Membrane-Electrode Assembly for Fuel Cell and Method of Manufacturing the Same

Abstract

The present disclosure relates to a membrane-electrode assembly for a fuel cell and a method of manufacturing the same, and more particularly, to a membrane-electrode assembly that applies an electrolyte membrane including cerium oxide and phosphoric acid-functionalized graphene oxide, thereby improving the chemical durability and proton conductivity of the membrane-electrode assembly.

Description

Technical Field

[0001] The present disclosure relates to a membrane - electrode assembly for a fuel cell and a method of manufacturing the same, and more particularly, to a membrane - electrode assembly that applies an electrolyte membrane including cerium oxide and phosphoric acid functionalized graphene oxide, thereby improving the chemical durability and proton conductivity of the membrane - electrode assembly. Background Art

[0002] A polymer electrolyte membrane fuel cell for a vehicle is a power generation device that generates electricity through an electrochemical reaction between hydrogen and oxygen in the air. It is well known that a polymer electrolyte membrane fuel cell for a vehicle is an environmentally friendly next - generation energy source that exhibits high power generation efficiency and has no exhaust gas substances other than water. In addition, a polymer electrolyte membrane fuel cell generally operates at a temperature below 95 °C and can have a high output density. The reaction that generates electricity in a fuel cell occurs on a membrane - electrode assembly (MEA) that includes a perfluorosulfonic acid (PFSA) ionomer - based electrolyte membrane and an anode / cathode. Hydrogen supplied to the anode of the fuel cell as an oxidation electrode is divided into protons and electrons. Protons move through the membrane to the cathode as a reduction electrode, and electrons move through an external circuit to the cathode. At the cathode, oxygen molecules, protons, and electrons react with each other to generate electricity and heat, and water (H2O) is generated as a reaction by - product.

[0003] Generally, hydrogen and oxygen in the air as reaction gases of a fuel cell can pass through the electrolyte membrane and undergo crossover, thereby accelerating the generation of hydrogen peroxide (HOOH). Hydrogen peroxide (HOOH) generates oxygen - containing free radicals such as hydroxyl radicals (·OH) and hydroperoxyl radicals (·OOH). The free radicals attack the perfluorosulfonic acid electrolyte membrane, thereby causing chemical degradation of the electrolyte membrane and ultimately reducing the durability of the fuel cell (DE Curtin et al., J. Power Sources, 131, 41 - 48 (2004); A.P. Young et al., J. Electrochem. Soc., 157, B425 - B436 (2010); P. Trogadas et al., Electrochem. Solid - State Lett., 11, B113 - B116 (2008); R. Uegaki et al., J. Power Sources, 196, 9856 - 9861 (2011); D. Zhao et al., J. Power Sources, 190, 301 - 306 (2009)).

[0004] Conventionally, a method of adding various antioxidants to an electrolyte membrane has been used as a technique for mitigating chemical degradation of the electrolyte membrane and the membrane-electrode assembly.

[0005] The antioxidants include a first antioxidant having a free radical scavenger function and a second antioxidant having a hydrogen peroxide decomposer function.

[0006] The first antioxidant includes cerium-based antioxidants such as cerium oxide hexahydrate or cerium(III) nitrate, and terephthalic acid-based antioxidants. The second antioxidant includes manganese-based antioxidants such as manganese oxide.

[0007] However, in the case of adding the above-mentioned antioxidants to mitigate chemical degradation of the electrolyte membrane and the membrane-electrode assembly, the proton conductivity of the electrolyte membrane decreases.

[0008] The above information disclosed in this background art section is provided only to enhance understanding of the background of the present disclosure, and thus may include information that does not constitute the prior art known to those skilled in the art. SUMMARY OF THE INVENTION

[0009] The present disclosure is made to solve the above problems related to the prior art.

[0010] An object of the present disclosure is to provide an electrolyte membrane that exhibits higher chemical durability and proton conductivity than conventional perfluorosulfonic acid ionomer-based electrolyte membranes such as Nafion, and a membrane-electrode assembly including the electrolyte membrane.

[0011] The object of the present disclosure is not limited to the above object. The object of the present disclosure will be clearly understood from the following description, and the object of the present disclosure can be achieved by the means defined in the claims and their combinations.

