Gas diffusion layer comprising microporous layer containing radical scavenger including cerium oxide particles having controlled shape, and fuel cell employing same

Abstract

Provided is a gas diffusion layer for a fuel cell. The gas diffusion layer comprises a carbon substrate and a microporous layer formed on the carbon substrate. The microporous layer contains carbon particles and a water-repellent resin that binds the carbon particles. The microporous layer contains a radical scavenger including nano-sized cerium oxide particles that have a controlled particle shape, which is rectangular parallelepiped, a cube, an octahedron, or a polyhedron having nine or more surfaces, and are doped with at least one non-metallic element selected from among nitrogen, phosphorus, sulfur, chlorine, and fluorine and / or at least one metal element selected from among La, Pr, Sm, Eu, Gd, Y, Zr, and Nb. The gas diffusion layer can effectively improve the durability of a fuel cell manufactured using same.

Description

A gas diffusion layer comprising a microporous layer containing a radical trapping agent including cerium oxide particles having a controlled shape, and a fuel cell employing the same

[0001] This patent application is about the research results conducted by the main organization, JNT Co., Ltd., and the Seoul Metropolitan University Industry-Academic Cooperation Foundation, a joint research institute, under the project of Development of a 25kW-class PEMFC stack for hydrogen fuel cell power generation with an electrical efficiency of 66.7%, a current density of 220mA / cm2@0.8V, and a lifespan of 3uV / h-cell, under the implementing agency: Ministry of Trade, Industry and Energy of the Republic of Korea, Project number: 20203010030010, Research management specialized organization: Korea Institute of Energy Technology Evaluation and Planning, Project name: Industrial Technology Innovation Project, Project name: Development of a 25kW-class PEMFC stack for hydrogen fuel cell power generation with an electrical efficiency of 66.7%, a current density of 220mA / cm2@0.8V, and a lifespan of 3uV / h-cell.

[0002] This patent application also relates to the results of research conducted by JNTG Co., Ltd., the lead organization, and the Seoul Metropolitan University Industry-Academic Cooperation Foundation, a joint research organization, under the project titled “Development of Post-processing and Mass Production Technology of Conductive Carbon Black for Fuel Cell Gas Diffusion Layers,” which is administered by the Ministry of Trade, Industry and Energy of the Republic of Korea, Project No.: P0017349, Research Management Specialist Organization: Korea Institute for Advancement of Technology, Project Name: Development of Core Technologies for New Industry Entry Business Restructuring, Project Name: Development of Post-processing and Mass Production Technology of Conductive Carbon Black for Fuel Cell Gas Diffusion Layers.

[0003] The present disclosure relates to a gas diffusion layer comprising a microporous layer including a radical trapping agent comprising cerium oxide particles, and a fuel cell employing the same. More specifically, the present disclosure relates to a gas diffusion layer comprising a microporous layer including a radical trapping agent comprising cerium oxide particles having a controlled shape, and a fuel cell employing the same.

[0004] Fuel cells are devices that generate electrical energy through an electrochemical reaction between fuel and oxygen. Because they are not heat engines, they possess high efficiencies exceeding the Carnot limit and emit only water vapor as a byproduct. Fuel cells can be categorized by the type of electrolyte used, including polymer electrolyte membrane (PEM), phosphoric acid, molten carbonate, solid oxide, and alkaline aqueous solutions.

[0005] Polymer electrolyte membrane fuel cells (PEMFCs) have lower operating temperatures, higher efficiency, higher current and power densities, shorter startup times, and faster response to load changes compared to other fuel cells. Therefore, PEMFCs are considered the most suitable fuel cell for use as a power source for transportation and vehicles.

[0006] In a PEMFC, a catalyst layer containing catalyst particles is applied to both sides of a polymer electrolyte membrane, and a gas diffusion layer (GDL) is bonded to each side of the catalyst layer. A gasket that prevents gas leakage may be bonded to the edge of the gas diffusion layer to form a membrane electrode assembly (MEA). On both sides of the MEA, a microporous layer of the gas diffusion layer is bonded to the catalyst layer, and a carbon substrate of the gas diffusion layer and a bipolar plate are in close contact. Here, the gas diffusion layer (GDL) is manufactured by coating a microporous layer (MPL) on a carbon substrate made of a porous carbon material such as carbon cloth, carbon non-woven fabric, and carbon paper.

[0007] Fuel cells are being applied in a growing number of areas to combat climate change and the resulting environmental destruction caused by global warming. Consequently, their inadequate lifespan is increasingly becoming a concern. For example, while the required lifespan for hydrogen fuel cells used in passenger cars is currently around 5,000 hours, that for hydrogen fuel cells used in trucks and buses is now over 25,000 hours. Therefore, for commercial vehicles such as buses and trucks, the durability of fuel cells needs to be improved.

[0008] During fuel cell operation, components of the membrane electrode assembly, such as the electrolyte membrane through which hydrogen cations generated by electrode reactions at the fuel electrode (specifically, the hydrogen anode) move, as well as the catalyst particles and their supports, deteriorate, limiting the long-term use of the fuel cell. Deterioration of the electrolyte membrane can be categorized into chemical or electrochemical degradation and mechanical degradation. Chemical or electrochemical degradation occurs in an environment where the open-circuit potential (OCV) or the potential due to fuel mixing is continuously maintained above 1.2 V, resulting in the generation of large quantities of oxygen radicals and hydrogen peroxide due to carbon corrosion and side reactions in the catalyst support and microporous layer. These side reaction products can react with the polymer membrane, destroying part of its structure and causing its deterioration. This leads to increased resistance and reduced durability of the membrane electrode assembly. Furthermore, pinholes can form within the polymer membrane, which can lead to fuel mixing, drastically reducing stack performance and output.

[0009] In order to improve the durability of fuel cells by preventing degradation of polymer electrolyte membranes, i.e. polymer separators, caused by free radicals formed by electrochemical side reactions during operation of PEMFCs, attempts have been made to apply cerium oxide as a radical scavenger.

[0010] However, although conventional cerium oxide radical scavengers have excellent free radical scavenging activity, i.e., free radical removal performance, their scavenging activity is insufficient, so their usage amount must be increased. In this case, they can act as factors that reduce the electrochemical performance of various fuel cells, such as a decrease in the ionic conductivity of the membrane, a decrease in the mechanical durability of the membrane, and contamination of the membrane electrode assembly catalyst layer due to excessive leaching of cerium. In addition, if hygroscopic cerium oxide particles are included in the microporous layer in an excessive amount, they can suppress water discharge in the high current density operating range of the fuel cell where excessive water is generated, which can cause water flooding. Therefore, when manufacturing the microporous layer (MPL) of the gas diffusion layer for a fuel cell using a conventional cerium oxide radical scavenger, the usage amount of the radical scavenger needs to be limited, and conversely, if its usage amount is reduced, sufficient radical scavenging performance cannot be expected.

[0011] Accordingly, one object of the present disclosure is to provide a gas diffusion layer including a microporous layer containing a cerium oxide particle radical trapping agent, which has significantly improved free radical removal performance and can exhibit sufficient free radical removal performance even with a small amount of use, in order to solve the above-mentioned problems.

[0012] Another object of the present disclosure is to provide a membrane electrode assembly including a gas diffusion layer for the fuel cell, which improves cell performance and durability and suppresses water flooding in a high current density operating range, thereby expanding the available current range of the fuel cell.

[0013] Another object of the present disclosure is to provide a fuel cell having improved cell performance and durability, including a gas diffusion layer for the fuel cell.

[0014] In order to achieve the object of the present disclosure, one aspect of the present disclosure is,

[0015] A gas diffusion layer for a fuel cell, wherein the gas diffusion layer includes a carbon substrate and a microporous layer formed on the carbon substrate.

[0016] The microporous layer comprises carbon particles and a water-repellent resin that binds the carbon particles, and the microporous layer further comprises a radical scavenger selected from cerium oxide particles having a controlled particle shape.

[0017] The controlled particle shape is at least one selected from a cuboid, a cube, an octahedron, or a polyhedron having nine or more surfaces, and the cerium oxide particles provide a gas diffusion layer comprising nano-sized cerium oxide particles doped with a non-metallic element and / or a metal element.

[0018] In one embodiment, the microporous layer comprises 15 to 45 wt% of the water-repellent resin and 55 to 85 wt% of the carbon particles, and the content of the cerium oxide particles having the controlled particle shape in the microporous layer may be 0.01 wt% or more and 3.0 wt% or less relative to the weight of the carbon particles.

[0019] In one embodiment, the cerium oxide particles may be CeO2 particles having a cubic, rectangular or octahedral shape.

[0020] In one embodiment, the nano-sized cerium oxide particles can have a size of less than 100 nm, 15 nm to 70 nm, 18 nm to 60 nm, 18 nm to 50 nm, 25 nm to 50 nm, 30 nm to 45 nm, 35 nm to 44 nm, 36 nm to 44 nm, 38 nm to 44 nm, 40 nm to 44 nm, or 41 nm to 43 nm.

[0021] In one embodiment, the doped non-metallic element is at least one selected from nitrogen, phosphorus, sulfur, chlorine, and fluorine; and the doped non-metallic element may be at least one selected from La, Pr, Sm, Eu, Gd, Y, Zr, and Nb.

[0022] In one embodiment, the doping amount of the non-metallic element may be 0.1 to 3.0 atomic%, 0.2 to 3.0 atomic%, 0.3 to 3.0 atomic%, 0.4 to 3.0 atomic%, 0.5 to 2.5 atomic%, 0.6 to 2.0 atomic%, 0.7 to 1.5 atomic%, 0.8 to 1.3 atomic%, 0.8 to 1.2 atomic%, 0.8 to 1.1 atomic%, 0.8 to 1.0 atomic%, 0.9 to 1.4 atomic%, 1.0 to 1.3 atomic%, 1.1 to 1.4 atomic%, or 1.2 to 1.3 atomic% based on the doped cerium oxide particle sample.

[0023] In one embodiment, the doping amount of the metal element may be 0.1 to 3.0 atomic%, 0.2 to 3.0 atomic%, 0.3 to 3.0 atomic%, 0.4 to 3.0 atomic%, 0.2 to 2.5 atomic%, 0.3 to 2.0 atomic%, 0.4 to less than 1.5 atomic%, 0.5 to 1.4 atomic%, 0.6 to 1.3 atomic%, 0.7 to 1.2 atomic%, 0.7 to 1.1 atomic%, 0.7 to 1.0 atomic%, 0.8 to 1.2 atomic%, 0.8 to 1.1 atomic%, 0.8 to 1.0 atomic%, or 0.8 to 1.0 atomic% based on the doped cerium oxide particle sample.

[0024] In one embodiment, the cerium oxide particles are Ce 3+ ions and Ce 4+ It can contain all ions.

[0025] In one embodiment, Ce present in the cerium oxide particles and / or the doped cerium oxide particles 3+ ions and Ce4+ Ce of ion 3+ : Ce 4+ The molar ratio is in the range of 0.2:0.8 to 0.8:0.2, and the molar ratio may be a value obtained by deconvolution of peaks at the Ce 3d binding energy level on an X-ray photoelectron spectroscopy spectrum.

[0026] In one embodiment, the water-repellent resin may be a fluorinated resin and may be included in both the carbon substrate and the microporous layer.

[0027] In one embodiment, the carbon particles may be at least one selected from carbon black, activated carbon, carbon black, acetylene black, Ketjen black, Denka black, carbon whiskers, activated carbon fibers, vapor-grown carbon fibers (VGCF), carbon aerosols, carbon nanotubes, carbon nanofibers, carbon nanohorns, and graphite.

[0028] In order to achieve another object of the present disclosure, another aspect of the present disclosure provides a membrane electrode assembly for a fuel cell including a gas diffusion layer according to one aspect of the present disclosure.

[0029] In order to achieve another object of the present disclosure, another aspect of the present disclosure provides a fuel cell comprising a membrane electrode assembly according to another aspect of the present disclosure.

[0030] The radical trapping agent used when forming the microporous layer of the gas diffusion layer according to the present disclosure comprises nano-sized cerium oxide particles having a controlled particle shape selected from a rectangular parallelepiped, a cube, an octahedron, or a polyhedron having nine or more surfaces. The nano-sized cerium oxide particles having such a controlled particle shape exhibit significantly superior radical scavenging performance than nano-sized cerium oxide particles having a conventional irregular or spherical shape (hereinafter, simply referred to as “spherical”). When doped with at least one non-metallic element selected from nitrogen, phosphorus, sulfur, chlorine, and fluorine; or at least one metal element selected from La, Pr, Sm, Eu, Gd, Y, Zr, and Nb, the nano-sized cerium oxide particles having the controlled shape can exhibit further increased radical scavenging performance.

