exchange membrane fuel cell (PEMFC), which uses hydrogen gas as fuel.

[0006] To summarize the reactions that occur in a polymer electrolyte fuel cell, first, when fuel such as hydrogen gas is supplied to the oxidizing electrode, hydrogen ions (H + ) and electrons (e -) is produced. The hydrogen ions (H + ) is transferred to the reducing electrode through the polymer electrolyte membrane, and the generated electrons (e - ) is transferred to the reducing electrode via an external circuit. Oxygen is supplied to the reducing electrode, and the oxygen converts to hydrogen ions (H + ) and electrons (e - ) and produces water by oxygen reduction reaction.

[0007] Platinum or other noble metals, which have high catalytic activity and high corrosion resistance, are used as metal catalysts for forming electrodes of membrane electrode assemblies (MEAs).

[0008] Platinum and other precious metals used as catalysts for fuel cells are expensive, which increases the manufacturing costs of fuel cells. Therefore, research is ongoing into technologies that can reduce the amount of metal catalyst used while maintaining cell performance and thereby reduce the manufacturing costs of fuel cells.

[0009] As a technology to increase the active surface area of ​​a catalyst and reduce the amount of catalyst used, a catalyst formed by dispersing metal catalyst particles on the surface of an electrically conductive support (e.g., carbon, metal oxide, C3N4, etc.) has been developed.

[0010] Korean Patent Publication No. 2021-0006991 relates to an electrode catalyst for a fuel cell, and discloses an electrode catalyst consisting of a core portion and a shell portion, in which different metal catalyst particles are supported inside and outside a porous support.

[0011] The patent discloses an electrode catalyst in which 80% or more of metal catalyst particles are supported inside the mesopores of a support with improved catalytic activity, but does not disclose a fuel cell catalyst that has the effect of improving durability without reducing fuel cell performance by optimizing the ratio and size of the internal and external metal catalyst particles depending on the type of support.

[0012] In particular, when a fuel cell is operated for a long period of time, migration and / or oxidation of the metal catalyst from the nanoparticles occurs due to high voltage and a highly acidic environment, accelerating catalyst degradation. Therefore, preventing catalyst degradation due to long-term operation of the fuel cell is very important for improving the durability and lifespan of the fuel cell.

[0013] Therefore, in order to improve the performance and service life of fuel cells, research into fuel cell catalysts with excellent performance and durability is ongoing.

[0014] [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Republic of Korea Patent Publication No. 2021-0006991 (2021.01.19) Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention aims to provide a catalyst for a fuel cell that has excellent performance and durability by adjusting the content of metal catalyst particles supported inside the pores of the support and metal catalyst particles supported outside the support.

[0017] Another object of the present invention is to provide a method for producing a fuel cell catalyst that contains metal catalyst particles inside and outside the pores of the carrier.

[0018] According to the present invention, it is possible to provide a fuel cell having an improved lifespan without any deterioration in fuel cell performance compared to existing fuel cell catalysts. [Means for solving the problem]

[0019] According to one aspect of the present invention, there is provided a catalyst for a fuel cell, comprising: a support having pores; first metal catalyst particles located inside the pores of the support; and second metal catalyst particles located outside the pores of the support.

[0020] The fuel cell catalyst has a ratio (M1 / M2) of the number of the first metal catalyst particles (M1) to the number of the second metal catalyst particles (M2) of 300 m 2 / g or more, the ratio is 0.25 to 0.67, and the specific surface area of ​​the carrier is 300 m 2 If it is less than 1 / g, the ratio can be 0.05 to 0.25.

[0021] The first metal catalyst particles and the second metal catalyst particles may have a diameter ratio of 1:1 to 3.

[0022] The first metal catalyst particles and the second metal catalyst particles may each independently have an average diameter of 2 to 17 nm.

[0023] The size of the carrier may be 15 to 60 nm.

[0024] The carrier pore size may be 2 to 15 nm.

[0025] The first metal catalyst particles and the second metal catalyst particles are each independently selected from the group consisting of Pt, Pt—Pd, Pt—Mn, Pt—Sn, Pt—Mo, Pt—Cr, Pt—W, Pt—Ru, Pt—Ni, Pt—Co, Pt—Y, Pt—Ru—W, Pt—Ru—Ir, Pt—Ru—Ni, Pt—Ru—Mo, Pt—Ru—Rh—Ni, Pt—Ru—Sn—W, Pt—Ru—Ir—Ni, It can be selected from the group consisting of Pt—Ru—Ir—Y, Pt—Co—Mn, Pt—Co—Ni, Pt—Co—Fe, Pt—Co—Ir, Pt—Co—S, Pt—Co—P, Pt—Fe, Pt—Fe—Ir, Pt—Fe—S, Pt—Fe—P, Pt—Au—Co, Pt—Au—Fe, Pt—Au—Ni, Pt—Ni—Ir, Pt—Cr and Pt—Cr—Ir.