[0012] In one aspect, the present disclosure provides a membrane-electrode assembly for a fuel cell, the membrane-electrode assembly including: an electrolyte membrane; and a pair of electrodes disposed on opposite surfaces of the electrolyte membrane, wherein the electrolyte membrane includes cerium oxide and phosphoric acid-functionalized graphene oxide.

[0013] The electrolyte membrane may include a perfluorosulfonic acid (PFSA) ionomer.

[0014] The cerium oxide and the phosphoric acid-functionalized graphene oxide may have a structure in which the cerium oxide is distributed on the surface of the graphene oxide and the phosphoric acid is bonded to the oxygen element included in the functional groups of the graphene oxide.

[0015] The electrolyte membrane may include 0.01 wt% to 20.0 wt% of the functionalized graphene oxide.

[0016] The electrolyte membrane may include: a porous reinforcing layer impregnated with an ion transfer material and functionalized graphene oxide; and an ion transfer layer disposed on at least one surface of the reinforcing layer, the ion transfer layer including an ion transfer material and functionalized graphene oxide.

[0017] The reinforcing layer may include any one selected from the group consisting of polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (e-PTFE), polyethylene (PE), polypropylene (PP), polyphenylene oxide (PPO), polybenzimidazole (PBI), polyimide (PI), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and combinations thereof.

[0018] In another aspect, the present disclosure provides a method for manufacturing a membrane-electrode assembly for a fuel cell, the method including: preparing cerium oxide and phosphoric acid-functionalized graphene oxide; mixing the functionalized graphene oxide with an ion transfer material; manufacturing an electrolyte membrane using the mixture; and forming electrodes on opposite surfaces of the electrolyte membrane.

[0019] Preparing cerium oxide and phosphoric acid-functionalized graphene oxide may include: (a) functionalizing graphene oxide with phosphoric acid; and (b) functionalizing graphene oxide with cerium oxide.

[0020] Functionalizing graphene oxide with phosphoric acid may include: mixing a phosphoric acid precursor material and graphene oxide to prepare a first mixture; introducing an active additive into the first mixture to prepare a second mixture; separating the second mixture into a liquid material and a solid material; drying the separated solid material to prepare a solid powder; and washing the solid powder to obtain phosphoric acid-functionalized graphene oxide (PGO).

[0021] Functionalizing graphene oxide with cerium oxide may include: mixing a cerium precursor material and graphene oxide to prepare a third mixture; and reacting the third mixture to obtain cerium oxide-functionalized graphene oxide.

[0022] The phosphoric acid precursor material may include triethylphosphite (P(OEt)3).

[0023] The first mixture can be prepared by mixing 100 parts by weight of the phosphoric acid precursor material with 0.1 to 2.0 parts by weight of graphene oxide with each other.

[0024] The active additive can include lithium bromide (LiBr).

[0025] Based on 100 parts by weight of the phosphoric acid precursor material, 0.1 to 5.0 parts by weight of the active additive can be added.

[0026] The cerium precursor material can include cerium nitrate hexahydrate (Ce(NO3)3·6H2O).

[0027] The third mixture can be prepared by mixing 100 parts by weight of graphene oxide with 1.0 to 20.0 parts by weight of the cerium precursor material with each other.

[0028] Manufacturing the electrolyte membrane can include: coating the mixture on a substrate.

[0029] Manufacturing the electrolyte membrane can include: impregnating the mixture into a porous reinforcing layer; and coating the mixture on at least one surface of the reinforcing layer. Description of the Drawings

[0030] The above and other features of the present disclosure will now be described in detail with reference to some exemplary embodiments of the present disclosure shown in the drawings, which are given by way of illustration only and thus do not limit the present disclosure, and in which:

[0031] Figure 1 is a schematic cross-sectional view of a membrane-electrode assembly according to the present disclosure;

[0032] Figure 2 is a cross-sectional view of an electrolyte membrane according to an embodiment of the present disclosure;

[0033] Figure 3 is a view schematically showing phosphoric acid-functionalized graphene oxide;

[0034] Figure 4 is a cross-sectional view of an electrolyte membrane according to another embodiment of the present disclosure;

