Antioxidant for fuel cell, membrane electrode assembly including the same, and method for preparing the antioxidant

Abstract

The present invention discloses an antioxidant for a fuel cell, a membrane electrode assembly thereof and a method for preparing the antioxidant. The antioxidant for a fuel cell comprises a core and an outer portion (e.g., a shell), wherein the core comprises a metal oxide (M x O k ) and composite metal oxides (M x N y O j , N and M are different metals), the outer portion is located on or above the surface of the core and is formed by reducing the surface of the core using a thiourea-based compound. The outer portion includes a metal cation (M (x‑n)+ , n is a natural number of 1 or greater), the metal cation has an oxidation number smaller than the valence of the core metal (M).

Description

Technical Field

[0001] The present invention relates to an antioxidant for a fuel cell, a membrane electrode assembly comprising the antioxidant and a method for preparing the antioxidant. Background Art

[0002] Typically, hydrogen and oxygen in the air used as fuel cell reaction gases pass through the electrolyte membrane, thereby promoting the generation of hydrogen peroxide (HOOH). Such hydrogen peroxide can generate highly reactive oxygen-containing free radicals, such as hydroxyl radicals (·OH) and hydroperoxyl radicals (·OOH). These free radicals attack the ionomers of the electrolyte membrane and electrodes based on perfluorosulfonic acid, thus potentially causing degradation of the electrolyte membrane and electrodes, thereby reducing the durability of the fuel cell.

[0003] As a technique to mitigate the chemical degradation of conventional electrolyte membranes and electrodes, methods of adding various antioxidants have been proposed. These antioxidants can be divided into primary antioxidants used as free radical scavengers or quenchers and secondary antioxidants used as hydrogen peroxide decomposers. In addition, the primary antioxidant and the secondary antioxidant can be used alone or in combination.

[0004] The electrolyte membrane to which an excessive amount of antioxidant is added has increased chemical durability, but the sulfonated groups in the electrolyte membrane still bind to the cationic antioxidant to reduce hydrophilicity, thereby reducing proton conductivity and possibly causing reduced performance of the fuel cell. Therefore, it is necessary to use antioxidants appropriately in consideration of performance and durability.

[0005] In the prior art, cerium oxide-based antioxidants can be introduced in the form of nanopowders with a particle size of several nanometers or tens of nanometers, and cerium oxide-based antioxidants are usually stored in an agglomerated state after preparation, so they need to be dispersed before being added to the electrolyte membrane. For example, a mechanical dispersion method (such as a bead milling dispersion method or an ultrasonic dispersion method) and a chemical dispersion method using a surfactant can be used.

[0006] One of the main properties of antioxidants is to quickly stabilize free radicals. For example, in order to have a high antioxidant capacity, when a cerium oxide-based antioxidant has a large particle surface area and a high proportion (i.e., content) of trivalent cerium cations (Ce 3+ ), the cerium oxide-based antioxidant exhibits excellent hydroxyl radical stability through the following reaction formula 1.

[0007] [Reaction formula 1]

[0008] Ce 3+ +·OH+H + →Ce 4+ +H 2 O

[0009] For this purpose, antioxidants with larger surface areas can be introduced, but such antioxidants are easily agglomerated by van der Waals forces. In addition, antioxidants can be dissolved in the process of manufacturing electrolyte membranes under acidic atmospheres, so cerium cations can be discharged to the outside of the fuel cell. In addition, such antioxidants may poison the cathode, thereby reducing the performance and durability of the fuel cell. Therefore, it is necessary to develop antioxidants with high antioxidant capacity and a particle size that ensures dissolution stability.

[0010] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Summary of the invention

[0011] In a preferred aspect, an antioxidant is provided, which is formed after surface treatment with a reducing agent, such as a thiourea-based compound.

[0012] Furthermore, the present invention provides an antioxidant having an enhanced antioxidant ability by subjecting a metal on the surface of the antioxidant to a reduction treatment.

[0013] Furthermore, the present invention provides an antioxidant having a particle size that ensures dissolution stability and enhanced antioxidant ability, thereby increasing the performance and durability of a membrane electrode assembly or a fuel cell including the antioxidant.

[0014] In one aspect, an antioxidant for a fuel cell is provided. The antioxidant may include a core and an outer portion (e.g., a shell), wherein the core includes a metal oxide (M x O k ) and composite metal oxides (M x N y O j , N and M are different metals), the outer portion is located on the surface or above the core and includes a metal cation (M (x-n)+ , n is a natural number of 1 or greater), the metal cation has an oxidation number less than the valence of the core metal (M). Preferably, the outer portion (e.g., shell) can be formed by performing a reduction treatment on the surface of the core using a reducing agent. For example, the reducing agent may include a thiourea-based compound, and exemplary reducing agents may appropriately include thiourea (NH 2 CSNH 2 ), thiourea dioxide (NH 2 C(=NH)SO 2 H), 1,3-diisopropyl-2-thiourea ((CH 3 ) 2 CHNHCSNHCH(CH 3 ) 2)、1-(2-methoxyphenyl)-2-thiourea (CH 3 OC 6 H 4 NHCSNH 2 ), propylene thiourea (C 4 H 8 N 2 S) and 1-(2-furfuryl)-2-thiourea (C 6 H 8 N 2 O s )

[0015] Preferably, the metal (M) may suitably include cerium (Ce), and the core may include a tetravalent cerium cation (Ce 4+ ) and the outer portion (shell) may include a compound having a trivalent cerium cation (Ce 3+ ) compounds.

[0016] Preferably, the composite metal oxide may appropriately include one or more selected from the group consisting of cerium zirconium oxide, gadolinium-doped cerium oxide, samarium-doped cerium oxide, titanium dioxide-supported cerium oxide, and silicon dioxide-supported cerium oxide.

[0017] The crystal size of each of the metal oxide and the composite metal oxide measured by X-ray diffraction (XRD) or Brunauer-Emmett-Teller (BET) method may be about 5 nm to 100 nm.

[0018] Preferably, the antioxidant may form agglomerated particles having a size of about 10 nm to 500 nm.

[0019] In another preferred embodiment, the core may include a tetravalent cerium cation (Ce 4+ ) of cerium oxide (CeO 2 ), and the outer portion (e.g., shell) includes a trivalent cerium cation (Ce 3+ ) 2 O 3 The metal in the exterior can be reacted by, for example, using thiourea (NH 2 CSNH 2 ) is formed by performing a reduction treatment on the surface of the core.

[0020] [Reaction 2]

[0021] 2[CS(NH 2 ) 2 ]+2CeO 2 +H 2 O→[(NH 2 ) 2CSSC(NH) 2 ](OH) 2 +Ce 2 O 3 .