[0031] Therefore, the gas diffusion layer according to the present disclosure can exhibit sufficient free radical removal performance even though it includes a small amount of nano-sized cerium oxide particles having the above-described controlled shape. The membrane electrode assembly and fuel cell according to the present disclosure include the gas diffusion layer having the above-described excellent performance, thereby improving cell performance and durability and suppressing water flooding in a high current density operating range, thereby expanding the available current range of the fuel cell.

[0032] FIGS. 1A to 1D are scanning electron microscope (SEM) photographs showing the shapes of commercial cerium oxide particles with controlled shapes obtained in Manufacturing Examples 1 to 3 (FIGS. 1B to 1D) compared to commercial cerium oxide particles having irregular or spherical shapes in Comparative Manufacturing Example 1 (FIG. 1A).

[0033] Figure 2 is a result of comparing the RhB concentration decay rate over time measured in a Fenton's aqueous solution containing cerium oxide particles and RhB to the RhB concentration decay rate over time measured in a blank Fenton's aqueous solution not containing cerium oxide particles in order to evaluate the radical trapping activity of the cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 1 to 3.

[0034] Figures 3a and 3b are scanning electron microscope (SEM) and transmission electron microscope (TEM) images, respectively, of nitrogen-doped, cubic-shaped cerium oxide particles obtained in Manufacturing Example 6.

[0035] Figure 4 shows X-ray diffraction (XRD) patterns of undoped or nitrogen-doped cerium oxide particles of Comparative Manufacturing Examples 1 and 2, 5 to 7.

[0036] Figure 5 is a summary of the results of evaluating the radical capture activity of nitrogen-doped or undoped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and 5 to 7 using the radical capture activity evaluation method described above.

[0037] Figure 6 is a bar graph showing a relative comparison of the results of Figure 5 after 60 minutes.

[0038] Figures 7a and 7b are scanning electron microscope (SEM) photographs of phosphorus-doped, cubic-shaped cerium oxide particles obtained in Manufacturing Examples 8 and 9, respectively.

[0039] Figure 8 shows X-ray diffraction (XRD) patterns of undoped or phosphorus-doped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 2, 8, and 9.

[0040] Figure 9 is a summary of the results of evaluating the radical capture activity of doped or undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 2, 8, and 9 using the radical capture activity evaluation method described above.

[0041] Figure 10 is a bar graph showing a relative comparison of the results of Figure 9 after 60 minutes.

[0042] Figure 11 is a scanning electron microscope (SEM) photograph of lanthanum (La)-doped, cubic-shaped cerium oxide particles obtained in Manufacturing Example 10.

[0043] Figure 12 shows X-ray diffraction (XRD) patterns of undoped or lanthanum (La) doped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and 10.

[0044] Figure 13 summarizes the results of evaluating the radical capture activity of lanthanum-doped or undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 2 and 10 using the radical capture activity evaluation method described above.

[0045] Figure 14 is a bar graph showing a relative comparison of the results of Figure 13 after 60 minutes.

[0046] Figure 15 is a graph comparing i) the current-voltage curve (solid line) of a unit cell including a fresh molecular electrolyte membrane (including a catalyst layer) and a gas diffusion layer, ii) the current-voltage curve (dotted line) of a unit cell including a corroded polymer electrolyte membrane (including a catalyst layer) and a gas diffusion layer, and iii) the current-voltage curve (dashed line) of a unit cell including a fresh polymer electrolyte membrane (including a catalyst layer) and a corroded gas diffusion layer.

[0047] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way.

[0048] Hereinafter, a gas diffusion layer comprising a microporous layer including cerium oxide particles having a controlled shape and / or a radical trapping agent including doped cerium oxide particles having a controlled shape, an electrode for a fuel cell, a membrane electrode assembly, and a fuel cell according to exemplary embodiments of the present disclosure will be described in more detail. However, the description below is for illustrative purposes only. Therefore, it will be apparent to those skilled in the art that these can be variously modified and altered.

[0049] Unless otherwise explicitly stated herein, all numerical values ​​representing mechanical / thermal properties, composition percentages, dimensions and / or tolerances, or other characteristics, when describing the scope of the present disclosure, should be understood to be modified by the words "about" or "approximately." Such modifications are required for a variety of reasons, including industry practices, materials, manufacturing, assembly tolerances, and testing capabilities.

[0050] First, a description is given of cerium oxide particles having a controlled shape and / or cerium oxide particles having a controlled shape and doped, and a method for producing the same, which are radical trapping agents used in manufacturing a gas diffusion layer according to the present disclosure.

[0051] In the present disclosure, cube shape and hexahedron shape may be used interchangeably.

[0052] In the present disclosure, rod shape and rectangular parallelepiped shape may be used interchangeably.

[0053] The radical scavenger comprises cerium oxide particles having a controlled particle shape. The controlled particle shape is a rectangular parallelepiped, a cube, an octahedron, or a polyhedral having nine or more surfaces, and the cerium oxide particles are nano-sized particles.

[0054] Conventional cerium oxide particles used as radical trappers have a spherical shape, whereas the radical trapper used in the present disclosure has a controlled shape, such as a rectangular parallelepiped, a cube, an octahedron, or a polyhedron having nine or more surfaces. The inventors of the present invention have found that the free radical trapping activity, i.e., free radical scavenging performance, of cerium oxide particles having the above-mentioned controlled shape, instead of spherical cerium oxide particles, is significantly increased. Therefore, when cerium oxide particles having such a controlled shape are used in the manufacture of a microporous layer for a fuel cell, sufficient free radical scavenging performance can be exhibited even with a small amount of the used amount. Therefore, when cerium oxide particles having such a controlled shape are used, degradation of a polymer electrolyte membrane, i.e., a polymer separator, due to attack by free radicals during fuel cell operation can be effectively reduced or prevented.

[0055] The above cerium oxide particles have very different free radical capturing properties depending on their particle shape. For example, cubic cerium oxide particles have the smallest surface area but exhibit the greatest free radical capturing activity compared to rectangular parallelepipeds and octahedra, such as rod-shaped particles, or polyhedrons with nine or more faces.

[0056] The nano-sized cerium oxide particles may have a crystal size of less than 100 nm, 15 nm to 70 nm, 18 nm to 60 nm, 18 nm to 50 nm, 25 nm to 50 nm, 30 nm to 45 nm, 35 nm to 44 nm, 36 nm to 44 nm, 38 nm to 44 nm, 40 nm to 44 nm, or 41 nm to 43 nm; and a BET surface area of ​​10 to 90 m2 / g, 15 to 80 m2 / g, 18 to 70 m2 / g, 20 to 60 m2 / g, 20 to 50 m2 / g, 20 to 45 m2 / g, 20 to 40 m2 / g, or 20 to 35 m2 / g.

[0057] The crystal size (unit: nm) of the cerium oxide particles was measured using the characteristic peak of the (111) crystal plane of the crystal particles from the reflection mode X-ray diffraction (XRD) pattern (SmartLab, Rikaku) obtained by irradiating Cu-Kα radiation with a wavelength of 1.54 Å operating at 9 kW (scan rate = 6° / min).

[0058] BET (Brunauer-Emmett-Teller) surface area (unit: m2 / g) is a value measured using a BET analyzer (Tristar-II, Micromeritics) using the nitrogen gas adsorption method according to the method specified in ASTM D3663-20 (Standard Test Method for Surface Area of ​​Catalysts and Catalyst Carriers).

[0059] The above cerium oxide particles may be doped with at least one non-metal element selected from nitrogen, phosphorus, sulfur, chlorine and fluorine, specifically a non-metal anion.

[0060] The doping amount of the non-metallic element may be 0.1 to 5.0 atomic%, 0.2 to 4.0 atomic%, 0.3 to 3.5 atomic%, 0.4 to 3.0 atomic%, 0.5 to 2.5 atomic%, 0.6 to 2.0 atomic%, 0.7 to less than 1.5 atomic%, 0.8 to 1.3 atomic%, 0.8 to 1.2 atomic%, 0.8 to 1.1 atomic%, 0.8 to 1.0 atomic%, 0.9 to 1.4 atomic%, 1.0 to 1.3 atomic%, 1.1 to 1.4 atomic%, or 1.2 to 1.3 atomic% based on the cerium oxide particle sample doped with the non-metallic element.

[0061] The above cerium oxide particles may be doped with at least one metal element selected from La, Pr, Sm, Eu, Gd, Y, Zr, and Nb.

[0062] The doping amount of the metal element may be 0.1 to 3.0 atomic%, 0.2 to 2.5 atomic%, 0.3 to 2.0 atomic%, 0.4 to less than 1.5 atomic%, 0.5 to 1.4 atomic%, 0.6 to 1.3 atomic%, 0.7 to 1.2 atomic%, 0.7 to 1.1 atomic%, 0.7 to 1.0 atomic%, 0.8 to 1.2 atomic%, 0.8 to 1.1 atomic%, 0.8 to 1.0 atomic% or 0.8 to 1.0 atomic% based on the cerium oxide particle sample doped with the metal element.

[0063] Although cerium oxide particles having a controlled shape as such have improved free radical scavenging performance on their own compared to conventional spherical-shaped counterparts, they can have even more improved free radical scavenging performance when doped with the above-mentioned non-metallic elements, specifically non-metallic anions, and / or metal elements, specifically metal cations. Therefore, when cerium oxide particles having a controlled shape as such are used, deterioration of the polymer electrolyte membrane, i.e., the polymer separator, due to attack by free radicals during fuel cell operation can be more effectively reduced or prevented even when used in smaller amounts.

[0064] In particular, the use of cerium oxide particles doped with nitrogen, lanthanum, and / or phosphorus may be desirable in terms of radical scavenging performance. By including a radical scavenger in the microporous layer, the durability of the gas diffusion layer as well as the durability of the membrane electrode assembly and fuel cell employing the body diffusion layer can be improved.

[0065] The cerium oxide particles having the above-described controlled shape have improved free radical scavenging performance, and thus can exhibit sufficient free radical scavenging performance even in small amounts. For example, the content of the cerium oxide particles having the above-described controlled particle shape in the microporous layer may be 0.01 wt% or more and 3.0 wt% or less relative to the weight of the carbon particles. Specifically, the content of the cerium oxide particles having the controlled particle shape is sufficiently free even at a content of 0.01 wt% or more and 1.5 wt% or less, particularly 0.01 wt% or more and less than 1.5 wt%, for example 0.01 wt% or more and 1.4 wt% or less, 0.01 wt% or more and 1.0 wt% or less, 0.1 wt% or more and 1.0 wt% or less, 0.2 wt% or more and less than 1.5 wt%, 0.3 wt% or more and less than 1.5 wt%, 0.4 wt% or more and less than 1.5 wt%, 0.5 wt% or more and less than 1.5 wt%, 0.6 wt% or more and less than 1.5 wt%, 0.7 wt% or more and less than 1.5 wt%, 0.8 wt% or more and less than 1.5 wt%, 0.9 wt% or more and less than 1.5 wt%, or 1.0 wt% or more and less than 1.5 wt%. It can exhibit radical removal performance.

[0066] The above cerium oxide particles are Ce 3+ ions and Ce 4+ It may contain all ions, in which case, Ce present in the cerium oxide particles and / or the anion or cation doped cerium oxide particles 3+ ions and Ce 4+ Ce of ion 3+ : Ce 4+ The molar ratio may range from 0.2:0.8 to 0.8:0.2.

[0067] The above cerium oxide particles and / or doped cerium oxide particles are Ce 3+ ions and Ce 4+It is desirable to include all ions in the gas diffusion layer, and therefore, in terms of improving the durability of the MEA and fuel cell including it. Ce present in the cerium oxide particles and / or doped cerium oxide particles 3+ ions and Ce 4+ Ce of ion 3+ : Ce 4+ The molar ratio may be in the range of 0.2:0.8 to 0.8:0.2, for example, 0.3:0.7 to 0.7:0.3, 0.35:0.65 to 0.65:0.35, 0.4:0.6 to 0.6:0.4, 0.45:0.55 to 0.55:0.45, or 0.5:0.5. The molar ratio is a value obtained by deconvolution of peaks at the Ce 3d binding energy level on an X-ray photoelectron spectroscopy spectrum.

[0068] Nitrogen, lanthanum, or phosphorus elements doped onto cerium oxide particles can act as cocatalysts, promoting reactivity in the oxygen reduction reaction. They can also act as a barrier to byproducts generated within the fuel cell, such as hydrogen peroxide, from accessing carbon, thereby inhibiting chemical or electrochemical corrosion of the microporous layer and catalyst support, which are primarily composed of carbon particles.