[0035] Figure 5 is a flowchart schematically showing a method for manufacturing a membrane-electrode assembly for a fuel cell according to the present disclosure;

[0036] Figure 6A , Figure 6B , Figure 6C and Figure 6D are photos showing electrolyte membranes manufactured according to Example 1-1, Example 1-2, Example 1-3, and Example 1-4, respectively;

[0037] Figure 7 is a view showing measurement results of temperature-based hydrogen ion conductivity of electrolyte membranes manufactured according to Examples 1-1 to 1-4 and Comparative Examples; and

[0038] Figure 8 is a view showing measurement results of time-based fluoride emission rates of electrolyte membranes manufactured according to Example 1-4, Example 2, and Comparative Examples.

[0039] It should be understood that the drawings are not necessarily drawn to scale and show a somewhat simplified representation of various preferred features illustrating the basic principles of the present disclosure. Specific design features of the present disclosure disclosed herein, including, for example, specific dimensions, orientations, positions, and shapes, will be determined in part by the particular intended application and use environment.

[0040] In the drawings, throughout several views of the drawings, reference numerals refer to the same or equivalent parts of the present disclosure. Detailed Description

[0041] From the following preferred embodiments with reference to the drawings, the above objects and other objects, features, and advantages will be clearly understood. However, the present disclosure is not limited to these embodiments and will be implemented in different forms. These embodiments are presented only to provide a thorough and complete understanding of the disclosed content and to sufficiently inform those skilled in the art of the technical concept of the present disclosure.

[0042] Throughout the description of the drawings, the same reference numerals refer to the same elements. In the drawings, the dimensions of the structures are exaggerated for clarity. It will be understood that although the terms "first", "second", etc. may be used herein to describe various elements, the corresponding elements should not be understood to be limited by these terms, which are only used to distinguish one element from another. For example, within the scope defined by the present disclosure, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element. Unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms.

[0043] It will be further understood that when the terms "comprising", "having", etc. are used in this specification, they specify the presence of the stated features, quantities, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, operations, elements, components, or combinations thereof. Additionally, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element may be directly on the other element or there may also be intervening elements. It will also be understood that when an element such as a layer, film, region, or substrate is referred to as being "under" another element, the element may be directly under the other element or there may also be intervening elements.

[0044] Unless otherwise clearly indicated by the context, all quantities, numbers, and / or expressions representing components, reaction conditions, polymer compositions, and amounts of mixtures used in this specification are approximate values, and the approximate values reflect the various measurement uncertainties inherently occurring when obtaining these numbers. Therefore, it should be understood that in all cases, the term "about" should modify all quantities, numbers, and / or expressions. Additionally, when a numerical range is disclosed in the specification, unless otherwise defined, these ranges are continuous and include all numbers from the minimum value to the maximum value, including the maximum value within the range. Furthermore, when the range refers to integers, unless otherwise defined, the range includes all integers from the minimum value to the maximum value, including the maximum value within the range.

[0045] Figure 1 is a cross-sectional view schematically showing a membrane-electrode assembly according to the present disclosure. Referring to this figure, the membrane-electrode assembly includes an electrolyte membrane 1 and a pair of electrodes 2 disposed on opposite surfaces of the electrolyte membrane 1. Here, the "pair of electrodes" refers to an anode and a cathode disposed opposite to each other based on the electrolyte membrane.

[0046] Figure 2 is a cross-sectional view showing the electrolyte membrane 1 according to an embodiment of the present disclosure. Referring to this figure, the electrolyte membrane 1 includes an ion transfer material 10 and cerium oxide and phosphoric acid-functionalized graphene oxide (hereinafter referred to as "functionalized graphene oxide") 20.

[0047] The ion transfer material 10 may include any material capable of transferring hydrogen ions. For example, the ion transfer material 10 may include a perfluorosulfonic acid (PFSA) ionomer.

[0048] The functionalized graphene oxide 20 is dispersed in the ion transfer material 10. Therefore, the water absorption rate of the electrolyte membrane 1 increases, and the hydrogen ion conductivity and chemical durability of the electrolyte membrane 1 are improved.

[0049] Generally, graphene, as a material in which carbon is bonded in a two-dimensional honeycomb structure, has the basic form of a carbon-carbon bonded material, while graphene oxide has a form in which functional groups such as carboxyl, hydroxyl, or epoxy groups are bonded to graphene.