[0022] In another aspect, a membrane electrode assembly is provided, the membrane electrode assembly including an electrolyte membrane and electrodes formed on both surfaces of the electrolyte membrane. In particular, at least one of the electrolyte membrane or the electrodes may include the above antioxidant.

[0023] In another aspect, a method for preparing an antioxidant for a fuel cell is provided. The method may include: preparing a first blend, the first blend including: i) a metal component, the metal component including a metal oxide (M x O k ) and composite metal oxides (M x N y O j , N and M are different metals), and ii) deionized (DI) water; preparing a dispersion by dispersing the first blend; preparing a second blend by the dispersion and a reducing agent; subjecting the metal component to a reduction treatment on its surface; and drying the second blend to obtain an antioxidant.

[0024] The antioxidant may have a core including a metal component and an outer portion (eg, a shell) including a metal cation (M (x-n)+ , n is a natural number of 1 or greater), the metal cation has an oxidation number less than the metal oxide (M x O k ) and composite metal oxides (M x N y O j ) The valence of each metal (M). In particular, the outer portion may be formed on the reduction-treated surface of the antioxidant.

[0025] Preferably, the reducing agent may include a thiourea-based compound. The thiourea-based compound may suitably include a compound selected from thiourea (NH 2 CSNH 2 ), thiourea dioxide (NH 2 C(=NH)SO 2 H), 1,3-diisopropyl-2-thiourea ((CH 3 ) 2 CHNHCSNHCH(CH 3 ) 2 )、1-(2-methoxyphenyl)-2-thiourea (CH 3 OC 6 H 4 NHCSNH 2), propylene thiourea (C 4 H 8 N 2 S) and 1-(2-furfuryl)-2-thiourea (C 6 H 8 N 2 O s )

[0026] The term "surface treatment" may include reduction, reduction reaction, the step of reduction treatment for changing (e.g., reducing) the valence of the metal on the core surface. In certain embodiments, surface treatment refers to the following chemical reaction, i.e., by using a reducing agent or reducing agent to reduce the valence of the metal on the core surface, thereby forming an outer portion (e.g., shell) around at least part of the core and the metal of the outer portion or shell has a valence different from (i.e., reducing or less than) the metal in the core. In certain embodiments, "surface treatment" can be used interchangeably with "reduction treatment" or "reduction treatment".

[0027] Preparing the dispersion can include combining the first admixture with an ionomer dispersion having a pH above about 2.5.

[0028] Preferably, preparing the dispersion may comprise using a nano-disperser. As used herein, the term "nano-disperser" refers to a device that performs dispersion.

[0029] Preferably, preparing the second admixture may be performed at a pH ranging from about 5 to 11.

[0030] Preferably, the preparation of the second admixture may be carried out at a temperature in the range of about 10°C to 80°C. Preferably, the metal component comprises cerium oxide (CeO 2 ), and in the reduction treatment, the reaction shown in the following reaction formula 2 may occur,

[0031] [Reaction 2]

[0032] 2[NH 2 CSNH 2 ]+2CeO 2 +H 2 O→[(NH 2 ) 2 CSSC(NH) 2 ](OH) 2 +Ce 2 O 3 .

[0033] The method may further include preparing a reducing agent by mixing a thiourea-based compound, deionized (DI) water, and a pH adjuster before preparing the second admixture.

[0034] Preferably, hydrogen peroxide (H2O2) may be used before the reduction treatment. 2 O 2 ) The reducing agent is pretreated. For example, the reducing agent is pretreated by the reaction shown in Formula 4-1:

[0035] [Reaction 4-1]

[0036] (NH 2 ) 2 CSO 2 H+2OH - →(NH 2 ) 2 CO+HSO 2 - .

[0037] Preferably, the reduction treatment is performed by using the reaction product of Formula 4-1 as a reactant in the reaction shown in Formula 4-2,

[0038] [Reaction 4-2]

[0039] 2HSO 2 - +2CeO 2 →2SO 2 +Ce 2 O 3 +H 2 O.

[0040] Other aspects of the invention are discussed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order that the present disclosure may be better understood, various forms thereof will now be described by way of example with reference to the accompanying drawings, in which:

[0042] Figure 1 Schematically illustrating an antioxidant for a fuel cell according to an exemplary embodiment of the present invention;

[0043] Figure 2A and Figure 2B Exemplary thiourea-based compounds suitable for use in several embodiments of the present invention are shown;

[0044] Figure 3 is a graph comparatively showing characteristics of exemplary antioxidants according to an exemplary embodiment of the present invention;

[0045] Figure 4 is a flow chart illustrating an exemplary method of preparing an exemplary antioxidant for a fuel cell according to various exemplary embodiments of the present invention;

[0046] Figure 5 Showing the results of Evaluation Example 1 according to an exemplary embodiment of the present invention;

[0047] Figure 6 shows the results of Evaluation Example 2 according to an exemplary embodiment of the present invention; and

[0048] Figure 7 The results of Evaluation Example 3 according to the exemplary embodiment of the present invention are shown.

[0049] It should be understood that the accompanying drawings are not necessarily to scale and are slightly simplified representations of various preferred features illustrative of the basic principles of the present invention. The specific design features of the present invention disclosed herein, including, for example, specific size, orientation, location and shape, will be determined in part by the application and use environment of the specific purpose.

[0050] In the figures, reference numbers refer to the same or equivalent parts throughout the several figures of the drawing.

[0051] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. DETAILED DESCRIPTION

[0052] Various embodiments of the present invention will be mentioned in detail below, examples of which are illustrated in the accompanying drawings and described below. Although the present invention is described in conjunction with exemplary embodiments, it should be understood that this specification is not intended to limit the present invention to those exemplary embodiments. On the contrary, the present invention is intended to cover not only these exemplary embodiments, but also various replacements, modifications, equivalents and other embodiments within the spirit and scope of the present invention as defined by the appended claims. In the following description of the embodiments, even if the same elements are shown in different drawings, they are represented by the same reference numerals.

[0053] Unless stated as having other definitions, all terms (including technical terms and scientific terms) used in the following description of the embodiment are interpreted as having meanings that can be understood by those skilled in the art. In addition, unless clearly defined to have special meanings, terms defined in commonly used dictionaries should not be interpreted ideally or excessively.

[0054] In addition, the terms used in the description of the embodiment are only used for the embodiment described and do not limit the present invention. In the description of the embodiment, singular expressions may include plural expressions unless they have significantly different contextual meanings. In the following description of the embodiment, terms such as "comprising", "including", "having" are interpreted as indicating the existence of features, numbers, steps, operations, elements and / or parts or combinations thereof described in the description, and do not exclude the possibility of having one or more other features, numbers, steps, operations, elements and / or parts, combinations thereof or adding them. In addition, the term "and / or" is interpreted as including all combinations of each stated item and one or more thereof.