[0069] Therefore, in membrane electrode assemblies and fuel cells employing shape-controlled cerium oxide particles and microporous layers or gas diffusion layers containing doped cerium oxide particles with controlled shapes, chemical or electrochemical degradation can be effectively prevented over a long period of time, thereby achieving excellent electrochemical performance over a long period of time. Therefore, using the cerium oxide particles as a radical scavenger leads to improved durability and extended service life of the fuel cell, and water flooding can be suppressed in a high current density operating range, thereby expanding the available current range of the fuel cell.

[0070] Next, a method for manufacturing cerium oxide particles having a controlled shape as described above and doped cerium oxide particles having a controlled shape will be described in more detail.

[0071] A method for producing a radical scavenger comprising cerium oxide particles having a controlled shape comprises the steps of: (a) adding an alkaline aqueous solution to an aqueous solution containing a cerium-containing compound and adjusting the pH of the resulting mixture solution; (b) hydrothermally reacting the mixture solution obtained in step (a) at a temperature of 90 to 160°C while stirring to form cerium oxide particles having a controlled particle shape of a rectangular parallelepiped, a cube, an octahedron, or a polyhedron having nine or more surfaces; (c) washing the cerium oxide particles using water and / or an aliphatic alcohol, such as methanol or ethanol, and drying the cerium oxide particles at a temperature of from room temperature to 100°C, from 40 to 90°C, from 50 to 80°C, from 60 to 80°C, or from 70 to 80°C; And (d) a step of calcining the cerium oxide particles in an air atmosphere at a temperature of 300 to 800°C, for example, 350 to 700°C, 380 to 600°C, 390 to 500°C, 395 to 470°C, 400 to 450°C, 400 to 430°C, or 400 to 410°C for 1 to 8 hours, 2 to 6 hours, 3 to 5 hours, or 3.5 to 4.5 hours.

[0072] In step (a), as the basic aqueous solution, for example, a NaOH and / or KOH aqueous solution having a concentration of 6.8 to 7.0 M is used, and the pH of the mixture solution is adjusted to 10 to 14, 11.5 to 13.0, 11.8 to 12.8, 11.8 to 12.6, 11.8 to 12.4, or 11.8 to 12.2, and in step (b), a hydrothermal reaction is performed at a temperature of 55°C to less than 140°C, 70°C to less than 140°C, 80°C to less than 140°C, 90°C to less than 140°C, 95°C to 130°C or less, 95°C to 120°C or less, 95°C to 110°C or less, or 95°C to 105°C or less, thereby producing cerium having a rectangular parallelepiped shape. Oxide particles can be obtained.

[0073] Alternatively, in step (a), an aqueous solution of NaOH and / or KOH having a concentration of, for example, 6.8 to 7.0 M is used as the basic aqueous solution, and the pH of the mixture solution is adjusted to 10 to 14, 11.5 to 13.0, 11.8 to 12.8, 11.8 to 12.6, 11.8 to 12.4, or 11.8 to 12.2, and in step (b), at a temperature of 140°C to 220°C, 140°C to 210°C, 140°C to 200°C, 140°C to 190°C, 140°C to 180°C, 140°C to 170°C, 150°C to 165°C, or 155°C to 165°C. By performing a hydrothermal reaction, cerium oxide particles having a cubic shape can be obtained.

[0074] Alternatively, in step (a), an aqueous solution of NaOH and / or KOH having a concentration of, for example, 0.01 to 0.02 M is used as the basic aqueous solution, and the pH of the mixture solution is adjusted to less than 8.0, 1.0 to 8.0, 2.0 to 8.0, 4.0 to 8.0, 5.0 to 7.5, 5.5 to 7.4, 6.0 to 7.3, 6.5 to 7.2, or 6.8 to 7.2, and in step (b), 140°C to 220°C, 140°C to 210°C, 140°C to 200°C, 140°C to 190°C, 140°C to 180°C, 140°C to 170°C, 150°C to 165 Cerium oxide particles having an octahedral shape can be obtained by conducting a hydrothermal reaction at a temperature of ℃ or lower, or 155 ℃ or higher and 165 ℃ or lower.

[0075] Alternatively, in step (a), a NaOH and / or KOH aqueous solution having a concentration of, for example, 0.05 to 0.2 M is used as the basic aqueous solution, and the pH of the mixture solution is adjusted to 7.5 to 11.5, 7.6 to 11.0, 7.7 to 10.0, 7.8 to 9.0, 7.8 to 8.5, or 7.8 to 8.3, and in step (b), a hydrothermal reaction is performed at a temperature of 140° C. to 180° C., 140° C. to 170° C. or less, 145° C. to 165° C. or less, 150° C. to 160° C. or less, or 155° C. to 165° C., thereby obtaining cerium oxide particles having a polyhedral shape with 9 or more surfaces.

[0076] The cerium-containing compound may be at least one selected from cerium nitrate, cerium chloride, cerium sulfate, cerium hydroxide, cerium carbonate, cerium acetate, and cerium boride. The cerium-containing compound may be in the form of a hydrate.

[0077] (b) The hydrothermal reaction in step (b) is typically carried out in a closed reactor, such as an autoclave. Therefore, the pressure within the reactor can exceed 1 atm, so the hydrothermal reaction occurs in an aqueous solution, but the hydrothermal reaction can proceed at temperatures exceeding 100°C.

[0078] In order to prepare cerium oxide particles having a controlled particle shape and doped with the above non-metallic element, in step (a), at least one non-metallic element-containing compound selected from nitrogen, phosphorus, sulfur, chlorine, and fluorine may be further added to the aqueous solution containing the cerium-containing compound. The non-metallic element-containing compound may be a carbon-based organic compound containing at least one non-metallic element selected from nitrogen, phosphorus, sulfur, chlorine, and fluorine. For example, the nitrogen-containing compound may be at least one selected from ammonia gas, an aniline-based polymer, melamine, urea, and an amine-based compound.

[0079] The above nitrogen-containing compound may be at least one phosphate compound selected from diammonium hydrogen phosphate (DAHP), dibutylammonium trihydrogen diphosphate, diammonium hydrogen phosphate (DAP), dihydrogen phosphate, monohydrogen phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, 2-ethylhexyl phosphate, and dihydrogen phosphate.

[0080] In order to manufacture cerium oxide particles having a controlled particle shape and doped with the above metal element, at least one metal element-containing compound selected from La, Pr, Sm, Eu, Gd, Y, Zr and Nb may be further added to the aqueous solution containing the cerium-containing compound in step (a).

[0081] For example, the La-containing compound may be at least one selected from lanthanum nitrate, lanthanum chloride, lanthanum sulfate, lanthanum hydroxide, lanthanum carbonate, and lanthanum acetate. The La-containing compound may be in the form of a hydrate.

[0082] The manufacturing method according to the present disclosure described above is advantageous in controlling the particle shape because it synthesizes cerium oxide particles or doped cerium oxide particles by using a hydrothermal process instead of a pyrolysis process or a microwave treatment process, and can dope the cerium oxide particles with a desired element simultaneously with the formation of the particles.

[0083] Next, a gas diffusion layer comprising a microporous layer comprising a radical trapping agent comprising cerium oxide particles having a controlled shape and / or doped cerium oxide particles having a controlled shape, an electrode for a fuel cell, a membrane electrode assembly, and a fuel cell according to exemplary embodiments of the present disclosure are described in more detail.

[0084] According to an exemplary embodiment of the present disclosure, a gas diffusion layer for a fuel cell includes a carbon substrate and a microporous layer (MPL) formed on the carbon substrate. The microporous layer includes carbon particles and a water-repellent resin that binds the carbon particles, and the microporous layer further includes a radical scavenger selected from cerium oxide particles having a controlled particle shape. The controlled particle shape is at least one selected from a rectangular parallelepiped, a cube, an octahedron, or a polyhedron having nine or more surfaces, and the cerium oxide particles are nano-sized particles. The microporous layer has a first surface bonded to the carbon substrate and a second surface facing the first surface. In the MEA, a catalyst layer is formed on the microporous layer. A lower portion of the carbon substrate is in contact with a gas flow path. The second surface may face the catalyst layer, and the first surface may face a separator.

[0085] The thickness of the microporous layer in the gas diffusion layer is not particularly limited, but may be 20 ㎛ to 200 ㎛, for example, 20 ㎛ to 150 ㎛, 30 ㎛ to 100 ㎛, 30 ㎛ to 80 ㎛, 30 ㎛ to 70 ㎛, 30 ㎛ to 60 ㎛, or 20 ㎛ to 50 ㎛. The average thickness of the carbon substrate in the gas diffusion layer is not particularly limited, but may be 20 ㎛ to 1000 ㎛, for example, 30 ㎛ to 600 ㎛, 50 ㎛ to 500 ㎛, 100 ㎛ to 450 ㎛, 100 ㎛ to 400 ㎛, 100 ㎛ to 300 ㎛, or 100 ㎛ to 280 ㎛. In addition, the basis weight of the applied microporous layer is not particularly limited, but may be 15 g / m2 to 35 g / m2, for example, 15 g / m2 to 30 g / m2, 15 g / m2 to 25 g / m2, or 15 g / m2 to 20 g / m2.

[0086] The microporous layer may comprise 15 to 45 wt%, for example 15 to 40 wt%, 15 to 35 wt%, 15.5 to 34.5 wt%, 16 to 34 wt%, 16.5 to 33.5 wt%, 17 to 33 wt%, or 18 to 32 wt% of a water-repellent resin; and 55 to 85 wt%, 60 to 85 wt%, or 65 to 85 wt%, for example 65.5 to 84.5 wt%, 66 to 84 wt%, 66.5 to 83.5 wt%, 67 to 83 wt%, or 68 to 82 wt% of carbon particles.

[0087] The microporous layer may include cerium oxide particles having the controlled particle shape in an amount of 0.01 wt% or more and 3.0 wt% or less, for example, 0.01 wt% or more and 2.5 wt% or less, 0.01 wt% or more and 2.0 wt% or less, 0.01 wt% or more and 1.5 wt% or less, 0.01 wt% or more and 1.5 wt% or less, 0.01 wt% or more and 1.4 wt% or less, 0.01 wt% or more and 1.3 wt% or less, 0.01 wt% or more and 1.2 wt% or less, 0.01 wt% or more and 1.1 wt% or less, or 0.01 wt% or more and 1.0 wt% or less, based on the weight of the carbon particles.

[0088] The microporous layer includes carbon particles and a water-repellent resin that binds the carbon particles. These components are the main materials constituting the microporous layer. The microporous layer further includes the radical scavenger described above. The radical scavenger can effectively remove hydrogen peroxide and free radicals generated by the recombination reaction of hydrogen radicals and oxygen radicals generated at the open-circuit potential or higher of the fuel cell. In particular, the use of cerium oxide particles having a controlled particle shape doped with nitrogen or lanthanum may be preferable in terms of free radical scavenging performance. By including the radical scavenger in the microporous layer as described above, the durability of the gas diffusion layer as well as the cell performance and durability of the membrane electrode assembly and fuel cell employing the gas diffusion layer are improved, and water flooding can be suppressed in a high current density operating range, thereby expanding the available current range of the fuel cell.

[0089] The above cerium oxide particles may be CeO2 particles having a cubic, rectangular or octahedral shape.

[0090] The nano-sized cerium oxide particles may have a crystal size of less than 100 nm, 15 nm to 70 nm, 18 nm to 60 nm, 18 nm to 50 nm, 25 nm to 50 nm, 30 nm to 45 nm, 35 nm to 44 nm, 36 nm to 44 nm, 38 nm to 44 nm, 40 nm to 44 nm, or 41 nm to 43 nm.

[0091] The above cerium oxide particles may be doped with at least one non-metallic element selected from nitrogen, phosphorus, sulfur, chlorine, and fluorine; or at least one metal element selected from La, Pr, Sm, Eu, Gd, Y, Zr, and Nb.

[0092] The doping amount of the non-metallic element may be 0.1 to 3.0 atomic%, 0.2 to 3.0 atomic%, 0.3 to 3.0 atomic%, 0.4 to 3.0 atomic%, 0.5 to 2.5 atomic%, 0.6 to 2.0 atomic%, 0.7 to 1.5 atomic%, 0.8 to 1.3 atomic%, 0.8 to 1.2 atomic%, 0.8 to 1.1 atomic%, 0.8 to 1.0 atomic%, 0.9 to 1.4 atomic%, 1.0 to 1.3 atomic%, 1.1 to 1.4 atomic%, or 1.2 to 1.3 atomic% based on the doped cerium oxide particle sample.