[0026] According to another aspect of the present invention, there is provided a method for manufacturing the above-mentioned fuel cell catalyst, including: a) forming metal catalyst particle seeds from a metal catalyst precursor solution; b) adding a carrier to the solution and then allowing the metal catalyst particle seeds to penetrate pores in the carrier and adsorb onto the surface of the carrier; and c) reducing and growing the metal catalyst particles of step b).

[0027] The step a) may involve preparing seeds in the form of partially reduced or hydrated metal ligands from a metal catalyst precursor solution.

[0028] Step a) may be performed by mixing at least one additive selected from the group consisting of formaldehyde, formic acid, citric acid, ascorbic acid, urea, and hexamethylenetetramine with a metal catalyst precursor to prepare a metal catalyst precursor solution, and then heating the solution.

[0029] The step b) may be performed using vacuum infiltration.

[0030] In step b), the metal catalyst precursor solution may contain an alcohol solvent, and the support may be pretreated to make the inside of the pores hydrophilic before step b).

[0031] The step c) is carried out by adding a reducing agent, and the reducing agent may include one or more selected from the group consisting of formaldehyde, formic acid, ascorbic acid, hexamethylenetetramine, citric acid, and ethylene glycol.

[0032] According to another aspect of the present invention, there is provided a membrane electrode assembly including the fuel cell catalyst described above.

[0033] According to another aspect of the present invention, there is provided a fuel cell including the membrane electrode assembly described above. [Effects of the Invention]

[0034] The fuel cell catalyst according to the present invention has the effect of improving durability without deteriorating cell performance by forming metal catalyst particle seeds and then adjusting the metal catalyst loading ratio and particle size inside / outside the pores of the carrier using a physical method such as vacuum impregnation.

[0035] The catalyst for a fuel cell according to the present invention has improved performance and durability, thereby reducing the manufacturing costs of a fuel cell including the catalyst. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a reconstructed image of STEM and TEM images of an electrode catalyst for a fuel cell according to an embodiment of the present invention.

[0037] [Figure 2] 10 is a reconstructed STEM image (3D tomography) of an electrode catalyst for a fuel cell according to another embodiment of the present invention.

[0038] [Figure 3] 1 is a cross-sectional view schematically illustrating a membrane electrode assembly according to the present invention.

[0039] [Figure 4] 1 is a schematic diagram showing the overall configuration of a fuel cell according to an embodiment of the present invention;

[0040] [Figure 5] 5(a) and 5(b) show the particle size distribution of metal catalyst particles inside and outside pores manufactured according to Comparative Example 2 (FIG. 5(a)) and Example (FIG. 5(b)).

[0041] [Figure 6] 1 shows the performance evaluation results of catalysts prepared using carriers with a specific surface area of ​​300 m 2 / g or more according to examples and comparative examples of the present invention.

[0042] [Figure 7]1 shows the performance evaluation results of catalysts prepared using carriers with a specific surface area of ​​less than 300 m 2 / g according to examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, each configuration of the present invention will be described in more detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited to the following content.

[0044] The terms "preferred" or "preferably" used herein refer to embodiments of the invention that have certain advantages under certain conditions. However, other embodiments may also be preferred under the same or different conditions. Furthermore, the presence of one or more preferred embodiments does not imply that other embodiments are not useful, nor does it exclude other embodiments within the scope of the invention.

[0045] As used herein, the term "comprising" is used to list materials, compositions, devices, and methods useful in the present invention, but is not limited to the listed examples.

[0046]

[0047] The present invention relates to a catalyst for a fuel cell, comprising a support having pores, first metal catalyst particles located inside the pores of the support, and second metal catalyst particles located outside the pores of the support.

[0048] The support may be any support that can be used in the technical field of catalysts for fuel cells, and may be, for example, a carbon-based support, a porous inorganic oxide support such as zirconia, alumina, titania, silica, or ceria, or a zeolite support.

[0049] Preferably, a carbon-based support having excellent electrical conductivity may be used, and the carbon-based support may be selected from the group consisting of graphite, super P, carbon fiber, carbon sheet, carbon black, Ketjen Black, Denka Black, acetylene black, carbon nanotube (CNT), carbon sphere, carbon ribbon, fullerene, activated carbon, carbon nanofiber, carbon nanowire, carbon nanoball, carbon nanohorn, carbon nanocage, carbon nanoring, ordered nano- / meso-porous carbon, carbon aerogel, mesoporous carbon, graphene, stabilized carbon, activated carbon, and a combination of two or more thereof.