[0055] In addition, it will be understood that when a component such as a layer, film, region, or panel is referred to as being "on" another component, the component may be "directly" on the other component, or other components may be interposed between the two components. In the same manner, it will be understood that when a component such as a layer, film, region, or panel is referred to as being "under" another component, the component may be "directly" under the other component, or other components may be interposed between the two components.

[0056] All numbers, values ​​and / or expressions used in the specification to represent the amount of components, reaction conditions, polymer compositions and blends are approximate values, which reflect the various uncertainties in the measurements generated when these values ​​are obtained from essentially different things, so unless otherwise stated, they should be understood to be modified by the term "about". For example, "about" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% or 0.01% of the value. Unless the context clearly indicates, all numerical values ​​provided herein are modified by the term "about".

[0057] In addition, it will be understood that if a numerical range is disclosed in the specification, unless otherwise stated, the range includes all continuous values ​​from the minimum value to the maximum value of the range. In addition, if such a range refers to an integer, unless otherwise stated, the range includes all integers from the minimum integer to the maximum integer.

[0058] In the following description of the embodiments, it will be understood that when stating a range for a variable, the variable includes all values ​​within the range, including the endpoints of the range. For example, it will be understood that the range of "5 to 10" includes not only the values ​​of 5, 6, 7, 8, 9, and 10, but also any subranges, such as a subrange of 6 to 10, a subrange of 7 to 10, a subrange of 6 to 9, a subrange of 7 to 9, etc., and any value between the valid integers within the range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. In addition, for example, it will be understood that the range of "10% to 30%" includes not only all integers including the values ​​of 10%, 11%, 12%, 13%,...30%, but also includes any sub-ranges, such as a sub-range of 10% to 15%, a sub-range of 12% to 18%, a sub-range of 20% to 30%, etc., as well as any value between the valid integers in the said range, such as 10.5%, 15.5%, 25.5%, etc.

[0059] The present invention will be described in detail below with reference to the accompanying drawings.

[0060] In one aspect, an antioxidant for a fuel cell is provided. The antioxidant may include i) a core, the core comprising a metal oxide (M x O k ) and composite metal oxides (M x N y O j , N and M are different metals) one or more; and ii) an outer portion or shell, the outer portion or shell is located on the surface of the core or above and includes a metal cation (M (x -n)+ , n is a natural number of 1 or greater), the metal cation has an oxidation number less than the valence of the core metal (M). The metal component in the core refers to one or more of metal oxides and composite metal oxides that can be used interchangeably.

[0061] Figure 1 An exemplary antioxidant for a fuel cell according to an exemplary embodiment of the present invention is schematically shown.

[0062] like Figure 1 As shown, the antioxidant for a fuel cell may include a core 100 and an outer shell 200, wherein the core 100 includes a metal oxide (M x O k ) and composite metal oxides (M x N y O j, N and M are different metals), the outer shell 200 is located on the surface of the core 100. In particular, the outer shell can be formed by reducing the surface of the core 100 using a reducing agent. The reducing agent can appropriately include a thiourea-based compound. In particular, the outer shell 200 may include a metal cation ((M (x-n)+ , n is a natural number of 1 or greater), the metal cation has an oxidation number smaller than the valence of the metal M included in the core 100.

[0063] The composite metal oxide included in the core 100 may include one or more selected from cerium zirconium oxide, gadolinium-doped cerium oxide, samarium-doped cerium oxide, titanium dioxide-supported cerium oxide, and silicon dioxide-supported cerium oxide, but is not limited thereto, and therefore, various metal oxides and composite metal oxides other than metal salt hydrates may be used. Preferably, in order to obtain the most excellent antioxidant ability, the metal M may include cerium (Ce), manganese (Mn), or a combination thereof.

[0064] The crystal size of the metal oxide or composite metal oxide measured by, for example, X-ray diffraction (XRD) or Brunauer-Emmett-Teller (BET) method may be about 5 nm to 100 nm. In particular, the metal oxide or composite metal oxide may include cerium (Ce), that is, cerium oxide or composite cerium oxide may be used, and the crystal size of the cerium oxide or composite cerium oxide measured by X-ray diffraction (XRD) or Brunauer-Emmett-Teller (BET) method may be about 5 nm to 100 nm.

[0065] The particle size that the antioxidant for fuel cell according to various exemplary embodiments of the present invention obtains by agglomeration can be about 10nm to 500nm.Such particle size can represent the size of agglomerated particles formed by attraction between antioxidant particles.When the particle size of antioxidant is several nanometers (nm), the antioxidant may have high antioxidant capacity due to large surface area, and also has high solubility.Preferably, the antioxidant can have an agglomerated particle size of about 10nm or larger, thereby having dissolution stability and excellent antioxidant capacity.

[0066] In the metal oxide or composite metal oxide included in the antioxidant according to various exemplary embodiments of the present invention, the metal M may include, for example, cerium (Ce). In particular, cerium oxide (Ce x O k ) can be used as metal oxides.

[0067] like Figure 1As shown, the surface treated antioxidant core 100 may include a tetravalent cerium cation (Ce 4+ ) compounds, and the outer (shell) 200 of the surface-treated antioxidant may include a trivalent cerium cation (Ce 3+ The outer shell 200 may include a trivalent cerium cation (Ce 3+ ), which is composed of a tetravalent cerium cation (Ce 4+ ) is reduced to have a higher 4+ )'s oxidation number decreases by 1.

[0068] Therefore, the antioxidant according to the exemplary embodiment of the present invention can quickly stabilize the free radical (·OH) and have an increased antioxidant capacity. 3+ ) increases, the reaction of the above reaction formula 1 increases, and therefore, the antioxidant can have a higher hydroxyl radical stabilizing ability and a higher antioxidant capacity.

[0069] When the surface of the core 100 of the antioxidant is treated to form the outer shell 200, the thiourea-based compound may be used as a reducing agent or reducing agent. The thiourea-based compound may basically include carbon (C), an amine group (-NH 2 ) or amino (-NH-) (including nitrogen) and sulfur (S).

[0070] For example, the thiourea-based compound may include a thiourea (NH 2 CSNH 2 ), thiourea dioxide (NH 2 C(=NH)SO 2 H), 1,3-diisopropyl-2-thiourea ((CH 3 ) 2 CHNHCSNHCH(CH 3 ) 2 )、1-(2-methoxyphenyl)-2-thiourea (CH 3 OC 6 H 4 NHCSNH 2 ), propylene thiourea (C 4 H 8 N 2 S) and 1-(2-furfuryl)-2-thiourea (C 6 H 8 N 2 O s ) in one or more. However, it is not excluded to increase the trivalent cerium cation (Ce3+ ) ratio of other types of thiourea-based compounds.