[0093] The doping amount of the metal element may be 0.1 to 3.0 atomic%, 0.2 to 3.0 atomic%, 0.3 to 3.0 atomic%, 0.4 to 3.0 atomic%, 0.2 to 2.5 atomic%, 0.3 to 2.0 atomic%, 0.4 to less than 1.5 atomic%, 0.5 to 1.4 atomic%, 0.6 to 1.3 atomic%, 0.7 to 1.2 atomic%, 0.7 to 1.1 atomic%, 0.7 to 1.0 atomic%, 0.8 to 1.2 atomic%, 0.8 to 1.1 atomic%, 0.8 to 1.0 atomic% or 0.8 to 1.0 atomic% based on the doped cerium oxide particle sample.

[0094] The above cerium oxide particles are Ce 3+ ions and Ce 4+ It can contain all ions.

[0095] Ce present in the above cerium oxide particles and / or the above doped cerium oxide particles 3+ ions and Ce 4+ Ce of ion 3+ : Ce 4+ The molar ratio is in the range of 0.2:0.8 to 0.8:0.2, and the molar ratio may be a value obtained by deconvolution of peaks at the Ce 3d binding energy level on an X-ray photoelectron spectroscopy spectrum.

[0096] The carbon substrate may be, but is not limited to, carbon paper, carbon fiber, carbon felt, carbon sheet, etc. The carbon substrate may have the thickness and pores as described above. When the gas diffusion layer according to the present invention is formed by coating a composition for a microporous layer on a carbon substrate, the carbon substrate may be specifically carbon paper, and for example, it may be carbon paper commercially available from JNTG (located in Hwaseong-si, Gyeonggi-do, Korea) under product numbers JNT18, JNT21, JNT20, JNT30, or JNT40. The carbon substrate may be impregnated with a water-repellent polymer resin and then used to manufacture the gas diffusion layer. When the carbon substrate is impregnated with a water-repellent polymer resin, the water-repellent polymer resin may have a thickness of specifically not exceeding 10 μm, specifically 1 to 5 μm, and more specifically 1 μm or less.

[0097] The above water-repellent resin may be a fluorinated resin. The water-repellent resin is not particularly limited as long as it can be combined with a carbon material such as carbon particles. The water-repellent resin may include a fluorinated resin having excellent thermal stability and water repellency, or may be made of a fluorinated resin. The fluorinated resin may be at least one selected from the group consisting of polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, a fluorinated ethylene-propylene (FEP) copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkoxy (PFA), polychlorotrifluoroethylene, an ethylene-tetrafluoroethylene (ETFE) copolymer, polyfluorovinylidene (PVDF), and a PVDF-based copolymer, but is not limited thereto.

[0098] The carbon particles may be at least one selected from carbon black, activated carbon, carbon black, acetylene black, Ketjen black, Denka black, carbon whiskers, activated carbon fibers, vapor-grown carbon fibers (VGCF), carbon aerosols, carbon nanotubes, carbon nanofibers, carbon nanohorns, and graphite. The carbon particles may be commercially available carbon blacks under the trade names Vulcan XC-72 (manufactured by Cabot Corporation), Shawinigan Black grade C55 (manufactured by Chevron Phillips Chemical Company), Furnace black N762 or Furnace black N550 (manufactured by Cancarb), or Lamp Black 101 (Orion Engineered Carbons).

[0099] A gas diffusion layer including a microporous layer having the structure described above can be manufactured using any suitable method known to those skilled in the art, such as a method of preparing a slurry composition for a microporous layer and applying the same.

[0100] The composition for the microporous layer can be prepared using any suitable materials and methods known to those skilled in the art. Accordingly, the slurry composition for the microporous layer can include the aforementioned carbon particles, a water-repellent resin such as a fluorinated resin, and radical scavenger particles.

[0101] The composition for a microporous layer may further include a dispersant and a solvent. The composition for a microporous layer may be prepared by, for example, a method including the steps of adding carbon particles and radical trapping agent particles to a solution containing a dispersant, adsorbing the solvent on the surface of the carbon particles and the surface of the radical trapping agent particles, milling or high-speed mixing so that the components such as the carbon particles and the radical trapping agent particles are finely and homogeneously dispersed at the nano- or micro-scale level; and adding a fluorinated resin such as PTFE as a water-repellent resin to the mixture and mixing so that the mixture is homogeneously dispersed.

[0102] The dispersant is not particularly limited as long as it can homogeneously disperse materials such as carbon particles and radical scavenger particles. The dispersant may be at least one selected from the group consisting of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants. Specifically, the dispersant may include, but is not limited to, 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; and nonionic surfactants such as alkylaryl polyether alcohol. Usable anionic surfactants include those commercially available under the trademarks HOSTAPAL or EMULSOGEN (manufactured by Clariant), DISPERSBYK (manufactured by BYK), or DISPERS (manufactured by TEGO), and usable nonionic surfactants include those under the trademark Triton X-100 (manufactured by Dow Chemical Company). The dispersant used should preferably be a substance that can be thermally decomposed and removed at a temperature of 250 to 400°C.

[0103] The composition for a microporous layer may vary in the content of dispersant and solvent included depending on the type of carbon particles and radical scavenger particles, and the specific surface area structure. For example, when carbon particles with a large specific surface area, such as Ketjen Black, are included, a large amount of solvent may be adsorbed within the micropores of the Ketjen Black, making dispersion difficult, and thus a large amount of dispersant may be required. On the other hand, when carbon particles with a small specific surface area, such as acetylene black, are included, a relatively small amount of solvent and dispersant may be used.

[0104] The composition for a microporous layer may include at least one solvent. For example, basic solvents such as water, n-propanol, and isopropanol may be used alone or in combination. Alternatively, a high-boiling-point solvent such as ethylene glycol, glycerol, dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and butyl acetate may be further mixed with the basic solvents mentioned above.

[0105] Methods for coating the composition for the microporous layer include spray coating, doctor blade coating, comma coating, and slot die coating, and any method may be used. The thickness of the microporous layer is not limited, and the thickness and fluororesin concentration can be varied depending on the application and stack operating conditions.

[0106] After the composition for a microporous layer is prepared, the composition for a microporous layer is applied onto a carbon substrate, dried, and sintered to form a microporous layer according to the present invention on the carbon substrate. At this time, when the slurry composition for a microporous layer is applied onto the carbon substrate and dried, some of the MPL is absorbed into the carbon substrate, and some forms a layer on the surface of the carbon substrate. A penetration passage of the MPL can be formed from the surface of the MPL to the MPL absorbed into the carbon substrate.

[0107] The fuel cell according to the present disclosure is not particularly limited as long as it includes a gas diffusion layer according to the present disclosure. Specifically, the fuel cell may include an anode, a cathode, and an electrolyte membrane, wherein the anode, or the cathode, or the anode and the cathode may include a gas diffusion layer, and the gas diffusion layer may be a gas diffusion layer according to the present disclosure.

[0108] The fuel cell may be, for example, a polymer electrolyte type, a phosphoric acid type, an alkaline aqueous solution type, etc., depending on the type of electrolyte, but the type of fuel cell is not particularly limited. According to one embodiment, the gas diffusion layer of the present disclosure is useful for manufacturing a hydrogen fuel cell for automobiles. The fuel cell may be manufactured by any suitable method known to a person skilled in the art to which the present disclosure pertains, except that it includes a gas diffusion layer according to the present disclosure.

[0109] As described above, the gas diffusion layer according to the present disclosure can exhibit sufficient free radical scavenging performance even though it includes a small amount of nano-sized cerium oxide particles having the above-described controlled shape. Therefore, the membrane electrode assembly and fuel cell according to the present disclosure include the gas diffusion layer with the above-described excellent performance, thereby improving cell performance and durability and suppressing water flooding in a high current density operating range, thereby expanding the usable current range of the fuel cell. Since the fuel cell has particularly excellent durability, the gas diffusion layer and fuel cell employing the same are useful as fuel cells for large vehicles such as buses and trucks.

[0110] Hereinafter, the present disclosure will be described in more detail using the following manufacturing examples and examples, which are provided for illustrative purposes only and are not intended to limit the present disclosure.

[0111] Manufacturing Example 1

[0112] A cerium nitrate aqueous solution was prepared by dissolving 1.736 g of Ce(NO3)3ㆍ6H2O in 10 ml of deionized water. A 6.9 M NaOH aqueous solution was prepared by dissolving 19.2 g of NaOH in 70 ml of deionized water. The two aqueous solutions were then mixed and stirred at room temperature for about 30 minutes to adjust the pH of the mixed aqueous solution to about 12.0. This mixed aqueous solution was placed in a Teflon container, which was then placed in an autoclave and stirred at about 100°C for about 24 hours to carry out a hydrothermal synthesis reaction. The obtained rod-shaped (i.e., rectangular parallelepiped) solid precipitate of cerium oxide particles was washed with deionized water and ethanol and then dried overnight in an oven maintained at about 80°C. Next, the cerium oxide particles were calcined in an air atmosphere, i.e., in the air, at a temperature of about 400°C for about 4 hours to obtain rod-shaped cerium oxide (CeO2) particles (BET specific surface area: 73.4 m2 / g).

[0113] Manufacturing Example 2

[0114] A cerium nitrate aqueous solution was prepared by dissolving 1.736 g of Ce(NO3)3ㆍ6H2O in 10 ml of deionized water. A 6.9 M NaOH aqueous solution was prepared by dissolving 19.2 g of NaOH in 70 ml of deionized water. The two aqueous solutions were then mixed and stirred at room temperature for about 30 minutes to adjust the pH of the mixed aqueous solution to about 12.0. This mixed aqueous solution was placed in a Teflon container, which was then placed in an autoclave and stirred at about 160°C for about 24 hours to carry out a hydrothermal synthesis reaction. The obtained cube-shaped (i.e., cubic) solid precipitate of cerium oxide particles was washed with deionized water and ethanol and then dried overnight in an oven maintained at about 80°C. Next, the cerium oxide particles were calcined in an air atmosphere, i.e., in the air, at a temperature of about 400°C for about 4 hours to obtain cube-shaped cerium oxide (CeO2) particles (BET specific surface area: 22.1 m2 / g).

[0115] Manufacturing Example 3

[0116] A cerium nitrate aqueous solution was prepared by dissolving 1 g of Ce(NO3)3ㆍ6H2O in 10 ml of deionized water. Approximately 0.01 M NaOH aqueous solution was prepared by dissolving 0.02 g of NaOH in 50 ml of deionized water. The two aqueous solutions were then mixed and stirred at room temperature for about 30 minutes to adjust the pH of the mixed aqueous solution to about 7.0. This mixed aqueous solution was placed in a Teflon container, which was then placed in an autoclave and stirred at about 160°C for about 24 hours to carry out a hydrothermal synthesis reaction. The obtained octahedral-shaped cerium oxide particle solid precipitate was washed with deionized water and ethanol and then dried overnight in an oven maintained at about 80°C. Next, the cerium oxide particles were calcined in an air atmosphere, i.e., in the air, at a temperature of about 400°C for about 4 hours to obtain octahedral-shaped cerium oxide (CeO2) particles (BET specific surface area: 68.9 m2 / g).

[0117] Manufacturing Example 4

[0118] A cerium nitrate aqueous solution was prepared by dissolving 1.953 g of Ce(NO3)3ㆍ6H2O in 10 ml of deionized water. An approximately 0.1 M NaOH aqueous solution was prepared by dissolving 0.32 g of NaOH in 80 ml of deionized water. The two aqueous solutions were then mixed and stirred at room temperature for approximately 30 minutes to adjust the pH of the mixed aqueous solution to approximately 8.0. This mixed aqueous solution was placed in a Teflon container, which was then placed in an autoclave and stirred at approximately 160°C for approximately 24 hours to carry out a hydrothermal synthesis reaction. The obtained polyhedral-shaped cerium oxide particle solid precipitate with nine or more faces was washed with deionized water and ethanol and then dried overnight in an oven maintained at approximately 80°C. Next, the cerium oxide particles were calcined in an air atmosphere, i.e., in the air, at a temperature of about 400°C for about 4 hours to obtain polyhedral-shaped cerium oxide (CeO2) particles (BET specific surface area: 9.2 m2 / g).

[0119] Comparative Manufacturing Example 1

[0120] The evaluation described below was conducted using commercial cerium oxide particles (Sigma-Aldrich) with a spherical shape and a BET surface area of ​​31.8 m2 / g.

[0121] Figures 1a to 1d are scanning electron microscope (SEM) photographs showing the morphology of shape-controlled commercial cerium oxide particles obtained in Manufacturing Examples 1 to 3 (Figures 1b to 1d) compared to commercial cerium oxide particles having a spherical shape in Comparative Manufacturing Example 1 (Figure 1a). The photographs were obtained using a scanning electron microscope (SEM, SNE-3000M, SEC) operating at an acceleration voltage of 30 kV equipped with an Energy Dispersive X-ray Spectometer (EDS) system.