[0050] Specifically, the ratio (M1 / M2) of the number of the first metal catalyst particles (M1) to the number of the second metal catalyst particles (M2) is determined so that the content of the first catalyst particles supported inside the pores of the support varies depending on the specific surface area of ​​the support. 2 When using a carrier with a specific surface area of ​​300 m / g or more, the specific surface area is 0.25 to 0.67. 2 When using a carrier with less than 1 / g, the ratio is adjusted to 0.05 to 0.25. Metal catalyst particles are supported on both the inside and outside of the carrier, and by limiting the ratio, it is possible to improve the performance of the fuel cell and the durability of the catalyst, thereby improving the lifespan of the cell.

[0051] In the present invention, the content of the first catalyst particles loaded inside the pores is varied depending on the specific surface area of ​​the support in order to maximize the activity and durability of the metal catalyst particles depending on the shape of the support. 2When the specific surface area of ​​the carrier is 300 m / g or more, if the content is less than the above content, durability may decrease, and if the content is more than the above content, performance may decrease. 2 When the content is less than the above range, durability may be reduced if the content is less than the above range, and performance may be reduced if the content is more than the above range.

[0052]

[0053] In addition, in the catalyst for a fuel cell according to the present invention, the first metal catalyst particles and the second metal catalyst particles may have an average diameter ratio of 1:1 to 3.

[0054] Preferably, the ratio may be 1:1.1 to 2.5, and more preferably, the ratio may be 1:1.2 to 2.

[0055] If the average diameter of the second metal catalyst particles is larger than the above ratio, there may be a problem of reduced fuel cell performance.

[0056] In this case, the first metal catalyst particles and the second metal catalyst particles may each have a diameter of 2 to 17 nm (nanometers) independently, and taking into account the ratio of the average diameters, the size of the second metal catalyst particles is larger than the size of the first metal catalyst particles.

[0057] In particular, in the catalyst for a fuel cell according to the present invention, the support may have a size (diameter) of 15 to 60 nm (nanometers) and a pore size of 2 to 15 nm (nanometers).

[0058] The size (diameter) of the carrier pores may preferably be 2 to 13 nm, most preferably 2 to 10 nm.

[0059] If the pores are smaller than this size, there may be a problem that there are no metal catalyst particles located inside the pores, and if the pores are larger than this size, there may be a problem that the ratio of metal catalyst particles inside and outside the pores is difficult.

[0060] Meanwhile, since the first metal catalyst particles are supported inside the pores of the carrier, it is preferable that the ratio of the size of the first metal catalyst particles to the diameter of the pores of the carrier is 0.8 to 1.1.

[0061] The present invention is characterized by improving durability without reducing catalyst performance by specifying the content ratio according to the size and position of metal catalyst particles supported on a carrier used in existing fuel cell catalysts.

[0062] Since the components of the catalyst are not significantly different from those of existing fuel cell catalysts, the size and content ratio of the metal catalyst particles and the positions of the pores (inside and outside) can be specified to improve performance and durability, and the manufacturing cost is not significantly different and the catalyst can be manufactured using existing manufacturing equipment. The first metal catalyst particle and the second metal catalyst particle may each be platinum or a platinum-based alloy, and specifically, may be Pt-Pd, Pt-Mn, Pt-Sn, Pt-Mo, Pt-Cr, Pt-W, Pt-Ru, Pt-Ni, Pt-Co, Pt-Y, Pt-Ru-W, Pt-Ru-Ir, Pt-Ru-Ni, Pt-Ru-Mo, Pt-Ru-Rh-Ni, Pt-Ru-Sn-W, Pt t-Ru-Ir-Ni, Pt-Ru-Ir-Y, Pt-Co-Mn, Pt-Co-Ni, Pt-Co-Fe, Pt-Co-Ir, Pt-Co-S, Pt-Co-P, Pt-Fe, Pt-Fe -Ir, Pt-Fe-S, Pt-Fe-P, Pt-Au-Co, Pt-Au-Fe, Pt-Au-Ni, Pt-Ni, Pt-Ni-Ir, Pt-Cr or Pt-Cr-Ir.

[0063] The first metal catalyst particles and the second metal catalyst particles do not necessarily have to be the same, and may be different, and may be composed of a single type of catalyst, or may each be composed of multiple types of metal catalyst particles.