[0050] In this specification, "functionalized" means that cerium oxide and / or phosphoric acid is associated with graphene oxide, and its meaning will be more clearly understood from the following description.

[0051] Cerium oxide-functionalized graphene oxide may be graphene oxide on the surface of which cerium oxide is distributed. Specifically, it may be that after a precursor of cerium oxide approaches the surface of graphene oxide, it grows into cerium oxide. Cerium oxide may adhere to the surface of graphene oxide, may be bonded to the carbon element of graphene oxide, or may be bonded to the functional group of graphene oxide.

[0052] Cerium oxide has the function of a radical scavenger. When functionalized graphene oxide with cerium oxide is applied to the electrolyte membrane 1, the chemical durability of the electrolyte membrane 1 can be significantly improved.

[0053] Phosphoric acid-functionalized graphene oxide may have a structure in which phosphoric acid is bonded to the oxygen element included in the functional groups of graphene oxide. Figure 3 is a view schematically showing phosphoric acid-functionalized graphene oxide. Here, a carboxyl group is represented as a functional group. However, the present disclosure is not limited thereto.

[0054] Referring to this figure, graphene oxide includes oxygen-containing functional groups selected from the group consisting of carboxyl groups, hydroxyl groups, epoxy groups, and combinations thereof. Phosphoric acid-functionalized graphene oxide is formed by covalent bonding between phosphoric acid and the oxygen of the oxygen-containing functional group.

[0055] Since phosphoric acid is directly covalently bonded to the oxygen-containing functional group of graphene oxide, the number of phosphate groups per unit domain of graphene oxide is significantly increased. Therefore, the hydrophilic domain of graphene oxide is expanded, thereby significantly improving the proton conductivity of the electrolyte membrane 1.

[0056] In addition, since phosphoric acid has very strong acidity, the corrosiveness of phosphoric acid is high. Therefore, when phosphoric acid is directly mixed with the perfluorosulfonic acid ionomer as the ion transfer material 10, phosphoric acid may leach out during the operation of the fuel cell. However, in the present disclosure, phosphoric acid is covalently bonded to graphene oxide and then mixed with the ion transfer material 10, so that the leaching phenomenon does not occur.

[0057] The electrolyte membrane 1 may include 0.01 wt% to 20.0 wt%, preferably 0.1 wt% to 5.0 wt%, and more preferably 0.5 wt% to 2.0 wt% of functionalized graphene oxide 20. If the content of the functionalized graphene oxide 20 is too small, the effect of applying the functionalized graphene oxide 20 cannot be obtained. If the content of the functionalized graphene oxide 20 is too large, meaning that the content of the functionalized graphene oxide 20 is excessively increased, the brittleness of the electrolyte membrane 1 will increase, and the mechanical strength of the electrolyte membrane 1 will decrease.

[0058] Figure 4 is a cross-sectional view of the electrolyte membrane 1 according to another embodiment of the present disclosure. Referring to this figure, the electrolyte membrane 1 may include a porous reinforcing layer 30 and an ion transfer layer 40 provided on at least one surface of the reinforcing layer 30.

[0059] The reinforcing layer 30 increases the mechanical stiffness of the electrolyte membrane 1. The reinforcing layer 30 may be selected from the group including polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (e-PTFE), polyethylene (PE), polypropylene (PP), polyphenylene oxide (PPO), polybenzimidazole (PBI), polyimide (PI), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and combinations thereof. The reinforcing layer 30 may be a porous membrane having a plurality of pores.

[0060] The reinforcing layer 30 may be impregnated with the ion transfer material 10 and the functionalized graphene oxide 20.

[0061] In addition, the ion transfer layer 40 may include the ion transfer material 10 and the functionalized graphene oxide 20 dispersed in the ion transfer material 10.

[0062] The ion transfer material 10 and the functionalized graphene oxide 20 have been previously described, and thus their detailed descriptions will be omitted.