[0122] Referring to FIGS. 1A to 1D, it can be confirmed that the shape-controlled cerium oxide particles obtained in Manufacturing Examples 1 to 3 have a rod shape, a cube shape, or an octahedral shape, respectively, compared to the commercial cerium oxide particles having a spherical shape of Comparative Manufacturing Example 1.

[0123] [Radical capture activity evaluation method]

[0124] The radical scavenging activity of cerium oxide particles was evaluated by UV-Vis analysis of the change in RhB concentration over time in Fenton's aqueous solution in the presence of rhodamine-B (RhB) as an indicator and a radical scavenger in the aqueous solution.

[0125] The Fenton reaction is a reaction that uses an iron catalyst to decompose hydrogen peroxide to generate free radicals (reaction equations (1) and (2) below). Rhodamine-B (RhB), which has a red color, is added as an indicator to the Fenton solution. The radicals formed by the Fenton reaction can destroy RhB molecules in the Fenton solution (reaction equation (3) below). Therefore, by adding a sample of the radical scavenger to be evaluated to the Fenton solution and measuring the change in RhB concentration over time, the radical scavenging activity of the sample can be relatively evaluated. If the activity of the radical scavenger is excellent, the destruction of RhB molecules by free radicals will be reduced, and the RhB concentration in the solution will be maintained above a certain level.

[0126]

[0127] Specifically, first, 0.6 mg of RhB and 3 mg of FeSO4 were dissolved in 100 mL of deionized water to obtain aqueous solution A. After placing 50 mg of a cerium oxide particle sample for which radical scavenging activity was to be evaluated in a glass vial, 2 mL of aqueous solution A was added to the glass vial with stirring.

[0128] Second, an aqueous H2O2 solution (0.08 vol%) was prepared using H2O2 (30 wt%) and deionized water. Then, 3 μL of the aqueous H2O2 solution was added dropwise to aqueous solution A in a glass vial, stirred for 15 seconds, allowed to react for 10 minutes, and then the UV-Vis spectrum was measured. The UV-Vis spectrum of this aqueous solution mixture was obtained using a UV-Vis spectrometer (Mega-800, Sinco) in the range of 300 to 700 nm. 3 μL of the aqueous H2O2 solution was added dropwise at 10-minute intervals for 60 minutes, and the above process was repeated, measuring the absorption peak intensity at 550 nm every 10 minutes to measure the change in RhB concentration in the aqueous solution mixture. Comparing the UV-Vis spectra measured seven times at 10-minute intervals for 60 minutes, the intensity of the absorption peak at 550 nm, which is due to the light absorption of RhB molecules, rapidly attenuated over time. This indicates that RhB molecules were degraded by hydroxyl radicals generated by the Fenton reaction, leading to a rapid decrease in the RhB concentration. In other words, the intensity of the absorption peak at 550 nm at a specific time is correlated with the RhB concentration at that time.

[0129] The radical trapping activity of a cerium oxide particle sample can be relatively evaluated from the decay rate of the RhB concentration in the Fenton's aqueous solution containing the cerium oxide particle sample, compared to the decay rate of the RhB concentration in a blank Fenton's aqueous solution to which no radical trapping agent is added.

[0130] Figure 2 is a result of comparing the RhB concentration decay rate over time measured in a Fenton's aqueous solution containing cerium oxide particles and RhB to the RhB concentration decay rate over time measured in a blank Fenton's aqueous solution not containing cerium oxide particles in order to evaluate the radical trapping activity of the cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 1 to 3.

[0131] Referring to Figure 2, the x-axis represents time elapsed, and the y-axis represents relative absorption (Abs / Abs0), which is obtained by dividing the absorption peak intensity Abs at 550 nm of the Fenton's aqueous solution measured every 10 min by the absorption peak intensity Abs0 at 550 nm measured at the beginning (t = 0 min) of the Fenton's aqueous solution. Therefore, the y-axis represents the relative RhB concentration (C) in a particular Fenton's aqueous solution. t / C0) indicates C t is the RhB concentration after a specific time, and C0 is the initial RhB concentration.

[0132] Referring to FIG. 2, it can be confirmed that the RhB concentration of the Fenton solution containing the conventional commercial cerium oxide particles (a) of Comparative Manufacturing Example 1 and the Fenton solution containing any one of the shape-controlled cerium oxide particles (b) to (d) according to Manufacturing Examples 1 to 3 are both much higher than the RhB concentration of the blank Fenton solution after 60 minutes. Therefore, although the conventional commercial cerium oxide particles (a) of Comparative Manufacturing Example 1 and the shape-controlled cerium oxide particles (b) to (d) according to Manufacturing Examples 1 to 3 both exhibit radical capturing activity, it can be confirmed that the shape-controlled cerium oxide particles (b) to (d) according to Manufacturing Examples 1 to 3 have higher radical removal performance than the conventional commercial cerium oxide particles (a) of Comparative Manufacturing Example 1. Among them, it can be seen that the cubic cerium oxide particle (c) of Manufacturing Example 2 has a much higher radical scavenging activity than the octahedral cerium oxide particle (d) of Manufacturing Example 3 and the rod-shaped cerium oxide particle (b) of Manufacturing Example 1, even though it has the smallest specific surface area. This is presumed to be because the cubic cerium oxide particle (c) has a small specific surface area, but its exposed crystal plane is formed as a (100) plane, which has the highest radical scavenging activity.

[0133] Therefore, below, the doping effect of non-metallic or metallic elements on cubic cerium oxide particles is investigated.

[0134]

[0135] *Manufacturing Example 5

[0136] An aqueous solution containing cerium nitrate and urea was prepared by dissolving 1.736 g of Ce(NO3)3ㆍ6H2O and 0.0913 g of urea in 10 ml of deionized water. Approximately 6.9 M NaOH aqueous solution was prepared by dissolving 19.2 g of NaOH in 70 ml of deionized water. Afterwards, the two aqueous solutions were mixed and stirred at room temperature for about 30 minutes to adjust the pH of the mixed solution to about 12.0. After placing this mixed aqueous solution in a Teflon container, the Teflon container was placed in an autoclave and stirred at a temperature of about 160°C for about 24 hours to carry out a hydrothermal synthesis reaction. The obtained nitrogen-doped cube-shaped cerium oxide particle precipitate was washed with deionized water and ethanol and then dried overnight in an oven maintained at about 80°C. Next, the nitrogen-doped cerium oxide particles were calcined in a nitrogen atmosphere at a temperature of about 400°C for about 4 hours to obtain cube-shaped nitrogen-doped cerium oxide (CeO2) particles. Various physical characteristics of the obtained particles can be confirmed in Table 1 below.

[0137] Manufacturing Example 6

[0138] Cube-shaped nitrogen-doped cerium oxide (CeO2) particles were obtained by using the same method as in Preparation Example 5, except that 0.1554 g of urea was used instead of 0.0913 g of urea when preparing an aqueous solution containing cerium nitrate and urea. Various physical characteristics of the obtained particles can be confirmed in Table 1 below.

[0139] Manufacturing Example 7

[0140] Cube-shaped nitrogen-doped cerium oxide (CeO2) particles were obtained by using the same method as in Preparation Example 5, except that 0.328 g of urea was used instead of 0.0913 g of urea when preparing an aqueous solution containing cerium nitrate and urea. Various physical characteristics of the obtained particles can be confirmed in Table 1 below.

[0141] Figures 3a and 3b are scanning electron microscope (SEM) and transmission electron microscope (TEM) images, respectively, of nitrogen-doped, cubic cerium oxide particles obtained in Preparation Example 6. The SEM images were obtained using a scanning electron microscope (SEM, SNE-3000M, SEC) operating at an acceleration voltage of 30 kV, and the TEM images were obtained using a transmission electron microscope (HR-TEM, FEI Double Cs-corrected Titan Temis TEM) operating at an acceleration voltage of 300 kV. Referring to Figures 3a and 3b, crystal grains of the nitrogen-doped, cubic cerium oxide particles can be confirmed. In addition, it can be confirmed that N atoms are uniformly doped at atomic levels within the cerium oxide crystal structure.

[0142] Figure 4 shows X-ray diffraction (XRD) patterns of undoped or nitrogen-doped cerium oxide particles of Comparative Manufacturing Examples 1 and 2, 5 to 7. The X-ray diffraction (XRD) patterns are reflection mode X-ray diffraction (XRD) patterns (SmartLab, Rikaku) obtained by irradiating Cu-Kα radiation having a wavelength of 1.54 Å operating at 3 kW (scan rate = 6° / min, step = 0.04°).

[0143] Referring to FIG. 4, the nitrogen-doped cubic cerium oxide particle samples of Preparation Examples 5 to 7 exhibit characteristic diffraction peaks of crystalline cerium oxide, similar to the spherical cerium oxide particle sample of Comparative Preparation Example 1 and the undoped cubic cerium oxide particle sample of Preparation Example 2. The average crystallite sizes of the nitrogen-doped cubic cerium oxide particle samples of Preparation Examples 5 to 7, obtained by applying the Scherrer equation using the characteristic diffraction peaks of the (111) crystal planes of these crystalline particles, were all approximately 41.6 nm. These values ​​are the same as the average crystallite sizes of the undoped cubic cerium oxide particle sample of Preparation Example 2.

[0144] The lattice parameter calculated from the characteristic diffraction peak of the (111) crystal plane of the nitrogen-doped cubic cerium oxide particle samples of Preparation Examples 5 to 7 was approximately 0.5403 to 0.5404 nm. This was slightly smaller than 0.5410 nm of the undoped cubic cerium oxide particle sample of Preparation Example 2. This is presumed to be due to lattice contraction of the cerium oxide crystal due to nitrogen doping.

[0145] The average crystal size and lattice constant of the nitrogen-doped or undoped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and Manufacturing Examples 5 to 7 mentioned above are summarized in Table 1 below. The BET (Brunauer-Emmett-Teller) surface areas (unit: m2 / g) also included in Table 1 are the values ​​measured using a BET analyzer (Tristar-II, Micromeritics) by applying the BET model using the nitrogen gas adsorption method according to the method specified in ASTM D3663-20 (Standard Test Method for Surface Area of ​​Catalysts and Catalyst Carriers). The BET surface areas of the nitrogen-doped cerium oxide particles of Manufacturing Examples 5 to 7 were smaller than those of the spherical cerium oxide particles of Comparative Manufacturing Example 1, but slightly increased than those of the undoped cerium oxide particles of Manufacturing Example 2.

[0146] Average crystal size (nm) Lattice constant (nm) BET specific surface area (m2 / g) Manufacturing example 241.60.541022.1 Manufacturing example 541.60.540325.1 Manufacturing example 641.60.540525.3 Manufacturing example 741.60.540322.6 Comparative manufacturing example 126.00.540831.8

[0147] Atomic composition (atomic %) of nitrogen-doped or undoped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and 5 to 7 mentioned above and Ce 3+ and Ce 4+ The atomic content ratios are summarized in Table 2 below.

[0148] The surface compositions of these samples were measured by X-ray photoelectron spectroscopy (XPS) using monochromatic Al-Kα radiation (Theta Probe AR-XPS, Thermo Fisher Scientific). Ce of the samples 3+ and Ce 4+The atomic content was obtained by deconvolution of peaks at the Ce 3d binding energy level. The N atomic content of nitrogen-doped samples was obtained by deconvoluting the N 1s peaks of the XPS spectra.

[0149] Referring to Table 2, the nitrogen content on the surface of the nitrogen-doped cerium oxide particles of Preparation Examples 5 to 7 was measured to be at the level of 0.8 to 1.0 atomic%. In order to investigate the oxidation state of the cerium atoms constituting these samples, Ce 3+ and Ce 4+ The concentration was analyzed. Nitrogen-doped cerium oxide particles of Preparation Examples 5 to 7 were Ce 3+ The undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Example 2 were observed to have a level of about 39 to 43%, and the undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Example 2 were observed to have a level of about 37 to 42%.

[0150] Atomic composition (atomic %)Ce 3+ and Ce 4+ Atomic content ratio (%)CeONCCe 3+ Ce 4+ Manufacturing Example 219.363.3-17.40.370.63 Manufacturing Example 520.760.60.817.90.390.61 Manufacturing Example 620.860.10.718.40.440.56 Manufacturing Example 719.260.11.019.70.430.57 Comparative Manufacturing Example 118.751.6-29.70.420.58

[0151] From the SEM, TEM, XRD, and XPS results examined above, it was confirmed that nitrogen-doped cubic cerium oxide nanoparticles were manufactured through the methods of Manufacturing Examples 5 to 7.

[0152] Figure 5 summarizes the results of evaluating the radical capture activity of nitrogen-doped or undoped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and 5 to 7 using the radical capture activity evaluation method described above. As in Figure 2, the x-axis is the time axis and the y-axis is the relative absorption rate (Abs / Abs0), i.e., the relative RhB concentration (C t / C0) is indicated.