[0064]

[0065] Meanwhile, the fuel cell catalyst according to the present invention is produced by the following method.

[0066] The fuel cell catalyst according to the present invention, in which first and second metal catalyst particles are supported inside and outside the pores of the support, can be manufactured by sequentially carrying out the following steps: a) forming metal catalyst particle seeds from a metal catalyst precursor solution; b) adding a support to the solution and then allowing the metal catalyst particle seeds to penetrate into the pores in the support and adsorb onto the surface of the support; and c) reducing and growing the metal catalyst particle seeds of step b).

[0067] Specifically, step a) involves forming metal catalyst particle seeds by partially reducing or hydrated metal ligand-form seeds from a metal catalyst precursor in a metal catalyst precursor solution under mild conditions. Additives used to form the seeds include weak reducing agents such as formaldehyde, formic acid, citric acid, and ascorbic acid in a diluted state, and urea and hexamethylenetetramine. More specifically, step a) is performed by mixing at least one additive selected from the group consisting of formaldehyde, formic acid, citric acid, ascorbic acid, urea, and hexamethylenetetramine with the metal catalyst precursor to prepare a metal catalyst precursor solution and then heating the mixture.

[0068] In particular, when urea or hexamethylenetetramine is used, the heating may be carried out at a temperature of 80 to 110° C. for 0.5 to 3 hours.

[0069] If the reaction is carried out at a temperature lower than the above temperature, there is a problem that metal catalyst particle seeds are not formed, and if the reaction is carried out at a temperature higher than the above temperature, there is a problem that the metal catalyst particle seeds are reduced, resulting in the metal catalyst particles becoming larger.

[0070] If the reaction time is shorter than the above range, metal catalyst particle seeds may not be formed, and if the reaction time is longer than the above range, the metal catalyst particle seeds may be reduced, resulting in larger metal catalyst particles.

[0071] Specifically, step b) may be performed by (i) vacuum infiltration, (ii) using a solvent with good wettability, or (iii) by separately pretreating the pores of the carrier to make them hydrophilic before step b).

[0072] In particular, step b) is a process for facilitating the infiltration of the metal catalyst particle seeds into the pores of the support. After the metal catalyst particle seeds are infiltrated into the mesopores (excluding micropores of 2 nm or less) using a vacuum infiltration method, an additional reduction reaction can be induced in the subsequent step c) to form first and second metal catalyst particles.

[0073] Specifically, when the vacuum infiltration method is used, it can be carried out under a pressure of 0.01 to 90 kPa for 5 to 30 minutes.

[0074] If the pressure is lower than the above range, the metal catalyst particles located inside the pores of the carrier may increase, resulting in a decrease in performance. If the pressure is higher than the above range, the metal catalyst particles located inside the pores of the carrier may decrease.

[0075] If the time is shorter than the above, there is a problem that the effect of infiltrating the metal catalyst particle seeds into the pores using the actual vacuum infiltration method is negligible, and if the time is longer than the above, there is a problem that the metal catalyst particles located inside the pores of the carrier increase, resulting in a decrease in performance.

[0076] Alternatively, in step (b), instead of (i) using a vacuum infiltration method, (ii) a solvent with good wettability may be used, or (iii) the pore surface of the support may be separately modified to be hydrophilic, thereby improving the infiltration ability of the metal catalyst precursor solution.

[0077] The metal catalyst precursor solution may contain a hydrophilic solvent, such as an alcohol-based solvent, which improves the penetration of the solution and facilitates the production of first metal catalyst particles by penetration of metal catalyst particle seeds. The alcohol solvent may be an alcohol having 1 to 6 carbon atoms. Specifically, the alcohol may contain one or more alcohols, including chain alcohols and branched alcohols having 2 to 4 carbon atoms. The hydrophilic solvent of the metal catalyst precursor solution may include, for example, one or more selected from the group consisting of isopropyl alcohol, ethanol, butyl alcohol, n-propyl alcohol, acetone, and formic acid.

[0078] The hydrophilic modification of the inner pore surfaces of the carrier can be performed by a variety of methods, without particular limitation, as long as the method can impart hydrophilicity to the surface. For example, methods such as surface plasma treatment and hydrophilic functional group modification can be used. Specifically, a method of surface modification with hydrophilic functional groups can be used. In this case, the carrier can be immersed in a reactive solution for hydrophilic modification, which has the advantage that the surface deep inside the pores can be modified.

[0079] The hydrophilic functional group is not particularly limited and may be any functional group that has hydrophilic properties, such as a hydroxy group, a carboxylic acid group, an amine group, or a sulfonic acid group.