[0063] Figure 5 is a flowchart schematically showing a method of manufacturing a membrane-electrode assembly for a fuel cell according to the present disclosure. Referring to this figure, the method may include: a step (S10) of preparing cerium oxide and phosphoric acid-functionalized graphene oxide (hereinafter referred to as "functionalized graphene oxide"); a step (S20) of mixing the functionalized graphene oxide with an ion transfer material; a step (S30) of manufacturing an electrolyte membrane using the mixture; and a step (S40) of forming electrodes on opposite surfaces of the electrolyte membrane.

[0064] The step (S10) of preparing the functionalized graphene oxide may include: a step (a) of functionalizing graphene oxide with phosphoric acid; and a step (b) of functionalizing graphene oxide with cerium oxide.

[0065] When functionalizing graphene oxide with phosphoric acid and cerium oxide, there is no particular limitation on their order. By appropriately adjusting the starting materials used in each step to be described later, substantially the same results can be obtained regardless of the order. In the present specification, for the sake of convenience of description, graphene oxide is first functionalized with phosphoric acid and then with cerium oxide.

[0066] The step (a) of functionalizing graphene oxide with phosphoric acid may include: a step (a-1) of mixing a phosphoric acid precursor material and graphene oxide to prepare a first mixture; a step (a-2) of introducing an active additive into the first mixture to prepare a second mixture; a step (a-3) of separating the second mixture into a liquid material and a solid material; a step (a-4) of drying the separated solid material to prepare a solid powder; and a step (a-5) of washing the solid powder to obtain phosphoric acid-functionalized graphene oxide. Hereinafter, each step will be described in detail.

[0067] Step (a-1) of preparing the first mixture

[0068] This step is to mix a phosphoric acid precursor material and graphene oxide to prepare a first mixture. The phosphoric acid precursor material is a material for providing phosphoric acid to be functionalized onto graphene oxide, and preferably includes triethyl phosphite (P(OEt)3).

[0069] The first mixture can be prepared by mixing 0.1 to 2.0 parts by weight of graphene oxide with 100 parts by weight of the phosphoric acid precursor material. If the content of graphene oxide is too small, the ratio of phosphoric acid functionalized onto graphene oxide decreases, making it practically difficult to obtain a sufficient phosphoric acid functionalization effect. If the content of graphene oxide is too large, the reaction efficiency decreases.

[0070] Since triethyl phosphite forms hydrocarbon chains with a small volume, triethyl phosphite can be densely functionalized onto the domains of graphene oxide.

[0071] Step (a-2) of preparing the second mixture

[0072] This step is to introduce and disperse an active additive into the first mixture to prepare a second mixture. The active additive is added to activate the oxygen-containing functional groups present on the surface of graphene oxide. After the activation is completed, the oxygen-containing functional groups can easily bond to the phosphoric acid precursor material.

[0073] Preferably, the active additive includes lithium bromide (LiBr).

[0074] Next, based on 100 parts by weight of the phosphoric acid precursor material, 0.1 to 5.0 parts by weight of the active additive can be introduced. If the amount of the active additive introduced is too small, it is difficult to fully activate the oxygen-containing functional groups of graphene oxide. If the amount of the active additive introduced is too large, the activation efficiency decreases.

[0075] Dispersion can be performed alone to uniformly mix the active additive with the first mixture. The dispersion can be sonication and can be carried out for 10 to 120 minutes.

[0076] After dispersing the active additive, preferably, at 80 °C to 120 °C, the second mixture is stirred in a nitrogen (N2) atmosphere for 10 to 50 hours to fully activate the oxygen-containing functional groups of graphene oxide.

[0077] Step (a-3) of separating the second mixture into a liquid material and a solid material

[0078] After stirring the second mixture, the second mixture can be separated into a liquid material and a solid material by centrifugation and filtration, etc. The centrifugation can be carried out at 3000 to 5000 rpm.

[0079] Step (a-4) of preparing the solid powder

[0080] This step is to dry the solid material separated in the previous step to prepare a solid powder. The drying can be carried out at 60 °C to 90 °C for 1 to 24 hours.

[0081] Step (a-5) of obtaining phosphoric acid-functionalized graphene oxide

[0082] This step is to wash the dried solid powder to obtain phosphoric acid-functionalized graphene oxide. Specifically, any one selected from the group consisting of tetrahydrofuran (THF), dimethylformamide (DMF), water, and combinations thereof can be used to wash the solid powder. The washing can be carried out several times. However, the last wash needs to be carried out with water to convert the ethoxy group of triethyl phosphite into a hydroxyl group, so that phosphoric acid-functionalized graphene oxide can be obtained.