[0153] Figure 6 is a bar graph showing a relative comparison of the results of Figure 5 after 60 minutes.

[0154] Referring to FIGS. 5 and 6, in the blank solution without the radical scavenger, the RhB concentration in the solution decreased to about 8% of the initial concentration after 60 minutes of reaction. This indicates that most RhB molecules were destroyed by free radicals generated by the Fenton reaction. In the case of Comparative Manufacturing Examples 1 and 2, the RhB concentration in the solution decreased to about 38 to 60% of the initial concentration after 60 minutes of reaction. In the case of Manufacturing Examples 5 to 7 using nitrogen-doped cerium oxide particles, the RhB concentration in the solution showed minimal change compared to the initial concentration after 60 minutes of reaction. This indicates that nitrogen-doped cubic cerium oxide nanoparticles can prevent the destruction of RhB molecules by removing free radicals more effectively than cubic cerium oxide nanoparticles.

[0155] Manufacturing Example 8

[0156] 1.736 g of Ce(NO3)3ㆍ6H2O was dissolved in 5 ml of deionized water, and 0.0296 g of diammonium hydrogen phosphate (DAHP) was dissolved in another 5 ml of deionized water, and then mixed to prepare an aqueous solution containing cerium nitrate and DAHP. 19.2 g of NaOH was dissolved in 70 ml of deionized water to prepare an approximately 6.9 M NaOH aqueous solution. The two aqueous solutions were then mixed and stirred at room temperature for about 30 minutes to adjust the pH of the mixed solution to about 12.0. This mixed aqueous solution was placed in a Teflon container, which was then placed in an autoclave and stirred at about 160°C for about 24 hours to carry out a hydrothermal synthesis reaction. The obtained phosphorus-doped cube-shaped cerium oxide particle precipitate was washed with deionized water and ethanol and then dried overnight in an oven maintained at about 80°C. Next, the phosphorus (P)-doped cerium oxide particles were calcined in an air atmosphere at a temperature of about 400°C for about 4 hours to obtain cube-shaped phosphorus-doped cerium oxide (CeO2) particles. Various physical characteristics of the obtained particles can be confirmed in Table 3 below.

[0157] Manufacturing Example 9

[0158] Cube-shaped phosphorus (P)-doped cerium oxide (CeO2) particles were obtained by using the same method as in Preparation Example 8, except that 0.0907 g of DAHP was used instead of 0.0296 g of DAHP when preparing an aqueous solution containing cerium nitrate and DAHP. Various physical characteristics of the obtained particles can be confirmed in Table 3 below.

[0159] Figures 7a and 7b are scanning electron microscope (SEM) images of phosphorus-doped, cubic cerium oxide particles obtained in Manufacturing Examples 8 (PEX 8) and 9 (PEX 9), respectively. It can be confirmed that P atoms are uniformly doped at the atomic level within the cerium oxide crystal structure.

[0160] Referring to FIGS. 7a and 7b, crystal grains of cerium oxide particles having a cubic shape doped with phosphorus (P) can be confirmed.

[0161] Figure 8 shows X-ray diffraction (XRD) patterns of undoped or phosphorus-doped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 2, 8, and 9.

[0162] Referring to FIG. 8, the phosphorus-doped cubic cerium oxide particle samples of Preparation Examples 8 and 9 exhibit characteristic diffraction peaks of crystalline cerium oxide, similar to the spherical cerium oxide particle sample of Comparative Preparation Example 1 and the undoped cubic cerium oxide particle sample of Preparation Example 2. The average crystallite sizes of the phosphorus-doped cubic cerium oxide particle samples of Preparation Examples 8 and 9, obtained by applying the Scherrer equation using the characteristic diffraction peaks of the (111) crystal plane of these crystalline particles, were approximately 34.7 and 26.0 nm, respectively. These values ​​are somewhat different from the average crystallite size of the undoped cubic cerium oxide particle sample of Preparation Example 2. This suggests that when phosphorus (P) is doped, the cerium oxide particles are not simply doped with phosphorus, but are converted into CePO4 particles.

[0163] The lattice constants calculated from the characteristic diffraction peaks of the (111) crystal plane of the phosphorus-doped cubic cerium oxide particle samples of Preparation Examples 8 and 9 were approximately 0.5393 and 0.5405 nm, respectively. This was slightly smaller than 0.5410 nm of the undoped cubic cerium oxide particle sample of Preparation Example 2. This is presumed to be due to the lattice shrinkage of the cerium oxide crystal due to phosphorus doping. The results show that P atoms were uniformly doped at atomic levels within the cerium oxide crystal structure.

[0164] The average crystal size, lattice constant, and BET specific surface area of ​​the phosphorus-doped cerium oxide particles of Preparation Examples 8 and 9 mentioned above are summarized in Table 3 below. The BET specific surface area of ​​the phosphorus-doped cerium oxide particles of Preparation Examples 8 and 9 was approximately 22 to 33 m2 / g.

[0165] Average crystal size (nm) Lattice constant (nm) BET specific surface area (m2 / g) Manufacturing example 241.6 0.5 410 22.1 Manufacturing example 834.7 0.5 39 321.7 Manufacturing example 926.0 0.5 40 533.1 Comparative manufacturing example 126.0 0.5 40 831.8

[0166] Atomic composition (atomic %) of the doped or undoped cerium oxide particles of Comparative Manufacturing Examples 1 and 2, 8 and 9 mentioned above and Ce 3+ and Ce 4+ The atomic content ratios are summarized in Table 4 below.

[0167] The surface compositions of these samples were measured by X-ray photoelectron spectroscopy (XPS) using monochromatic Al-Kα radiation (Theta Probe AR-XPS, Thermo Fisher Scientific). Ce of the samples 3+ and Ce 4+ The atomic content was obtained by deconvolution of peaks at the Ce 3d binding energy level. The P atomic content of the phosphorus-doped samples was obtained by deconvoluting the P 2p peaks of the XPS spectra.

[0168] Referring to Table 4, the phosphorus content of the phosphorus-doped cerium oxide particles of Preparation Examples 8 and 9 was measured to be at the level of 1.2 to 1.3 atomic%. In order to investigate the oxidation state of the cerium atoms constituting these samples, Ce 3+ and Ce 4+ The concentration was analyzed. The doped cerium oxide particles of Preparation Examples 8 and 9 were Ce 3+The undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Example 2 were observed to have a level of about 37 to 39%, and the undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Example 2 were observed to have a level of about 37 to 42%.

[0169] Atomic composition (atomic %)Ce 3+ and Ce 4+ Atomic content ratio (%)CeOPCCe 3+ Ce 4+ Manufacturing Example 219.363.3-17.40.370.63 Manufacturing Example 815.067.01.216.80.420.58 Manufacturing Example 918.864.61.315.30.390.61 Comparative Manufacturing Example 118.751.6-29.70.420.58

[0170] From the SEM, XRD, and XPS results examined above, it was confirmed that doped cubic cerium oxide nanoparticles were manufactured through the methods of Manufacturing Examples 8 and 9.

[0171] Figure 9 shows the results of evaluating the radical capture activity of the doped or undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 2, 8, and 9 using the radical capture activity evaluation method described above. As in Figure 2, the x-axis is the time axis, and the y-axis is the relative absorption rate (Abs / Abs0), i.e., the relative RhB concentration (C t / C0) is indicated.

[0172] Figure 10 is a bar graph showing a relative comparison of the results of Figure 9 after 60 minutes.

[0173] Referring to Figures 9 and 10, in the blank solution without the radical scavenger, the RhB concentration in the solution decreased to about 8% of the initial concentration after 60 minutes of reaction. This indicates that most RhB molecules were destroyed by free radicals generated by the Fenton reaction. In the case of Comparative Manufacturing Examples 1 and 2, the RhB concentration in the solution decreased to about 38 to 60% of the initial concentration after 60 minutes of reaction. In the case of Manufacturing Examples 8 and 9 using phosphorus-doped cerium oxide particles, the RhB concentration in the solution after 60 minutes of reaction was maintained at more than 90% of the initial concentration, showing minimal change. This indicates that phosphorus-doped cubic cerium oxide nanoparticles can prevent the destruction of RhB molecules by removing free radicals more effectively than cubic cerium oxide nanoparticles.

[0174] Manufacturing Example 10

[0175] An aqueous solution containing cerium nitrate and lanthanum nitrate was prepared by dissolving 1.736 g of Ce(NO3)3ㆍ6H2O and 30.066 g of La(NO3) in 10 ml of deionized water. An approximately 6.9 M NaOH aqueous solution was prepared by dissolving 19.2 g of NaOH in 70 ml of deionized water. The two aqueous solutions were then mixed and stirred at room temperature for about 30 minutes to adjust the pH of the mixed solution to about 12.0. This mixed aqueous solution was placed in a Teflon container, which was then placed in an autoclave and stirred at about 160°C for about 24 hours to carry out a hydrothermal synthesis reaction. The obtained lanthanum-doped cube-shaped cerium oxide particle precipitate was washed with deionized water and ethanol and then dried overnight in an oven maintained at about 80°C. Next, the lanthanum (La)-doped cerium oxide particles were calcined in an air atmosphere at a temperature of about 400°C for about 4 hours to obtain cube-shaped lanthanum (La)-doped cerium oxide (CeO2) particles. Various physical characteristics of the obtained particles can be confirmed in Table 3 below.

[0176] Fig. 11 is a scanning electron microscope (SEM) photograph of lanthanum (La)-doped, cubic-shaped cerium oxide particles obtained in Manufacturing Example 10. Referring to Fig. 11, crystal grains of the lanthanum (La)-doped, cubic-shaped cerium oxide particles can be confirmed.

[0177] Figure 12 shows X-ray diffraction (XRD) patterns of undoped or lanthanum (La) doped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and 10.

[0178] Referring to FIG. 12, the lanthanum-doped cubic cerium oxide particle samples of Preparation Example 10 exhibit characteristic diffraction peaks of crystalline cerium oxide, similar to the spherical cerium oxide particle sample of Comparative Preparation Example 1 and the undoped cubic cerium oxide particle sample of Preparation Example 2. The average crystal size of the lanthanum-doped cubic cerium oxide particle samples of Preparation Example 10, obtained by applying the Scherrer equation using the characteristic diffraction peak of the (111) crystal plane of these crystal particles, was about 41.6 nm.

[0179] The lattice constant calculated from the characteristic diffraction peak of the (111) crystal plane of the lanthanum-doped cubic cerium oxide particle samples of Preparation Example 10 was approximately 0.5404 nm. This was slightly smaller than 0.5410 nm of the undoped cubic cerium oxide particle sample of Preparation Example 2 and 0.5408 nm of the undoped spherical cerium oxide particle sample of Comparative Preparation Example 1. This is presumed to be due to lattice shrinkage of the cerium oxide crystal due to lanthanum doping. The results show that La atoms are uniformly doped at atomic levels within the cerium oxide crystal structure.

[0180] The average crystal size, lattice constant, and BET specific surface area of ​​the lanthanum-doped cerium oxide particles of Manufacturing Example 10 mentioned above are summarized in Table 5 below. The BET specific surface area of ​​the lanthanum-doped cerium oxide particles of Manufacturing Example 10 was approximately 18.4 m2 / g.

[0181] Average crystal size (nm) Lattice constant (nm) BET specific surface area (m2 / g) Manufacturing example 241.6 0.5 41022.1 Manufacturing example 1041.6 0.5 40418.4 Comparative manufacturing example 126.0 0.5 40831.8

[0182] Atomic composition (atomic %) and Ce of the lanthanum-doped or undoped cerium oxide particles of Comparative Manufacturing Examples 1 and 2 and 10 mentioned above 3+and Ce 4+ The atomic content ratios are summarized in Table 6 below. The surface compositions of these samples were measured by X-ray photoelectron spectroscopy (XPS) using monochromatic Al-Kα radiation (Theta Probe AR-XPS, Thermo Fisher Scientific). The Ce of the samples 3+ and Ce 4+ The atomic content was obtained by deconvolution of peaks at the Ce 3d binding energy level. The La atomic content of the lanthanum-doped samples was obtained by deconvoluting the La 3d peaks of the XPS spectra.

[0183] Referring to Table 6, the La atomic content of the lanthanum-doped cerium oxide particles of Manufacturing Example 10 was measured to be at the level of 0.7 atomic%. In order to investigate the oxidation state of the cerium atoms constituting these samples, Ce 3+ and Ce 4+ The concentration was analyzed. The lanthanum-doped cerium oxide particles of Preparation Example 10 were Ce 3+ The undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Example 2 were observed to have an average yield of about 36%, and the undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Example 2 were observed to have an average yield of about 37 to 42%.