[0080] The hydrophilic functional group may be modified with one type of hydrophilic functional group, or may be modified with different types of hydrophilic functional groups.

[0081] In this way, the support whose pore inner surface has been modified with hydrophilic functional groups is immersed in a metal catalyst precursor solution containing an alcohol-based solvent, and a reduction reaction is carried out under conditions in which the penetration rate of the solution into the support pores is improved, thereby allowing first metal catalyst particles to be formed inside the pores.

[0082] The reduction step in step c) is carried out by adding a reducing agent in step c) after the metal catalyst particle seeds have penetrated into the pores of the support in step b).

[0083] The reducing agent may include one or more selected from the group consisting of weak reducing agents used in forming the metal catalyst particle seeds, such as formaldehyde, formic acid, citric acid, ascorbic acid, hexamethylenetetramine, and ethylene glycol, and preferably includes hexamethylenetetramine or ethylene glycol.

[0084] The reducing agent may be added in an equivalent ratio of 10 to 200 per mole of the metal catalyst precursor.

[0085] If the metal catalyst precursor is added at a ratio lower than the above-mentioned equivalent ratio, the metal catalyst precursor is not sufficiently reduced, resulting in a low content of metal catalyst particles and a decrease in performance and durability. If the metal catalyst precursor is added at a ratio higher than the above-mentioned equivalent ratio, there is a problem that the physical properties of the catalyst produced do not differ significantly compared to the amount added. Therefore, from the perspective of production efficiency, it is preferable to add the metal catalyst precursor at a ratio equal to or lower than the above-mentioned equivalent ratio.

[0086] The metal catalyst precursor of the fuel cell catalyst according to the present invention is not particularly limited as long as it can be formed into the first metal catalyst particles and the second metal catalyst particles by a reduction reaction, and any metal catalyst precursor commonly used in the technical field of fuel cell catalysts can be used. For example, it may be a salt of platinum or a platinum-based alloy, which can be the first metal catalyst particles and the second metal catalyst particles.

[0087] The catalyst for a fuel cell of the present invention can be prepared by mixing an ionomer and a dispersion medium used in an ion conductor dispersion to prepare a catalyst slurry, and the prepared catalyst slurry can be used to form an anode and / or cathode of a membrane electrode assembly.

[0088] The membrane electrode assembly of the present invention is manufactured by forming a catalyst layer on the surface of a release film using the catalyst slurry, and then transferring the catalyst layer onto the polymer electrolyte membrane by applying heat and pressure while the catalyst layer is in contact with the polymer electrolyte membrane, or by directly coating the catalyst slurry onto the polymer electrolyte membrane to form an electrode.

[0089] The membrane electrode assembly includes an oxidizing electrode, a reducing electrode, and a polymer electrolyte membrane therebetween, and at least one of the oxidizing electrode and the reducing electrode contains the fuel cell catalyst of the present invention.

[0090] The ionomer, which is mixed with the fuel cell catalyst to form the catalyst slurry, is used for hydrogen ion transport and also functions as a binder to improve adhesion between the electrode and the polymer electrolyte membrane. The ionomer may be a cation conductor having at least one proton exchange group selected from the group consisting of a sulfonic acid group, a carboxyl group, a boronic acid group, a phosphate group, an imide group, a sulfonimide group, a sulfonamide group, a sulfonyl fluoride group, and combinations thereof.

[0091] Specifically, the ionomer according to one embodiment of the present invention may be a fluorine-based cation conductor having sulfonic acid groups and / or carboxyl groups, a hydrocarbon-based cation conductor having sulfonic acid groups and / or carboxyl groups, or a mixture thereof.

[0092] It is preferable to adjust the catalyst content in the catalyst slurry so that the weight of the catalyst is 20 to 80 wt % of the total weight of the electrode. If the catalyst content in the electrode is less than 20 wt %, the required catalytic activity of the electrode may not be satisfied. On the other hand, if the catalyst content in the electrode is more than 80 wt %, the catalyst may aggregate, reducing the active area of ​​the catalyst and decreasing the catalytic activity.

[0093]

[0094] The invention will now be explained in more detail with reference to the drawings.

[0095] However, this is merely an example for understanding the present invention, and does not limit the scope of the present invention.

[0096]

[0097] 1 shows edited STEM images of a fuel cell electrode catalyst according to one embodiment of the present invention, and edited TEM images of a fuel cell electrode catalyst according to another embodiment of the present invention. The STEM image highlights the second metal catalyst particles, while the TEM image distinguishes the first metal catalyst particles from the second metal catalyst particles.