[0083] The step (b) of functionalizing graphene oxide with cerium oxide may include: a step (b-1) of mixing a cerium precursor material and graphene oxide to prepare a third mixture; and a step (b-2) of reacting the third mixture to obtain cerium oxide-functionalized graphene oxide. Here, when phosphoric acid-functionalized graphene oxide is used as graphene oxide, cerium oxide and phosphoric acid-functionalized graphene oxide can finally be obtained. Hereinafter, these steps will be described in detail.

[0084] Step (b-1) of preparing the third mixture

[0085] This step is to mix a cerium precursor material and phosphoric acid-functionalized graphene oxide to prepare a third mixture. The cerium precursor material may include cerium nitrate hexahydrate (Ce(NO3)3·6H2O).

[0086] The third mixture can be prepared by mixing 1.0 to 20.0 parts by weight, preferably 2.0 to 10.0 parts by weight, of the cerium precursor material with 100 parts by weight of phosphoric acid-functionalized graphene oxide. If the content of the cerium precursor material is too small, the ratio of functionalized cerium oxide decreases, making it difficult to obtain a sufficient cerium oxide functionalization effect. If the content of the cerium precursor material is too large, the reaction efficiency decreases.

[0087] The cerium precursor material, phosphoric acid-functionalized graphene oxide, and deionized water are uniformly mixed with each other, and then ammonia water can be added to the mixture to control the pH of the third mixture to 9 or more.

[0088] Step (b-2) of obtaining cerium oxide-functionalized graphene oxide

[0089] This step is to react the third mixture to obtain cerium oxide and phosphoric acid-functionalized graphene oxide (or cerium oxide-functionalized graphene oxide). This reaction can be carried out at a high temperature. For example, it can be carried out at 100 °C to 300 °C for 12 to 48 hours.

[0090] Subsequently, the obtained product can be washed and then the solid material can be separated from the obtained product by centrifugation. Washing can be carried out using deionized water and / or ethanol.

[0091] The solid material can be dried at 50 °C to 200 °C for 12 to 48 hours to finally obtain cerium oxide and phosphoric acid-functionalized graphene oxide (or cerium oxide-functionalized graphene oxide).

[0092] The functionalized graphene oxide can be mixed with an ion transfer material (S20), and the mixture can be used to prepare an electrolyte membrane (S30).

[0093] As Figure 2 The electrolyte membrane according to an embodiment of the present disclosure as shown can be manufactured by coating the mixture on a substrate and drying it. At this time, the coating and drying methods are not particularly limited. Using the coating and drying methods commonly used in the fuel cell field is sufficient.

[0094] As Figure 4 The electrolyte membrane according to an embodiment of the present disclosure as shown can be manufactured by performing the following steps: impregnating the mixture into a porous reinforcing layer; and coating the mixture on at least one surface of the reinforcing layer to form an ion transfer layer.

[0095] The reinforcing layer and the ion transfer material have been described previously, and thus their detailed descriptions will be omitted.

[0096] A pair of electrodes can be formed on the opposite surfaces of the electrolyte membrane obtained as described above to obtain a membrane-electrode assembly. The method of forming the electrodes is not particularly limited as long as the method is commonly used in the fuel cell field for manufacturing electrodes.

[0097] Hereinafter, the present disclosure will be described in more detail with reference to specific examples. However, the following examples are only examples for helping to understand the present disclosure, and the present disclosure is not limited by the following examples.

[0098] Manufacturing example

[0099] First, 300 ml of triethyl phosphite (25 °C, 0.969 g / ml) was placed in a round flask, 300 mg of graphene oxide was added, and it was stirred for about 2 hours.

[0100] Subsequently, 800 mg of lithium bromide (LiBr) was added to the graphene oxide dispersion solution, and it was further ultrasonically dispersed for about 60 minutes.

[0101] At 100 °C, the mixed solution was stirred in a nitrogen atmosphere for 48 hours and centrifuged at 4000 rpm to separate the solution into a liquid material and a solid material. Subsequently, the solid powder was dried at 75 °C for about 12 hours.