[0071] In the following, reference will be made to Figure 2A and Figure 2B The reducibility of the thiourea-based compound is described in more detail by way of example.

[0072] Figure 2A Thiourea (NH 2 CSNH 2 )'s molecular structure, Figure 2B Thiourea dioxide (NH 2 C(=NH)SO 2 H). Figure 2A and Figure 2B The two thiourea-based compounds shown are organic compounds including carbon (C), nitrogen (N), sulfur (S), and hydrogen (H) and having colorless crystals.

[0073] like Figure 2A As shown, thiourea (NH 2 CSNH 2 ) has a structure in which oxygen (O) in the urea molecular structure is replaced by sulfur (S), and has a molecular weight of 73.12 g / mol, a solubility of 142 g / L at 25°C, is easily soluble in water, and the thiourea aqueous solution is close to neutral. Thiourea itself can have antioxidant ability and can stabilize hydroxyl radicals.

[0074] For example, when the core 100 ( Figure 1 ) including cerium oxide (CeO 2 ) and thiourea (NH 2 CSNH 2 ) is used for the surface treatment of the core 100, as described in the following reaction formula 2, for example, thiourea (NH 2 CSNH 2 ) The surface of the core 100 is reduced to form an outer shell 200 ( Figure 1 middle).

[0075] [Reaction 2]

[0076] 2[NH 2 CSNH 2 ]+2CeO 2 +H 2 O

[0077] →[(NH 2 ) 2 CSSC(NH) 2 ](OH) 2 +Ce 2O 3

[0078] As described in the above reaction formula, on the surface of the core 100, thiourea (NH 2 CSNH 2 ) consists of a tetravalent cerium cation (Ce 4+ ) of cerium oxide (CeO 2 ) produces trivalent cerium cations (Ce 3+ ) of cerium oxide (Ce 2 O 3 ). Due to the presence of trivalent cerium cations (Ce on the surface of the core 100 (ie, the outer (shell) 200), 3+ ) ratio increases, so the above reaction formula 1 can be actively carried out, so that the antioxidant can have excellent hydroxyl radical stabilizing ability and excellent antioxidant ability.

[0079] like Figure 2B As shown, the thiourea-based compound according to an exemplary embodiment of the present invention may be pre-treated before the surface of the core 100 is subjected to the reduction treatment, and Figure 2B The thiourea dioxide (NH 2 C(=NH)SO 2 H) can be used as an example.

[0080] For example, cerium oxide (CeO 2 ) can be reduced by using thiourea (NH 2 CSNH 2 ) directly by surface treatment with an antioxidant, as described in reaction formula 2, or by using hydrogen peroxide (H 2 O 2 ) was pretreated to prepare thiourea dioxide (NH 2 C(=NH)SO 2 H), and then thiourea dioxide (NH 2 C(=NH)SO 2 H) Surface treatment with an antioxidant.

[0081] Preferably, the Figure 2A The thiourea (NH 2 CSNH 2 ) Add hydrogen peroxide (H 2 O 2 ) was pretreated to prepare thiourea dioxide (NH 2 C(=NH)SO 2 H), as described in the following reaction formula 3.

[0082] [Reaction 3]

[0083] NH 2 CSNH 2 +2H 2 O 2 →(NH 2 )C(=NH)SO 2 H+2H 2 O

[0084] Thiourea dioxide (NH 2 C(=NH)SO 2 H) has a molecular weight of 108.12 g / mol and a solubility of 30 g / L at 25 °C. 2 CSNH 2 ) compared to thiourea dioxide (NH 2 C(=NH)SO 2 H) has nearly white crystals, is easily soluble in water, and can therefore react with thiourea (NH 2 CSNH 2 ) in the same manner as in aqueous solution. Therefore, thiourea dioxide (NH 2 C(=NH)SO 2 H) can be easily applied to the surface treatment of granular antioxidants dispersed in deionized (DI) water. In addition, thiourea dioxide (NH 2 C(=NH)SO 2 H) may have hydrogen peroxide (H 2 O 2 ) and thiourea (NH 2 CSNH 2 ) and is used as a reducing agent or reducing agent. In addition, thiourea dioxide (NH 2 C(=NH)SO 2 H) is called formamidinesulfinic acid, and is known to be an organic sulfur compound used as an environmentally friendly material, which is widely used in textile manufacturing.

[0085] When the core 100 includes cerium oxide (CeO 2 ) and thiourea dioxide (NH 2 C(=NH)SO 2 H) For surface treatment of the core 100, the outer shell 200 may be treated by, for example, using thiourea dioxide (NH 2 C(=NH)SO 2 H) is formed by reducing the surface of the core 100, wherein the thiourea dioxide (NH 2 C(=NH)SO 2 H) by using hydrogen peroxide (H 2 O 2) is pretreated to obtain, as described in the following reaction formula 4-1.

[0086] [Reaction 4-1]

[0087] (NH 2 ) 2 CSO 2 H+2OH - →(NH 2 ) 2 CO+HSO 2 -

[0088] As described in the above reaction formula 4-1, thiourea dioxide (NH 2 C(=NH)SO 2 H) and hydroxyl ions (OH-) can react with each other in aqueous solution to produce urea ((NH 2 ) 2 CO) and sulfite ions (HSO 2 - ).

[0089] Thus, the outer shell 200 can be formed by using thiourea dioxide (NH 2 C(=NH)SO 2 H) includes cerium oxide (CeO 2 ) is formed by reducing the surface of the antioxidant, as described in the following reaction formula 4-2.

[0090] [Reaction 4-2]

[0091] 2HSO 2 - +2CeO 2 →2SO 2 +Ce 2 O 3 +H 2 O

[0092] When sulfite ions (HSO 2 - ) and tetravalent cerium cations (Ce 4+ ) of cerium oxide (CeO 2 ) react with each other, as described in reaction equation 4-2, sulfur dioxide (SO 2 ) and including trivalent cerium cations (Ce 3+ ) of cerium oxide (Ce 2 O 3 ).

[0093] In addition, thiourea (NH 2 CSNH 2 ) and thiourea dioxide (NH2 C(=NH)SO 2 H) has similar chemical properties to urea and can therefore be decomposed into ammonia (NH 3 ) and sulfur dioxide (SO 2 During fuel cell operation, ammonia (NH 3 ) and sulfur dioxide (SO 2 ) can be easily dissolved and discharged. Therefore, even a small amount of ammonia (NH 3 ) and sulfur dioxide (SO 2 ) remain on the surface of the antioxidant (ie, the exterior or shell 200), nor do they affect the performance of the fuel cell.