[0098] Referring to FIG. 1, metal catalyst particles are present inside and outside the support, and as described above, the first metal catalyst particles located inside the pores of the support and the second metal catalyst particles located outside the pores satisfy the content ratio and size ratio, thereby achieving improved performance and durability.

[0099] In particular, Figure 1 shows the specific surface area of ​​the support is 300m 2 / g or more, and the specific surface area of ​​the carrier is 300m 2 / g.

[0100] By adjusting the catalyst content according to the range of the specific surface area of ​​the support, the performance and durability can be enhanced.

[0101] 3 is a cross-sectional view schematically illustrating a membrane electrode assembly according to the present invention. Referring to FIG. 3, the membrane electrode assembly 100 includes the polymer electrolyte membrane 50 and electrodes 20, 20' disposed on both sides of the polymer electrolyte membrane 50. The electrodes 20, 20' include electrode substrates 40, 40' and catalyst layers 30, 30' formed on the surfaces of the electrode substrates 40, 40'. A microporous layer (not shown) containing conductive fine particles such as carbon powder or carbon black may be further included between the electrode substrates 40, 40' and the catalyst layers 30, 30' to facilitate material diffusion within the electrode substrates 40, 40'.

[0102] In the membrane electrode assembly 100, the electrode 20 disposed on one side of the ion exchange membrane 50 and performing an oxidation reaction to generate hydrogen ions and electrons from the fuel delivered to the catalyst layer 30 through the electrode substrate 40 is called the anode electrode, and the electrode 20' disposed on the other side of the ion exchange membrane 50 and performing a reduction reaction to generate water from the hydrogen ions supplied through the ion exchange membrane 50 and the oxidant delivered to the catalyst layer 30' through the electrode substrate 40' is called the cathode electrode.

[0103] The electrode substrates 40, 40' may be porous conductive substrates to facilitate the supply of hydrogen or oxygen. Representative examples include, but are not limited to, carbon paper, carbon cloth, carbon felt, or metal cloth (a porous film made of fibrous metal cloth or a metal film formed on the surface of a cloth made of polymeric fiber). Furthermore, it is preferable to use electrode substrates 40, 40' that are water-repellent treated with fluorine-based resin, since this prevents a decrease in reactant diffusion efficiency due to water generated during fuel cell operation.

[0104] The fluorine-based resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, fluorinated ethylene propylene, polychlorotrifluoroethylene, or a copolymer thereof.

[0105]

[0106] A fuel cell according to an embodiment of the present invention includes the membrane electrode assembly, and may be, for example, a fuel cell that uses hydrogen gas as fuel.

[0107] FIG. 4 is a schematic diagram showing the overall configuration of a fuel cell according to an embodiment of the present invention.

[0108] Referring to FIG. 4, the fuel cell 200 includes a fuel supply unit 210 that supplies a mixed fuel obtained by mixing fuel and water, a reforming unit 220 that reforms the mixed fuel to generate a reformed gas containing hydrogen gas, a stack 230 that generates electrical energy by electrochemically reacting the reformed gas containing hydrogen gas supplied from the reforming unit 220 with an oxidant, and an oxidant supply unit 240 that supplies an oxidant to the reforming unit 220 and the stack 230.

[0109] The stack 230 includes a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between the reformed gas, including hydrogen gas, supplied from the reforming unit 220 and an oxidant supplied from the oxidant supplying unit 240.

[0110] Each unit cell refers to a unit cell that generates electricity and includes a membrane electrode assembly that oxidizes / reduces oxygen in a reformed gas containing hydrogen gas and an oxidant, and a separator plate (also called a bipolar plate, hereinafter referred to as "separator plate") that supplies the reformed gas containing hydrogen gas and the oxidant to the membrane electrode assembly. The separator plates are located on both sides of the membrane electrode assembly, with the membrane electrode assembly at the center. In this case, the separator plates located at the outermost sides of the stack are sometimes referred to as end plates.

[0111] Of the separation plates, the end plate includes a first pipe-shaped supply pipe 231 for injecting the reformed gas containing hydrogen gas supplied from the reforming section 220, and a second pipe-shaped supply pipe 232 for injecting oxygen gas, and the other end plate includes a first exhaust pipe 233 for discharging the reformed gas containing hydrogen gas that ultimately remains unreacted in the multiple unit cells to the outside, and a second exhaust pipe 234 for discharging the oxidant that ultimately remains unreacted in the unit cells to the outside.

[0112] The present invention will be described in more detail below based on examples, but this is merely an illustrative description for understanding the present invention, and the scope of the present invention is not limited to the following examples.