[0102] The dried powder was washed with a mixture of tetrahydrofuran and dimethylformamide in a 1:1 ratio, and then washed with deionized water to obtain phosphoric acid-functionalized graphene oxide.

[0103] Next, 100 mg of phosphoric acid-functionalized graphene oxide was mixed with 50 ml of deionized water and ultrasonically dispersed for 4 hours. Cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was weighed and added to the dispersion solution such that, based on 100 parts by weight of phosphoric acid-functionalized graphene oxide, it included 5.0 parts by weight of cerium oxide (Examples 1-1 to 1-4) or 10 parts by weight of cerium oxide (Example 2), and stirred to prepare a homogeneous dispersion solution. Subsequently, 4 ml of ammonia water was added to the dispersion solution such that the pH of the dispersion solution was maintained above 9.

[0104] While stirring the dispersion solution, a high-temperature reaction was carried out at 180 °C for about 24 hours. The reaction product was washed with deionized water and ethanol and separated into a liquid material and a solid material by centrifugation. Finally, the separated solid material was dried at 80 °C for about 24 hours to prepare cerium oxide and phosphoric acid-functionalized graphene oxide.

[0105] Examples 1-1 to 1-4 and Example 2

[0106] Using the cerium oxide and phosphoric acid-functionalized graphene oxide obtained according to the production examples, an electrolyte membrane was manufactured under the content conditions shown in Table 1 below.

[0107] Specifically, cerium oxide and phosphoric acid-functionalized graphene oxide were added to a perfluorosulfonic acid ionomer, mixed together with dimethylformamide, and the well-mixed solution was coated on a substrate to manufacture an electrolyte membrane.

[0108] Table 1

[0109]

[0110] 1) is a value based on 100 parts by weight of PGO

[0111] Comparative example

[0112] An electrolyte membrane was manufactured using only a dispersion solution of perfluorosulfonic acid ionomer without adding cerium oxide and phosphoric acid-functionalized graphene oxide.

[0113] Experimental example 1 - Visual evaluation

[0114] Figure 6A 、 Figure 6B 、 Figure 6C and Figure 6D are photographs respectively showing electrolyte membranes manufactured according to Example 1-1, Example 1-2, Example 1-3, and Example 1-4. Referring to these figures, it can be seen that the more the content of cerium oxide and phosphoric acid-functionalized graphene oxide, the darker the color of the electrolyte membrane.

[0115] Experimental example 2 - Hydrogen ion conductivity based on temperature

[0116] Measure the temperature-based hydrogen ion conductivity of electrolyte membranes manufactured according to Example 1-1 to 1-4 and the comparative example. The results are shown in Figure 7 . The hydrogen ion conductivity test is carried out under the conditions of a temperature range of 40 °C to 90 °C and a relative humidity of 100%.

[0117] It can be seen that compared with the comparative example, the electrolyte membranes of Example 1-1 and Example 1-2 exhibit higher hydrogen ion conductivity in the entire temperature range, and in particular, Example 1-2 exhibits the highest conductivity value. On the contrary, it can be seen that compared with the comparative example, Example 1-3 and Example 1-4 with a further increased content of cerium oxide and phosphoric acid-functionalized graphene oxide exhibit lower hydrogen ion conductivity.

[0118] Experimental example 3 - Measurement of fluoride ion emission rate based on time

[0119] Measure the time-based fluoride ion emission rate of electrolyte membranes manufactured according to Example 1-4, Example 2, and the comparative example. The results are shown in Figure 8 . Referring to this figure, it can be seen that compared with the comparative example, the time-based Fluorine Ion emissions of Example 1-4 and Example 2 are much less.

[0120] It is obvious from the foregoing that according to the present disclosure, an electrolyte membrane having improved chemical durability and hydrogen ion conductivity and a membrane-electrode assembly including the electrolyte membrane can be obtained.

[0121] The effects of the present disclosure are not limited to those mentioned above. It should be understood that the effects of the present disclosure include all effects that can be inferred from the foregoing description of the present disclosure.