[0094] Figure 3 is a graph comparatively showing characteristics of antioxidants according to various exemplary embodiments of the present invention.

[0095] Figure 3 The figure shows the expected change in the properties of antioxidants by using thiourea dioxide (NH 2 C(=NH)SO 2 H) Cerium oxide (CeO) is formed on the surface of the antioxidant 2 ) is reduced to increase the antioxidant trivalent cerium cation (Ce 3 + ) content. If thiourea dioxide (NH 2 C(=NH)SO 2 H) increased from the antioxidant cerium oxide (CeO 2 ) converted into trivalent cerium cations (Ce 3+ ) content, the antioxidant ability of antioxidants to stabilize hydroxyl free radicals can be enhanced.

[0096] In addition, since the antioxidant capacity of the antioxidant is enhanced and the particle size of the antioxidant remains unchanged, the dissolution stability of the antioxidant can be maintained during the operation of the fuel cell. Therefore, a fuel cell can be manufactured by preparing an electrolyte membrane and an electrode including the above-mentioned antioxidant, and then providing the electrodes to both surfaces of the electrolyte membrane, and the prepared fuel cell (electrolyte membrane and electrode) can have increased chemical durability compared to a fuel cell using a conventional antioxidant. In particular, since the ionomer of the electrolyte membrane and the electrode of the membrane electrode assembly for the fuel cell can have a selective transport function of protons (hydrogen ions), as the trivalent cerium cation (Ce 3+ ) content increases, the antioxidant capacity of the antioxidant is enhanced, and thus, the fuel cell can have enhanced performance and chemical durability and extended service life.

[0097] Figure 4 is a flow chart showing an exemplary method for preparing an antioxidant for a fuel cell according to several embodiments of the present invention. Figures 1 to 3 A detailed description of some parts that are substantially the same as those in the examples above is not considered necessary.

[0098] In another aspect, a method for preparing an antioxidant for a fuel cell is provided. The method may include preparing a first admixture comprising a metal component and preparing a second admixture comprising a reducing agent. The metal component may be present in the form of particles having a predetermined size, for example, about 5 nm to 100 nm, as measured by X-ray diffraction (XRD) or Brunauer-Emmett-Teller (BET) method.

[0099] The dispersion may include a metal component as an antioxidant precursor, wherein the metal component is a metal oxide (M x O k ) and composite metal oxides (M x N y O j , N and M are different metals), the antioxidant precursor is further subjected to surface treatment. The second admixture may include a reducing agent, deionized water and a pH adjuster, the reducing agent including a thiourea-based compound.

[0100] For example, Figure 4 As shown, the preparation method may include: preparing a dispersed solution containing a metal component (S11 and S13); preparing a reducing agent for surface treatment (S17); and preparing an antioxidant with a surface subjected to reduction treatment by mixing the solution for surface treatment with an antioxidant dispersion (S21 and S23).

[0101] The preparation method according to various exemplary embodiments of the present invention may include: preparing a first admixture (S11) including a metal component (e.g., a metal oxide and a composite metal oxide) that may constitute the core of an antioxidant and deionized water, for example, by mixing the metal component and the deionized water to prepare the first admixture; preparing a dispersion liquid including an antioxidant by dispersing a first mixed liquid (S13); preparing a second admixture including a dispersion liquid and a reducing agent, for example, by mixing the dispersion liquid and the reducing agent to reduce the surface of the antioxidant to prepare the second admixture (S21); and preparing an antioxidant whose surface is subjected to reduction treatment by drying the second mixed liquid (S23). Preferably, the reducing agent may appropriately include a thiourea-based compound.

[0102] The outer shell 200 may be formed on the surface of the antioxidant that has completed the reduction treatment, and the outer shell 200 includes a metal cation (M (x-n)+, n is a natural number of 1 or greater), the metal cation has an oxidation number smaller than the metal oxide (M x O k ) or composite metal oxide (M x N y O j ) includes the valence of the metal M.

[0103] Preparing a dispersion liquid including a metal component (S13) may include placing the prepared first mixed solution in an ionomer dispersion liquid having a pH of about 2.5 or greater. For example, a particulate antioxidant including cerium oxide or composite cerium oxide may be dispersed in an aqueous solution, and then the prepared mixed solution may be placed in an ionomer dispersion liquid having a pH of about 2.5 or greater (e.g., an ionomer dispersion liquid included in an electrolyte membrane or an electrode). Since the dissolution stability of the antioxidant may be reduced when the mixed solution is placed in an ionomer dispersion liquid having a pH of less than about 2.5, the mixed solution may be appropriately placed in an ionomer dispersion liquid having a pH of about 2.5 or greater.

[0104] In addition, during the preparation of the dispersion liquid (S13) including the antioxidant, a nanodispersor can be used to disperse the antioxidant. For example, a nanodispersor can be used to disperse the antioxidant by 6-cycle dispersion under the condition of D50, so that the particle size of the antioxidant is reduced from about 3 μm to about 0.2 μm.

[0105] In addition, during the preparation of the second mixed solution (S21), an appropriate amount of the antioxidant dispersion and the solution for surface treatment may be mixed and stirred for an appropriate time (e.g., 4 hours), and then centrifuged to produce a solid. In addition, after the preparation of the second mixed solution (S21), washing and drying may be performed, thereby finally preparing a solid having an increased content of trivalent cerium cations (Ce 3+ ) of a metal oxide (e.g., cerium oxide) or a composite metal oxide antioxidant.

[0106] In particular, the preparation of the second mixed solution (S21) according to various exemplary embodiments of the present invention, i.e., the surface treatment of the antioxidant, can be carried out in the range of about 5 to 11 at pH. When the surface treatment of the antioxidant is carried out in the range of about 3 or less at pH or in the range of about 11 or more at pH, it may be difficult to handle the material during the preparation of the antioxidant. Therefore, the surface treatment of the antioxidant can be carried out in the range of about 5 to 11 at pH, or in particular, in the range of about 6 to 8 at pH. When the surface treatment of the antioxidant is carried out in the range of about 6 to 8 at pH, a small amount of antioxidant may show a significant effect under conditions close to neutrality. Alternatively, the surface treatment of the antioxidant can be carried out in the range of about 8 to 9 at pH, i.e., under weakly alkaline conditions.