[0184] Atomic composition (atomic %)Ce 3+ and Ce 4+ Atomic content ratio (%)CeOLaCCe 3+ Ce 4+ Manufacturing Example 219.363.3-17.40.370.63 Manufacturing Example 1016.964.70.714.70.360.64 Comparative Manufacturing Example 118.751.6-29.70.420.58

[0185] From the SEM, XRD, and XPS results examined above, it was confirmed that doped cubic cerium oxide nanoparticles were manufactured using the method of Manufacturing Example 10.

[0186] Figure 13 summarizes the results of evaluating the radical capture activity of lanthanum-doped or undoped cerium oxide particles of Comparative Manufacturing Example 1 and Manufacturing Examples 2 and 10 using the radical capture activity evaluation method described above. As in Figure 2, the x-axis is the time axis, and the y-axis is the relative absorption rate (Abs / Abs0), i.e., the relative RhB concentration (C t / C0) is indicated.

[0187] Figure 14 is a bar graph showing a relative comparison of the results of Figure 13 after 60 minutes.

[0188] Referring to FIGS. 13 and 14, in the case of Manufacturing Example 10 using lanthanum-doped cerium oxide particles, the concentration of RhB in the solution was maintained at more than 95% of the initial concentration after 60 minutes of reaction, showing minimal change. This indicates that cubic cerium oxide nanoparticles doped with lanthanum can more effectively remove free radicals and prevent the destruction of RhB molecules than cubic cerium oxide nanoparticles.

[0189] Next, a method for manufacturing a gas diffusion layer using cerium oxide particles having a controlled shape that can be manufactured as described above or cerium oxide particles having a conventional spherical shape as a radical trapping agent is specifically described.

[0190] Comparative Example 1

[0191] (1) Preparation of composition for microporous layer: 479 g of deionized water and 0.5 g of nonionic dispersant (Triton X-100) were mixed in a mixing tank. Conductive carbon particles with a specific surface area of ​​about 250 m were added to the solution. 2 / g and 68 g of carbon black (CB) with an average primary particle size of approximately 30 nm were mixed. 53.4 g (solid content 32 g) of polytetrafluoroethylene (PTFE) emulsion (PTFE content 60%) as a water-repellent resin was mixed into the mixture.

[0192] (2) Preparation of gas diffusion layer: The above PTFE emulsion (PTFE content 60 wt%) was diluted with deionized water to adjust the PTFE content to 5 wt%, and carbon paper (manufacturer: JNTG, product name: JNT17BB2) having a thickness of about 150 μm was immersed in the PTFE emulsion to coat the carbon paper so that the PTFE content became about 10 wt%. This was dried at 120°C to obtain a water-repellent carbon substrate coated with a fluorine resin. Subsequently, the composition for a microporous layer obtained above was applied onto one surface of the water-repellent carbon substrate by discharging it at a constant pressure using a slot die coater, and the basis weight of the applied microporous layer was set to 20 to 30 g / m2. Thereafter, the water-repellent carbon substrate was dried in a drying oven having a temperature distribution of 100°C to 130°C for about 20 minutes. This result was sintered at a temperature of 350°C for approximately 20 minutes in an air atmosphere to obtain a gas diffusion layer (GDL) in which a microporous layer was laminated on top of a water-repellent carbon substrate.

[0193] Comparative Example 2

[0194] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles and 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g (1.0 wt% relative to the weight of the conductive carbon particles) of commercially available cerium oxide particles (Comparative Manufacturing Example 1) having a spherical shape were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1, except that this was mixed.

[0195] Comparative Example 3

[0196] In the preparation step of the composition for a microporous layer, 65.96 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 2.04 g (3.0 wt% relative to the weight of the conductive carbon particles) of commercially available cerium oxide particles (Comparative Manufacturing Example 1) having a spherical shape were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1, except that this was mixed.

[0197] Comparative Example 4

[0198] In the preparation step of the composition for a microporous layer, 63.24 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 4.76 g (7.53 wt% relative to the weight of the conductive carbon particles) of commercially available cerium oxide particles (Comparative Manufacturing Example 1) having a spherical shape were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0199] Example 1

[0200] In the preparation step of the composition for a microporous layer, a GDL was manufactured in the same manner as in Comparative Example 1, except that 67.99 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) and 0.01 g of cube-shaped cerium oxide (CeO2) particles (Manufacturing Example 2) (0.01 wt% relative to the weight of the conductive carbon particles) were mixed.

[0201] Example 1-1

[0202] In the preparation step of the composition for a microporous layer, 67.99 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.01 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 6; N 0.7 at%) (0.01 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0203] Example 1-2

[0204] In the preparation step of the composition for a microporous layer, 67.99 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.01 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 5; N 0.8 at%) (0.01 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0205] Example 2

[0206] In the preparation step of the composition for a microporous layer, 67.97 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.03 g of cube-shaped cerium oxide (CeO2) particles (Preparation Example 3) (0.04 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1.

[0207] Example 3

[0208] In the preparation step of the composition for a microporous layer, 67.93 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.07 g of cube-shaped cerium oxide (CeO2) particles (Preparation Example 3) (0.1 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1.

[0209] Example 4

[0210] In the preparation step of the composition for a microporous layer, 67.66 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.34 g of cube-shaped cerium oxide (CeO2) particles (Preparation Example 3) (0.5 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1.

[0211] Example 4-1

[0212] In the preparation step of the composition for a microporous layer, 67.66 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.34 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 6; N 0.7 at%) (0.5 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0213] Example 4-2

[0214] In the preparation step of the composition for a microporous layer, 67.66 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.34 g of La-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 10; La 0.7 at%) (0.5 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1.

[0215] Example 4-3

[0216] In the preparation step of the composition for a microporous layer, 67.66 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.34 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 5; N 0.8 at%) (0.5 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1.

[0217] Example 4-4

[0218] In the preparation step of the composition for a microporous layer, 67.66 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.34 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 7; N 1.0 at%) (0.5 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1.

[0219] Example 5

[0220] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of cube-shaped cerium oxide (CeO2) particles (Preparation Example 2) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1.

[0221] Example 5-1

[0222] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 7; N 1.0 at%) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0223] Example 5-2

[0224] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of nitrogen-doped cube-shaped cerium oxide (CeO2) particles (separate preparation example: N 1.4 at%) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0225] Example 5-3

[0226] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of La-doped cube-shaped cerium oxide (CeO2) particles (Preparation Example 10; La 0.7 at%) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1.

[0227] Example 5-4

[0228] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of La-doped cube-shaped cerium oxide (CeO2) particles (separate preparation example; La 1.2 at%) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1, except that the mixture was mixed.

[0229] Example 6

[0230] In the preparation step of the composition for a microporous layer, 65.96 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 2.04 g of cube-shaped cerium oxide (CeO2) particles (Preparation Example 2) (3.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1.

[0231] Example 7

[0232] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of rod-shaped cerium oxide (CeO2) particles (Preparation Example 1) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was manufactured in the same manner as in Comparative Example 1.

[0233] Example 8

[0234] In the preparation step of the composition for a microporous layer, 67.32 g of the conductive carbon particles, 53.4 g of the PTFE emulsion (solid content 32 g) were mixed, and 0.68 g of octahedral cerium oxide (CeO2) particles (Preparation Example 3) (1.0 wt% relative to the weight of the conductive carbon particles) were mixed, and a GDL was prepared in the same manner as in Comparative Example 1.

[0235] Table 7 below summarizes the material composition of the microporous layer of the GDL manufactured in the comparative examples and examples above.

[0236] MPL Main Material Composition Conductive Carbon Particles Water Repellent Binder Resin Radical Scavenger CeO2 Content Compared to Conductive Carbon Particles CeO2 Doped Nitrogen (N) CeO2 Doped La Particle Structure ggg Weight % Atomic % Atomic % Example 167.99 320.01 0.01--Cube Example 1-10.7-Example 1-20.8-Example 267.97 320.03 0.04--Cube Example 367.93 320.07 0.1--Cube Example 467.66 320.34 0.5--Cube Example 4-10.7-Example 4-2-0.7 Example 4-30.8-Example 4-41.0-Example 567.32320.681.0--Cube Example 5-11.0--Example 5-21.4--Example 5-3-0.7 Example 5-4-1.2 Example 665.96322.043.0--Example 767.32320.681.0--Rod Example 867.32320.681.0--Octahedron Comparative Example 168.003200.0--Spherical Comparative Example 267.32320.681.0--Example 365.96322.043.0--Example 463.24324.767.5--

[0237] Manufacturing example: Manufacturing of a fuel cell unit cell

[0238] A unit cell of a polymer electrolyte fuel cell was manufactured by laminating gas diffusion layers according to each of the above-described examples and comparative examples as cathode gas diffusion layers and anode gas diffusion layers on both sides of a commercial polymer electrolyte membrane (purchased from Gore Ltd., product name: Primeas 5730) having a catalyst layer applied to both surfaces.

[0239] [Evaluation Example: Electrical Resistance Measurement]

[0240] The manufactured gas diffusion layer was cut into six pieces using a circular cutter with a diameter of 24 mm to manufacture measurement specimens. Four measurement specimens were inserted between gold-plated copper plates, and a pressure of 425 N was applied, and a force of 4.52 A (1.0 A / cm) was applied in the thickness direction. 2) was passed through the sample and the resulting voltage drop (V) was measured. After removing the measured specimen, two specimens were inserted between gold-plated copper plates and the voltage drop (V) was measured using the same method. The resistance value (unit: mΩㆍcm) was calculated from the difference between the two resistances. 2 ) was calculated.

[0241] Electrical resistance value (unit: mΩㆍcm) 2 ) = (Voltage of 4 gas diffusion layers - Voltage of 2 gas diffusion layers) / 2.

[0242] [Evaluation example: Air permeability]

[0243] The air permeability of the manufactured gas diffusion layer was measured using an air permeability tester (model: FX3300-IV, manufacturer: Textest Instuments, France). At this time, the air permeability was measured at room temperature (approximately 20℃), and the measurement area was set to 38㎠. The air permeability (㎤ / ㎠ㆍs) was measured when the differential pressure of the air sucked through the gas diffusion layer by the air permeability tester was 200Pa.

[0244] [Evaluation Example: Contact Angle Measurement]

[0245] Changes in the contact angle value of the gas diffusion layer were measured in sessile drop mode using a contact angle measurement system (model name: DSA10, manufacturer: KRUSS GmbH). That is, distilled water was filled into a microsyringe, 9 μl of distilled water was allowed to accumulate in the syringe, and this was settled on the MPL surface of the gas diffusion layer to measure the size of the contact angle. The measurement temperature was maintained at 20 ± 5 °C.

[0246] Table 8 below summarizes the properties obtained from the comparative examples and examples described above.

[0247] Gas diffusion layer properties Electrical resistance MPL Contact angle Air permeability @ 200 PamΩㆍcm2°cm3 / cm2ㆍsec Example 15.72±0.08 157±1.2 0.21±0.03 Example 1-15.71±0.05 157±0.9 0.20±0.02 Example 1-25.71±0.06 156±1.1 0.21±0.01 Example 25.71±0.10 157±0.8 0.22±0.03 Example 35.73±0.09 155±0.9 0.23±0.04 Example 45.87±0.14 153±1.2 0.25±0.03 Example 4-15.85±0.12152±2.10.26±0.02Example 4-25.84±0.08153±1.70.25±0.04Example 4-35.82±0.12151±1.90.27±0.01Example 4-45.84±0.07151±2.30.24±0.02Example 56.03±0.12151±0.70.30±0.05Example 5-16.01±0.09150±1.10.29±0.04Example 5-26.08±0.18151±1.40.27±0.06Example 5-36.05±0.07152±0.90.28±0.03Example 5-46.03±0.07151±2.10.29±0.02Example 66.22±0.06150±1.70.31±0.04Example 76.21±0.08150±1.90.32±0.03Example 86.17±0.16151±2.80.31±0.04Comparative Example 15.51±0.17157±2.30.21±0.02Comparative Example 25.57±0.19157±4.10.22±0.02Comparative Example 36.23±0.11155±3.70.25±0.05Comparative Example 47.41±0.34152±4.80.30±0.05

[0248] Referring to Table 8, it can be confirmed that the conventional commercial cerium oxide radical trapping agent has insufficient free radical trapping activity, so when the amount used is increased to ensure sufficient radical trapping performance (Comparative Example 2-4), the electrical resistance increases due to its nonconductive and hydrophilic properties and the hydrophilicity increases (contact angle decreases), which suppresses water discharge in the high current density operation area during high current density operation, thereby causing water flooding.