[0122] The present disclosure has been described in detail with reference to the preferred embodiments of the present disclosure. However, those skilled in the art will understand that these embodiments can be changed without departing from the principles and spirit of the present disclosure, and the scope of the present disclosure is defined by the appended claims and their equivalents.

Claims

1. A membrane - electrode assembly for a fuel cell, the membrane - electrode assembly comprising: An electrolyte membrane; And A pair of electrodes disposed on opposite surfaces of the electrolyte membrane, Wherein the electrolyte membrane comprises cerium oxide and phosphoric acid co - functionalized graphene oxide, Wherein the cerium oxide and phosphoric acid co - functionalized graphene oxide has a structure in which cerium oxide is distributed on the surface of graphene oxide and phosphoric acid is bonded to the oxygen element included in the functional groups of graphene oxide.

2. The membrane-electrode assembly according to claim 1, wherein, The electrolyte membrane comprises perfluorosulfonic acid (PFSA) ionomer.

3. The membrane-electrode assembly according to claim 1, wherein, The electrolyte membrane comprises 0.01 wt% to 20.0 wt% of the co - functionalized graphene oxide.

4. The membrane-electrode assembly according to claim 1, wherein, The electrolyte membrane comprises: A porous reinforcing layer impregnated with an ion transfer material and the co - functionalized graphene oxide; and An ion transfer layer disposed on at least one surface of the reinforcing layer, the ion transfer layer comprising an ion transfer material and the co - functionalized graphene oxide.

5. The membrane-electrode assembly according to claim 4, wherein, The reinforcing layer comprises any one selected from polytetrafluoroethylene, expanded polytetrafluoroethylene, polyethylene, polypropylene, polyphenylene ether, polybenzimidazole, polyimide, polyvinylidene fluoride, polyvinyl chloride, and combinations thereof.

6. A method for manufacturing a membrane - electrode assembly for a fuel cell according to any one of claims 1 - 5, the method comprising: Preparing cerium oxide and phosphoric acid co - functionalized graphene oxide; Mixing the co - functionalized graphene oxide with an ion transfer material; Manufacturing an electrolyte membrane using the mixture; And Forming electrodes on opposite surfaces of the electrolyte membrane.

7. The method according to claim 6, wherein Preparing the co - functionalized graphene oxide comprises: (a) Functionalizing graphene oxide with phosphoric acid; and (b) Functionalizing graphene oxide with cerium oxide.

8. The method according to claim 7, wherein, Functionalizing graphene oxide with phosphoric acid comprises: Mixing a phosphoric acid precursor material and graphene oxide to prepare a first mixture; Adding an active additive to the first mixture to prepare a second mixture; Separating the second mixture into a liquid material and a solid material; Drying the separated solid material to prepare a solid powder; and Washing the solid powder to obtain phosphoric acid - functionalized graphene oxide.

9. The method according to claim 7, wherein, Functionalizing graphene oxide with cerium oxide comprises: Mixing a cerium precursor material and graphene oxide to prepare a third mixture; and Reacting the third mixture to obtain cerium oxide - functionalized graphene oxide.

10. The method according to claim 8, wherein The phosphoric acid precursor material comprises triethyl phosphite P(OEt)3.

11. The method according to claim 8, wherein, The first mixture is prepared by mixing 100 parts by weight of the phosphoric acid precursor material with 0.1 - 2.0 parts by weight of the graphene oxide.

12. The method according to claim 8, wherein The active additive comprises lithium bromide (LiBr).

13. The method according to claim 8, wherein, Based on 100 parts by weight of the phosphoric acid precursor material, 0.1 - 5.0 parts by weight of the active additive is added.

14. The method according to claim 9, wherein, The cerium precursor material comprises cerium nitrate hexahydrate Ce(NO3)3·6H2O.

15. The method according to claim 9, wherein, The third mixture is prepared by mixing 100 parts by weight of the graphene oxide with 1.0 - 20.0 parts by weight of the cerium precursor material.

16. The method according to claim 6, wherein, Manufacturing the electrolyte membrane comprises: Coating the mixture on a substrate.

17. The method according to claim 6, wherein Manufacturing the electrolyte membrane comprises: Impregnating the mixture into a porous reinforcing layer; and Apply the mixture on at least one surface of the reinforcing layer.

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