[0107] In addition, the preparation of the second admixture (S21) can be carried out at a temperature in the range of about 10°C to 80°C. Since the liquid can evaporate under the condition of a temperature of about 80°C or higher, the preparation of the second admixture (S21) can be carried out at a temperature of less than about 80°C. In addition, the surface treatment of the antioxidant can be fully carried out in a room temperature atmosphere. In addition, at a temperature below room temperature, the surface treatment effect may be reduced and a cooling treatment may be required. In addition, within the above temperature range, as the temperature increases, the antioxidant capacity of the antioxidant can be enhanced. Therefore, the surface treatment and reaction associated with it (S21) can be carried out within a temperature range of room temperature to about 80°C, or in particular, within a temperature range of room temperature to 60°C.

[0108] For example, when the antioxidant includes cerium oxide (CeO 2 ), the reaction described in the above reaction formula 2 can be carried out in the preparation of the second admixture (S21).

[0109] After the reaction, on the surface of the antioxidant, tetravalent cerium cations (Ce 4+ ) of cerium oxide (CeO 2 ) through thiourea (NH 2 CSNH 2 ) will produce trivalent cerium cations (Ce 3+ ) of cerium oxide (Ce 2 O 3 ). Therefore, the trivalent cerium cation (Ce 3+ ) content, thereby improving the antioxidant capacity of antioxidants.

[0110] In addition, if Figure 4 As shown, the preparation method according to various exemplary embodiments of the present invention may further include: before preparing the second admixture (S21), preparing a solution for surface treatment including a reducing agent (e.g., a thiourea-based compound) by mixing the reducing agent with deionized (DI) water and a pH adjuster (S17).

[0111] For example, thiourea dioxide (NH 2 C(=NH)SO 2 H) as a thiourea-based compound to prepare a solution for surface treatment (S17). During the preparation of the solution for surface treatment (S17), a certain amount of solid thiourea dioxide (NH4H4) within the solubility range can be added. 2 C(=NH)SO 2H) is placed in deionized water to prepare a solution for surface treatment, and then a pH regulator can be additionally added to the solution for surface treatment, and then the solution for surface treatment can be stirred, so that the pH of the solution for surface treatment can be adjusted. As the pH regulator, various substances with different contents, such as sulfuric acid and sodium hydroxide, can be used.

[0112] In addition, preparing the solution for surface treatment (S17) may include: using hydrogen peroxide (H 2 O 2 ) is used to pre-treat the solution for surface treatment. That is, before preparing the second admixture (S21), a solution using hydrogen peroxide (H 2 O 2 ) a pretreated solution for surface treatment (S17).

[0113] For example, by pre-treatment, hydrogen peroxide (H 2 O 2 ) thiourea (NH 2 CSNH 2 ) is pretreated to produce thiourea dioxide (NH 2 C(=NH)SO 2 H), as described in the above reaction formula 4-1. Thus, during the preparation of the second admixture (S21), a surface having an increased content of trivalent cerium cations (Ce 3+ ) as described in reaction formula 4-2.

[0114] Example

[0115] Hereinafter, the present invention will be described in more detail by the following examples and comparative examples. The following examples are only used to exemplarily describe the present invention and are not intended to limit the scope of the present invention.

[0116] Manufacturing Example: Antioxidant Comprising Metal Oxides Surface Treated with Thiourea-Based Compounds Preparation of

[0117] 1-1) Thiourea-based compounds

[0118] In the manufacturing example, thiourea dioxide (CAS No.: 1758-73-2) manufactured by Sigma Aldrich was dissolved in an aqueous solution and then used for the surface treatment of the antioxidant.

[0119] 1-2) Antioxidants

[0120] In the manufacturing example, among the metal oxides, cerium oxide (CAS No.: 1306-38-3) having a crystal size of 25 nm as measured by X-ray diffraction (XRD) was used as an antioxidant.

[0121] 1-3) Manufacturing process

[0122] First, during the preparation of the antioxidant dispersion, a nanodispersor is used to disperse a particulate antioxidant. In this case, the antioxidant is dispersed by 6 cycles of dispersion under the condition of D50 using the nanodispersor, so that the particle size of the antioxidant is reduced from about 3 μm to about 0.2 μm.

[0123] In addition, in the step of preparing the solution for surface treatment, a certain amount of solid thiourea dioxide (NH 2 C(=NH)SO 2 H) was put into deionized (DI) water to prepare a thiourea dioxide solution, and then different contents of 0.1 M sulfuric acid and 0.1 M sodium hydroxide were additionally added to the thiourea dioxide solution as pH adjusters, and then the thiourea dioxide solution was stirred, so that the pH of the thiourea dioxide solution could be adjusted to a set value.

[0124] Thereafter, during the period of mixing the antioxidant dispersion and the solution for surface treatment and performing surface treatment, samples of the antioxidant dispersion and the thiourea dioxide solution used as the solution for surface treatment were prepared according to the respective blends, and then mixed and stirred for 4 hours, and then centrifuged to produce a solid. Thereafter, a washing treatment using deionized water and a drying treatment were performed to obtain a solid having trivalent cerium cations (CeO2) ionized by thiourea dioxide. 3+ ) with an increased content of cerium oxide.

[0125] 1-3) Manufacturing Examples and Comparative Examples

[0126] The antioxidant of Comparative Example 1 was prepared by dispersing cerium oxide in an aqueous solution using deionized water without surface treatment using thiourea dioxide, performing centrifugation to produce a solid, and drying the solid particles.

[0127] In the antioxidants of Examples 1 to 5 prepared by the above-mentioned preparation method, 10 g of 1% antioxidant dispersion was used. In addition, in order to increase the trivalent cerium cation (Ce 3+ ) content, a 2% thiourea dioxide solution was prepared, and 0.25 g, 0.50 g, 1.00 g, 2.00 g and 5.00 g of the thiourea dioxide solution were mixed with the antioxidant dispersion to prepare the cerium oxide-thiourea dioxide blends in Examples 1, 2, 3, 4 and 5. The surface-treated cerium oxide was prepared by stirring the prepared blend at room temperature for 4 hours, then centrifuging, washing with deionized water and drying at 80°C.

[0128] Evaluation Example 1: Results of cerium oxide surface treatment depending on the content of thiourea dioxide

[0129] Figure 5 is an image showing cerium oxide surface treated with thiourea dioxide according to the above-mentioned manufacturing example. Figure 5 Starting from the left side of , the sample of the comparative example and the samples of Examples 1 to 5 prepared according to the manufacturing examples are shown in order.

[0130] like Figure 5 As shown exemplarily, it can be confirmed that as the content of thiourea dioxide increases during the surface treatment, the color of the cerium oxide surface darkens from light yellow to dark yellow and then to light brown.