[0113]

[0114] [Example 1]

[0115] 1g of H2PtCl6 is added to a solution of 1g of urea dissolved in water, and heated under reflux at 100°C for 2 hours to form Pt catalyst particle seeds.

[0116] The solution was added to Vulcan (surface area 320 m 2 Add 0.47g of carbon (0.1g / g) and disperse evenly.

[0117] The solution was placed in a simple vacuum adsorption device and subjected to a vacuum of 10 kPa for 20 minutes to adsorb the Pt catalyst particle seeds into the pores of the carbon support.

[0118] A reducing agent such as ethylene glycol or hexamethylenetetramine is added to the vacuum adsorption treated solution in an equivalent ratio of 50 to perform additional reduction, followed by filtering and drying to prepare a catalyst.

[0119]

[0120] [Example 2]

[0121] The surface area of ​​320 m used in Example 1 2 / g of Vulcan carbon instead of a surface area of ​​120m 2 The process was the same except that 1 / g of Acetylene black was used.

[0122]

[0123] [Comparative Example 1]

[0124] The catalyst was prepared by dispersing catalyst particles H2PtCl6 and Vulcan carbon support in a solvent and reducing them with NaBH4 in the usual catalyst preparation method.

[0125]

[0126] Comparative Example 2

[0127] The Vulcan carbon support was pretreated with distilled water according to the pretreatment method, and then the catalyst precursor H2PtCl6 was added. After additional vacuum treatment (10 kPa, 60 minutes), reduction was performed to prepare the catalyst.

[0128]

[0129] Comparative Example 3

[0130] In a conventional catalyst manufacturing method, instead of Vulcan carbon of Comparative Example 1, a catalyst with a surface area of ​​120 m 2 The catalyst was prepared in the same manner as in Comparative Example 1, except that 1 / g of Acetylene Black was used.

[0131]

[0132] [Manufacturing example]

[0133] The membrane electrode assemblies were fabricated in the same manner except that the catalysts prepared in the examples and comparative examples were used.

[0134]

[0135] [Evaluation Example 1] Particle size and distribution measurement by STEM and TEM analysis

[0136] STEM and TEM analyses were performed to examine the particle size and size distribution of the catalysts prepared in Comparative Example 2 and Example 1, and the results are shown in Figures 5(a) and 5(b), respectively. Figures 5(a) and 5(b) show that the catalyst of the comparative example has no difference in the size of catalyst particles distributed inside and outside the pores (Figure 5(a)), whereas the catalyst prepared by the preparation method of the present invention has catalyst particles of different sizes distributed inside and outside the pores (Figure 5(b)).

[0137]

[0138] Furthermore, the number ratio, average size, etc. of the catalysts prepared in Comparative Example 2, Example 1, and Comparative Examples 1 and 3 were measured and are shown in Tables 1 and 2 below.

[0139] [Table 1]

[0140]

[0141] [Table 2]

[0142] It can be seen from Tables 1 and 2 that the catalysts of Examples 1 and 2 according to the present invention satisfy the M1 / M2 ratio range of the present invention.

[0143]

[0144] [Evaluation Example 2] Battery performance evaluation: 80℃, 50RH conditions evaluation results

[0145] The catalysts of the comparative examples and examples shown in Table 1 (non-surface area 300 m 2 Fuel cells were fabricated using catalysts (prepared using a carrier with a surface area of ​​300 m or more) and the cell performance was evaluated. The results are shown in Figure 6. In addition, the catalysts of the comparative example and the example shown in Table 2 (prepared using a carrier with a surface area of ​​300 m or more) were fabricated using catalysts (prepared using a carrier with a surface area of ​​300 m or more). 2 A fuel cell was fabricated using the catalyst (prepared using a carrier with less than 10 ...

[0146]

[0147] [Evaluation Example 3] Catalyst durability evaluation The catalysts of Comparative Example 1, Comparative Example 2 and Example 1 (non-surface area 300 m 2 / g or more), and the catalysts of Comparative Example 3 and Example 2 (non-surface area 300 m 2 DOE catalyst durability evaluation experiments were carried out on catalysts (prepared using supports with less than 1000 kJ / g), and the results are shown in Table 3.

[0148]

[0149] [Table 3]

[0150] From Table 3, it can be seen that the catalysts of Comparative Examples 1 and 3 prepared by conventional methods showed a larger voltage loss after 10,000 cycles of DOE than the catalysts of the Examples according to the present invention.