[0249] Compared to Comparative Example 1, which consists only of conductive carbon particles and a water-repellent resin, it can be confirmed that as the content of the radical trapping agent increases, regardless of whether it is a spherical radical trapping agent or a structure-controlled radical trapping agent, the electrical resistance of the gas diffusion layer increases due to the radical trapping agent having low conductivity. In addition, as the content of the radical trapping agent, which is a metal oxide, increases, the contact angle decreases as the water adsorption capacity on the surface of the microporous layer increases. The water-repellent binder of the microporous layer not only functions as a water-repellent agent of the microporous layer but also functions as a binder for the conductive particles and the radical trapping agent. In the case of the size-controlled radical trapping agent, since the particle sizes are different from those of the spherical radical trapping agent, the binder requirement increases somewhat, resulting in a smaller contact angle on the surface of the microporous layer. This increases the size of the pores that can be created between particles with different sizes, which tends to slightly increase the gas permeability.

[0250] [In situ durability evaluation]

[0251] (1) Activation

[0252] The unit cell temperature was adjusted to 65℃ and the relative humidity of the anode and cathode was 100%. Hydrogen and air were supplied to the anode and cathode at a flow rate of 1.0 L / min and 3.0 L / min, respectively, and the unit cell was maintained at the open circuit potential (OCV) for 1 minute. Then, the potential was decreased by 0.1 V from 0.9 V to 0.4 V, and maintained at each potential for 10 seconds. After that, it was maintained at 0.4 V for 5 minutes, and then increased by 0.1 V again to 0.9 V, and maintained at each potential for 10 seconds, and then maintained at OCV for 1 minute. The above process was defined as one cycle. This process was repeated 30 cycles to activate the unit cell.

[0253] (2) Initial performance evaluation at 100% relative humidity

[0254] In the activated unit cell, hydrogen and air were supplied at 0.114 L / min and 0.362 L / min, respectively, up to a current section of 10 A, and the current was increased by 2.5 A and maintained at each current for 1 minute. The average voltage of the unit cell for the last 30 seconds was measured. In the current section above 10 A, the stoichiometric ratios of hydrogen and air were set to 1.5 and 2.0, respectively.

[0255] The current density at 0.6 V and the voltage value of the unit cell at 2.0 A / cm2 were used as indicators to evaluate the electrical performance of the unit cell.

[0256] (3) Electrical corrosion

[0257] The temperature of the unit cell, for which the initial performance evaluation was completed, was adjusted to 65℃, and the anode and cathode were in an environment with 100% relative humidity. While hydrogen and nitrogen were supplied to the anode and cathode at a flow rate of 0.2 L / min, respectively, a loader was connected to the anode and cathode, and voltage pulses of 1.0 V and 1.5 V were alternately applied for 1 second each. When the voltage application time for 1.0 second at each of the above voltages, i.e., the total voltage application time of 2 seconds, is defined as one cycle, 1,200 cycles were repeated to induce corrosion in the unit cell. This repetitive voltage application causes corrosion of the catalyst support in the catalyst layer, and further corrodes the carbon particles in the microporous layer adjacent to the catalyst layer.

[0258] (4) Single cell performance evaluation of corroded polymer electrolyte membrane (including catalyst layer) and gas diffusion layer

[0259] After 1,200 cycles of pulse voltage application were completed, the temperature of the unit cell was adjusted to 65°C, and the anode and cathode were readjusted so that they were in an environment with 100% relative humidity. Thereafter, the performance of the unit cell was evaluated under the method and conditions described in (2) above. At this time, the performance of the unit cell was evaluated in a state where both the polymer electrolyte membrane (including the catalyst layer) and the gas diffusion layer were corroded.

[0260] (5) Performance evaluation of unit cell after replacement of polymer electrolyte membrane (including catalyst layer)

[0261] After the performance evaluation is completed, nitrogen gas is supplied to both the anode and cathode of the unit cell, and the temperature of the unit cell is cooled to room temperature. The nitrogen gas supply to the cooled unit cell is cut off and it is separated from the evaluation equipment. The polymer electrolyte membrane (including the catalyst layer) from the unit cell is discarded and replaced with a new commercial polymer electrolyte membrane (including the catalyst layer), and the corroded anode gas diffusion layer and cathode gas diffusion layer are reused to reassemble the unit cell. Thereafter, the performance of the unit cell is evaluated under the method and conditions described in (2) above. From this test, the degree of performance decline due to corrosion of the gas diffusion layer can be confirmed.

[0262] (6) Comparison of unit cell performance through corrosion evaluation of gas diffusion layer

[0263] From the unit cell performance evaluation of the gas diffusion layer, three types of current-voltage curves (IV curves) shown in Fig. 15 can be obtained.

[0264] i) Initial performance: Current-voltage curve performance (solid line) of a fuel cell with both a fresh polymer electrolyte membrane (including the catalyst layer) and a gas diffusion layer.

[0265] ii) Current-voltage curve performance (dotted line) of a fuel cell with both the polymer electrolyte membrane (including the catalyst layer) and the gas diffusion layer and the gas diffusion layer corroded after 1,200 cycles of 1.0 V / 1.5 V pulse voltage application.

[0266] iii) Current-voltage curve performance of a unit cell including a corroded gas diffusion layer after replacement of the catalyst layer and polymer electrolyte membrane (dot-dashed line)

[0267] (7) Unit battery cell performance reduction rate evaluation (durability evaluation)

[0268] To evaluate the performance degradation of the gas diffusion layer due to carbon particle corrosion in the microporous layer generated by applying 1,200 cycles of 1.0 V / 1.5 V pulse voltage, the output current density at 0.6 V was compared. The performance degradation rate is calculated using the following formula.

[0269] Performance decline rate = [(Initial current density at 0.6 V - Current density at 0.6 V after replacement of catalyst layer and polymer electrolyte membrane) / (Initial current density at 0.6 V)] × 100(%).

[0270] Unit cell performance evaluation Initial performance Performance after 1,200 cycles of 1.0 V / 1.5 V pulse voltage application, after replacement of polymer electrolyte membrane (including catalyst layer) Current density at 0.6 V Voltage at 2.0 A / cm2 Current density at 0.6 V Voltage at 2.0 A / cm2 Performance reduction rate @ 0.6 VA / cm2 VA / cm2 V% Example 11.60 10.5 5 1.5 2 7 0.5 4 7 4.62% Example 1-11.60 00.5 5 1.5 2 7 0.5 4 6 4.56% Example 1-21.60 20.5 5 6 1.5 3 0 0.5 4 8 4.49% Example 21.60 20.5 5 4 1.5 3 0 0.5 4 7 4.51% Example 31.60 10.55 51.53 10.54 64.36% Example 41.60 30.55 31.53 60.54 34.21% Example 4-11.60 50.55 41.54 40.54 63.82% Example 4-21.60 70.55 31.54 80.54 53.69% Example 4-31.60 50.55 31.54 60.54 13.67% Example 4-41.60 40.55 31.54 80.54 33.49% Example 51.60 10.55 11.55 20.53 53.05% Example 5-11.5980.5521.5500.5373.03%Example 5-21.6030.5511.5550.5372.98%Example 5-31.6040.5521.5550.5373.04%Example 5-41.6050.5511.5570.5363.01%Example 61.5990.5481.5070.5155.72%Example 71.6020.5511.5460.5373.49%Example 81.6030.5501.5360.5364.21%Comparative Example 11.5970.5551.4270.53210.40%Comparative Example 21.6030.5551.5240.5434.93%Comparative Example 31.5840.5511.5360.5323.03%Comparative Example 41.5710.5431.4590.5177.13%

[0271] From the results summarized in Table 9, it can be confirmed that the fuel cell assembled using a gas diffusion layer including a cerium oxide particle radical trapping agent having a controlled shape in a microporous layer according to the present disclosure exhibits excellent unit cell initial performance, prevention of performance degradation in a high current density operation range, and excellent unit cell durability comparable to the case where a large amount of commercially available spherical cerium oxide particle radical trapping agent is used, even when a small amount of the cerium oxide particle radical trapping agent having a controlled shape is used. This is because the radical removal performance of the cerium oxide particle radical trapping agent having a controlled shape is improved, so that sufficient radical removal performance can be exhibited even when only a small amount is used compared to the amount of commercially available spherical cerium oxide particle radical trapping agent, and performance degradation due to water flooding can be effectively suppressed in a high current density operation range.

[0272] The description of this disclosure is essentially illustrative only, and therefore, modifications that do not depart from the essence of this disclosure are intended to be within the scope of this disclosure. Such modifications should not be deemed to depart from the spirit and scope of this disclosure.

[0273] The present invention relates to a gas diffusion layer for manufacturing a fuel cell and a fuel cell employing the same.

Claims

1. As a gas diffusion layer for fuel cells, The above gas diffusion layer includes a carbon substrate and a microporous layer formed on the carbon substrate, The microporous layer comprises carbon particles and a water-repellent resin binding the carbon particles, and the microporous layer further comprises a radical scavenger selected from cerium oxide particles having a controlled particle shape. A gas diffusion layer wherein the controlled particle shape is at least one selected from a cuboid, a cube, an octahedron, or a polyhedron having nine or more surfaces, and the cerium oxide particles include nano-sized cerium oxide particles doped with a non-metallic element and / or a metal element.

2. In the first paragraph, the microporous layer contains 15 to 45 wt% of the water-repellent resin and 55 to 85 wt% of the carbon particles, A gas diffusion layer, wherein the content of cerium oxide particles having the controlled particle shape among the microporous layer is 0.01 wt% or more and 3.0 wt% or less relative to the weight of the carbon particles.

3. A gas diffusion layer in the first aspect, wherein the nano-sized cerium oxide particles have a size of less than 100 nm, 15 nm to 70 nm, 18 nm to 60 nm, 18 nm to 50 nm, 25 nm to 50 nm, 30 nm to 45 nm, 35 nm to 44 nm, 36 nm to 44 nm, 38 nm to 44 nm, 40 nm to 44 nm, or 41 nm to 43 nm.

4. A gas diffusion layer in the first paragraph, wherein the doped non-metallic element is at least one selected from nitrogen, phosphorus, sulfur, chlorine, and fluorine; and the doped non-metallic element is at least one selected from La, Pr, Sm, Eu, Gd, Y, Zr, and Nb.

5. In the fourth paragraph, the doping amount of the non-metallic element is 0.1 to 3.0 at%, 0.2 to 3.0 at%, 0.3 to 3.0 at%, 0.4 to 3.0 at%, 0.5 to 2.5 at%, 0.6 to 2.0 at%, 0.7 to 1.5 at%, 0.8 to 1.3 at%, 0.8 to 1.2 at%, 0.8 to 1.1 at%, 0.8 to 1.0 at%, 0.9 to 1.4 at%, 1.0 to 1.3 at%, 1.1 to 1.4 at%, or 1.2 to 1.3 at%, based on the doped cerium oxide particle sample.

6. In the fourth paragraph, the doping amount of the metal element is 0.1 to 3.0 at%, 0.2 to 3.0 at%, 0.3 to 3.0 at%, 0.4 to 3.0 at%, 0.2 to 2.5 at%, 0.3 to 2.0 at%, 0.4 to less than 1.5 at%, 0.5 to 1.4 at%, 0.6 to 1.3 at%, 0.7 to 1.2 at%, 0.7 to 1.1 at%, 0.7 to 1.0 at%, 0.8 to 1.2 at%, 0.8 to 1.1 at%, 0.8 to 1.0 at% or 0.8 to 1.0 at% based on the doped cerium oxide particle sample.

7. In the first paragraph, the cerium oxide particles are Ce 3+ Ion and Ce 4+ Ce ions are included, and Ce is present in the cerium oxide particles and / or the doped cerium oxide particles. 3+ Ion and Ce 4+ Ce of ion 3+ : Ce 4+ A gas diffusion layer comprising cerium oxide having a molar ratio of 0.2:0.8 to 0.8:0.2, wherein the molar ratio is a value obtained by deconvolution of peaks at the Ce 3d binding energy level on an X-ray photoelectron spectroscopy spectrum.

8. A gas diffusion layer characterized in that in the first paragraph, the water-repellent resin is a fluorinated resin and is included in both the carbon substrate and the microporous layer.

9. A gas diffusion layer in the first paragraph, wherein the carbon particles include at least one selected from carbon black, activated carbon, carbon black, acetylene black, Ketjen black, Denka black, carbon whiskers, activated carbon fibers, vapor grown carbon fibers (VGCF), carbon aerosol, carbon nanotubes, carbon nanofibers, carbon nanohorns, and graphite.

10. A membrane electrode assembly for a fuel cell comprising a gas diffusion layer according to any one of claims 1 to 9.

11. A fuel cell comprising a membrane electrode assembly according to paragraph 10.

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