[0131] Evaluation Example 2: Evaluation of Antioxidant Capacity of Cerium Oxide Depending on Thiourea Dioxide Content

[0132] 2-1) Test conditions

[0133] In order to quantify the antioxidant properties of antioxidants, various methods can be applied. In this evaluation example, methyl violet (MV) manufactured by Sigma Aldrich (CAS No.: 8004-87-3), iron (II) sulfate heptahydrate manufactured by Sigma Aldrich (FeSO 4 7H 2 O) (CAS No. 7782-63-0), and hydrogen peroxide (H 2 O 2 ) (CAS No. 7722-84-1) to compare the antioxidant properties of antioxidants. To prepare the reagent, 0.5 g of 9.0 × 10 -3 M iron (II) sulfate heptahydrate and 0.5 g of 9.0 × 10 -3 M hydrogen peroxide to generate hydroxyl radicals, 3 mg of the previously prepared cerium oxide was placed in a corresponding container, and then 9 g of 2×10 -5 M methyl violet was placed in a corresponding container, thereby producing 10 g of an antioxidant sample to verify the antioxidant properties. The color change of the sample was confirmed after 24 hours, and after removing the cerium oxide deposit, the properties of the sample were quantified using a UV-visible spectrophotometer (Hitachi U-2900).

[0134] 2-2) Evaluation results

[0135] like Figure 6As shown, it is possible to determine whether the hydroxyl radical is stabilized by an antioxidant and the stability of the hydroxyl radical by using the evaluation result obtained by using methyl violet. Methyl violet was originally purple, but when reacted by hydroxyl radicals, methyl violet loses its original color and becomes colorless, while stabilizing the hydroxyl radicals. Therefore, if the hydroxyl radicals are stabilized in advance by an antioxidant, methyl violet shows its original color, i.e. purple, and the free radical stabilizing ability (i.e. antioxidant ability) of the antioxidant can be determined according to the intensity of the color presented by methyl violet. For reference, this evaluation method is similar to the Fenton test method, one of the chemical durability tests of fuel cell electrolyte membranes.

[0136] like Figure 6 As shown exemplarily, depending on whether thiourea dioxide is used for surface treatment, the degree of antioxidant capacity of cerium oxide can be evaluated according to the color of methyl violet used as a reagent. The color of the reagent in the cerium oxide of each embodiment is a deeper purple than the color of the reagent in the cerium oxide of the comparative embodiment without surface treatment, and in particular, the cerium oxide of Examples 3, 4 and 5 exhibits high antioxidant properties. It can be understood that as the content of thiourea dioxide introduced for surface treatment of cerium oxide increases, the reaction is effectively carried out, and the trivalent cerium cation (Ce) on the surface of cerium oxide is increased. 3+ ) content increases, thereby enhancing the antioxidant capacity of the antioxidant.

[0137] In addition, the cerium oxide of Example 5 (using 5.00g of thiourea dioxide) shows a slight decrease in antioxidant capacity. It is speculated that the reason is that the surface of the cerium oxide is covered with an excess of thiourea dioxide, so the thickness of the covering layer reduces the free radical stabilization reaction of the cerium oxide. Otherwise, it is judged that when the weight of the cerium oxide is measured, the weight of the cerium oxide includes a portion of the weight of thiourea dioxide, so the absolute amount of the cerium oxide is reduced. Therefore, it can be understood that the ratio of the content of thiourea dioxide to the weight of the cerium oxide can be 5 to 100%, in particular, 20 to 100%, thereby showing high antioxidant capacity.

[0138] Evaluation Example 3: Quantitative Evaluation of Antioxidant Capacity of Cerium Oxide Depending on Thiourea Dioxide Content

[0139] like Figure 7 As shown, in order to quantitatively compare the antioxidant capacity of the cerium oxide of the example and the example, the purple intensity of the reagent in the evaluation example 2 was quantitatively measured using a UV-visible spectrophotometer. In this evaluation example, the antioxidant capacity of the cerium oxide was compared using a UV-visible spectrophotometer. The following Table 1 shows the values ​​at the maximum absorbance.

[0140] Table 1

[0141]

[0142]

[0143] As shown in Table 1 above, it can be understood that, relative to the cerium oxide of the comparative example, the cerium oxides of Examples 3 and 5 have an antioxidant capacity enhanced by about 100%, and the cerium oxide of Example 4 has an antioxidant capacity enhanced by about 120%.

[0144] Evaluation Example 4: Evaluation of Antioxidant Ability of Cerium Oxide Depending on Surface Treatment Conditions

[0145] In order to verify the properties of cerium oxide depending on pH and temperature conditions, the ratio of thiourea dioxide to cerium oxide was usually fixed at 40% (0.04 g of thiourea dioxide / 0.1 g of cerium oxide).

[0146] In the case of pH conditions, the temperature was fixed at 25° C., and when preparing the thiourea dioxide aqueous solution, a 0.1 M sulfuric acid aqueous solution and a 0.1 M sodium hydroxide aqueous solution were added to adjust the pH conditions.

[0147] Under temperature conditions, the pH was fixed at 7.

[0148] 4-1) Evaluation results depending on pH conditions

[0149] The antioxidative properties of the cerium oxide depending on the surface treatment conditions of the cerium oxide using thiourea dioxide were verified by changing the pH conditions, and the verification results are shown in Table 2 below.

[0150] Table 2

[0151]

[0152]

[0153] As shown in Table 2 above, it can be understood that as the pH increases, the trivalent cerium cations (Ce 3+ ) is greater than the tetravalent cerium cation (Ce 4+ ) content, so the antioxidant capacity of cerium oxide is enhanced, thereby hydroxyl ions (OH - ) plays an important role in surface reactions.

[0154] On the other hand, compared with the comparative example, cerium oxide exhibits excellent performance under an acidic atmosphere (Table 1). Therefore, since it may be difficult to process the material for preparing the antioxidant at a low pH of 3 or less or at a high pH of 11 or more, it can be determined that a pH condition of 6 to 8 (close to a neutral condition, in which case a small amount of antioxidant may exhibit a significant effect) or a weakly alkaline condition of pH 8 to 9 is suitable.

[0155] 4-2) Evaluation results depending on temperature conditions

[0156] The antioxidative properties of the cerium oxide depending on the surface treatment conditions of the cerium oxide using thiourea dioxide were verified by changing the temperature conditions, and the verification results are shown in Table 3 below.

[0157] Table 3

[0158]

[0159] As shown in Table 3 above, it can be understood that the antioxidant capacity of cerium oxide increases with increasing temperature. It can be confirmed that cerium oxide exhibits sufficiently excellent properties even at room temperature compared to the comparative example (Table 1). Since the solution may evaporate at a temperature of 80°C or higher, a temperature condition below 80°C is suitable, and thus the surface treatment effect is reduced, and since a cooling process is required under a temperature condition below room temperature, a temperature condition below room temperature is not suitable. Therefore, a temperature condition of room temperature to 80°C, or in particular, a temperature condition of room temperature to 60°C can be appropriately used during the preparation process to exhibit antioxidant capacity.