[0151] On the other hand, Comparative Example 2 is a catalyst in which 80% or more of the metal catalyst particles are supported within the pores, and it has been confirmed that performance is reduced from the aforementioned Evaluation Example 2. In contrast, although the catalyst of the Example has been optimized to increase activity, as shown in Table 3, the voltage decrease is similar to that of Comparative Example 2. This means that the catalyst of the Example exhibits higher performance and catalytic durability equivalent to or greater than that of the catalyst of Comparative Example 2.

Claims

1. A support having pores; first metal catalyst particles located within the pores of the support; and second metal catalyst particles located outside the pores of the support; Including, the first metal catalyst particles and the second metal catalyst particles are comprised in a diameter ratio of 1:1.1 to 2.5; The ratio (M1 / M2) of the number of the first metal catalyst particles (M1) to the number of the second metal catalyst particles (M2) is When the specific surface area of ​​the carrier is 300 m 2 / g or more, the ratio is 0.25 to 0.67; When the specific surface area of ​​the support is less than 300 m 2 / g, the ratio is 0.05 to 0.25; Catalyst for fuel cells.

2. 2. The catalyst for a fuel cell according to claim 1, wherein the first metal catalyst particles and the second metal catalyst particles each have an average diameter of 2 to 17 nm.

3. 2. The catalyst for a fuel cell according to claim 1, wherein the size of the support is 15 to 60 nm.

4. 2. The catalyst for a fuel cell according to claim 1, wherein the size of the pores of the support is 2 to 15 nm.

5. The first metal catalyst particles and the second metal catalyst particles are each independently selected from Pt, Pt—Pd, Pt—Mn, Pt—Sn, Pt—Mo, Pt—Cr, Pt—W, Pt—Ru, Pt—Ni, Pt—Co, Pt—Y, Pt—Ru—W, Pt—Ru—Ir, Pt—Ru—Ni, Pt—Ru—Mo, Pt—Ru—Rh—Ni, Pt—Ru—Sn—W, Pt—Ru—Ir—Ni, Pt—Ru—Ir—Y, 2. The fuel cell catalyst according to claim 1, which is one or more selected from the group consisting of Pt—Co—Mn, Pt—Co—Ni, Pt—Co—Fe, Pt—Co—Ir, Pt—Co—S, Pt—Co—P, Pt—Fe, Pt—Fe—Ir, Pt—Fe—S, Pt—Fe—P, Pt—Au—Co, Pt—Au—Fe, Pt—Au—Ni, Pt—Ni—Ir, Pt—Cr, and Pt—Cr—Ir.

6. A method for producing a fuel cell catalyst according to claim 1, comprising: a) forming metal catalyst particle seeds from a metal catalyst precursor solution; b) adding a support to the solution, and then allowing the metal catalyst particle seeds to penetrate into the pores in the support and adsorb onto the surface of the support; c) reducing and growing the metal catalyst particle seeds of step b); After reduction, the first metal catalyst particles formed inside the pores of the support and the second metal catalyst particles formed outside the pores and adsorbed on the surface of the support have a diameter ratio of 1:1.1 to 2.5; The ratio (M1 / M2) of the number of the first metal catalyst particles (M1) to the number of the second metal catalyst particles (M2) is When the specific surface area of ​​the carrier is 300 m 2 / g or more, the ratio is 0.25 to 0.67; When the specific surface area of ​​the support is less than 300 m 2 / g, the ratio is 0.05 to 0.25; A method for producing a fuel cell catalyst.

7. 7. The method for preparing a fuel cell catalyst according to claim 6, wherein step a) comprises preparing seeds in the form of partially reduced or hydrated metal ligands from a metal catalyst precursor solution.

8. 7. The method of claim 6, wherein step a) is performed by mixing at least one additive selected from the group consisting of formaldehyde, formic acid, citric acid, ascorbic acid, urea, and hexamethylenetetramine with a metal catalyst precursor to prepare a metal catalyst precursor solution, and then heating the metal catalyst precursor solution.

9. 7. The method of claim 6, wherein step b) is performed using vacuum infiltration.

10. In step b), the metal catalyst precursor solution contains an alcohol solvent; 7. The method of claim 6, wherein the support is pretreated to make the inside of the pores hydrophilic before the step b).

11. The step c) is carried out by adding a reducing agent; 7. The method for producing a catalyst for a fuel cell according to claim 6, wherein the reducing agent comprises at least one selected from the group consisting of formaldehyde, formic acid, ascorbic acid, hexamethylenetetramine, citric acid, and ethylene glycol.

12. A membrane electrode assembly comprising the fuel cell catalyst according to claim 1.

13. A fuel cell comprising a membrane electrode assembly according to claim 12.

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