[0160] According to various exemplary embodiments of the present invention, a surface-treated antioxidant and a preparation method thereof are provided to enhance antioxidant capacity while having a particle size that ensures dissolution stability. Therefore, when the antioxidant is used in an ionomer of an electrolyte membrane or an electrode, the performance and chemical durability of a membrane electrode assembly can be enhanced, thereby enhancing the performance and durability of a fuel cell including a membrane electrode assembly, and the service life of the fuel cell can be extended.

[0161] In addition, the antioxidant for a fuel cell according to various exemplary embodiments of the present invention may be surface-treated using a thiourea-based compound to form an outer portion (eg, a shell) including a larger content of reduced metal oxide than a core, thereby enhancing antioxidant capability.

[0162] Furthermore, the surface-treated antioxidant may have a particle size that ensures dissolution stability while providing high antioxidant capacity.

[0163] Furthermore, when the surface-treated antioxidant includes a metal oxide having the same crystal size, the antioxidant may provide excellent antioxidant capacity compared to other antioxidants.

[0164] Furthermore, when an antioxidant is used in an ionomer of an electrolyte membrane or an electrode, the performance and chemical durability of a membrane electrode assembly can be enhanced, and thereby the performance and durability of a fuel cell including the membrane electrode assembly can be enhanced and the service life of the fuel cell can be extended.

[0165] The present invention has been described in detail with reference to various exemplary embodiments of the present invention. However, it should be appreciated that changes may be made to these embodiments by those skilled in the art without departing from the principles and spirit of the present invention, the scope of the present invention being limited in the appended claims and their equivalents.

Claims

1. An antioxidant for a fuel cell, comprising: The core comprises one selected from metal oxides, composite metal oxides and combinations thereof, wherein the metal oxide is M x O k , the composite metal oxide is M x N y O j , wherein N and M are different metals; and The outer portion is located on or above the surface of the core and includes an outer portion formed by M (x-n)+ A metal cation represented by wherein n is a natural number of 1 or greater, and the metal cation has an oxidation number less than the valence of the core metal M; wherein the outer portion is formed by performing a reduction treatment on the surface of the core portion using a reducing agent, Wherein, the reducing agent comprises a thiourea-based compound, wherein the thiourea-based compound comprises i) carbon, ii) an amine group and iii) sulfur.

2. The antioxidant for a fuel cell according to claim 1, wherein The metal M includes cerium; and the core includes Ce 4+ The compound, the outer portion includes Ce 3+ of compounds.

3. The antioxidant for a fuel cell according to claim 1, wherein The composite metal oxide includes one or more selected from the group consisting of cerium zirconium oxide, gadolinium-doped cerium oxide, samarium-doped cerium oxide, titanium dioxide-supported cerium oxide, and silicon dioxide-supported cerium oxide.

4. The antioxidant for a fuel cell according to claim 1, wherein The crystal size of each of the metal oxide and the composite metal oxide measured by an X-ray diffraction method or a BET method is 5 nm to 100 nm.

5. The antioxidant for a fuel cell according to claim 1, wherein The antioxidant is formed as agglomerated particles having a size of 10 nm to 500 nm.

6. The antioxidant for a fuel cell according to claim 1, wherein The core includes Ce 4+ CeO2; the outer portion includes Ce 3+ of Ce2O3.

7. A membrane electrode assembly comprising: an electrolyte membrane and electrodes, the electrodes being formed on both surfaces of the electrolyte membrane, At least one of the electrolyte membrane or the electrode comprises the antioxidant according to claim 1.

8. A method for preparing an antioxidant for a fuel cell, the method comprising: A first admixture is prepared, wherein the first admixture includes i) a metal component, wherein the metal component includes one selected from metal oxides, composite metal oxides, and combinations thereof, wherein the metal oxide is M x O k , the composite metal oxide is M x N y O j , wherein N and M are different metals; and ii) deionized water; preparing a dispersion by dispersing the first blend; preparing a second admixture comprising the dispersion and a reducing agent; Performing reduction treatment on the surface of the metal component; as well as drying the second blend to obtain an antioxidant; Wherein, the reducing agent comprises a thiourea-based compound, wherein the thiourea-based compound comprises i) carbon, ii) an amine group and iii) sulfur.

9. The method according to claim 8, wherein: The antioxidant has a core and an outer portion, wherein the core includes a metal component and the outer portion includes a metal component. (x-n)+ A metal cation represented by wherein n is a natural number of 1 or greater, the metal cation having an oxidation number less than the valence of the metal M of each of the metal oxide and the composite metal oxide in the core, wherein the metal oxide is M x O k , the composite metal oxide is M x N y O j .

10. The method according to claim 8, wherein: The thiourea-based compound includes one or more selected from thiourea, thiourea dioxide, 1,3-diisopropyl-2-thiourea, 1-(2-methoxyphenyl)-2-thiourea, propylenethiourea, and 1-(2-furfuryl)-2-thiourea.

11. The method according to claim 8, wherein: Preparing the dispersion includes combining the first admixture and an ionomer dispersion having a pH above 2.

5.

12. The method according to claim 8, wherein: Preparation of the dispersion involves the use of a nanodisperser.

13. The method according to claim 8, wherein: The preparation of the second blend is carried out in the pH range of 5 to 11.

14. The method according to claim 8, wherein: The preparation of the second blend is carried out at a temperature ranging from 10°C to 80°C.

15. The method according to claim 8, wherein: The metal component includes CeO2; and During the reduction treatment, the reaction shown in the following reaction formula 2 occurs: [Reaction 2] 2[NH2CSNH2]+2CeO2+H2O→[(NH2)2CSSC(NH)2](OH)2+Ce2O3.

16. The method according to claim 15, further comprising: Prior to preparing the second admixture, a reducing agent is prepared by mixing a thiourea-based compound, deionized water, and a pH adjuster.

17. The method according to claim 16, wherein: Prior to the reduction treatment, the reducing agent is pretreated with hydrogen peroxide.

18. The method according to claim 17, wherein: The reducing agent is pretreated by the reaction shown in Formula 4-1: [Reaction formula 4-1] NH2C(=NH)SO2H+2OH - →(NH2)2CO+HSO2 - 。 19. The method according to claim 18, wherein: The reduction treatment is performed by using the reaction product of Formula 4-1 as a reactant in the reaction shown in Formula 4-2, [Reaction Formula 4-2] <h2 style=";text-align:left;direction:ltr">2HSO2<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> +2CeO2→2SO2+Ce2O3+H2O.

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