Porous multi-metal oxide nanotubes and preparation method thereof

Abstract

Disclosed are porous polymetallic oxide nanotubes and a method for preparing the same. In one aspect, a method for preparing porous polymetallic oxide nanotubes is provided, which includes: (a) preparing a mixture including a metal-acetylacetonate precursor, polyacrylonitrile (PAN), and a solvent component; and (b) preparing a nanocomposite from the mixture, wherein the metal of the metal-acetylacetonate precursor includes non-radioactive alkali metal stable isotopes and non-radioactive alkaline earth metal stable isotopes. Thus, porous polymetallic oxide nanotubes having a single-phase multivalence can be obtained in high yield without using harmful chemicals. In addition, a polymer electrolyte membrane including the porous polymetallic oxide nanotubes can maintain and improve mechanical strength and thus can maintain durability even during battery operation, and can have improved proton conductivity even at low humidity. A fuel cell including the polymer electrolyte membrane can have improved performance.

Description

Technical Field

[0001] The present invention relates to porous multi-metal oxide nanotubes and a method for preparing the same. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) have received attention as an alternative energy source to fossil fuels because they have a high energy conversion efficiency of 60% or higher, zero emissions, a high current density, are lightweight, and can operate at low working temperatures.

[0003] Meanwhile, in a proton exchange membrane fuel cell (PEMFC), Pt / C is mainly used as a catalyst for the oxygen reduction reaction (ORR) at the positive electrode, while the hydrogen oxidation reaction (HOR) occurs at the negative electrode. In particular, since the ORR at the positive electrode is slower than the HOR at the negative electrode, the rate of the ORR determines the performance of the entire fuel cell system. At this time, if the proton exchange membrane fuel cell (PEMFC) can be advantageously alleviated from flooding even when operating under low relative humidity conditions. However, the proton conductivity of Nafion ionomer varies greatly at low humidity.

[0004] To solve this problem, research has been conducted to increase the water content by incorporating nanoscale hygroscopic metal oxide particles. However, in this case, the problem is that the antioxidant itself aggregates and precipitates during battery operation, resulting in a significant decrease in battery stability, and the proton conductivity is still very low at low humidity.

[0005] Meanwhile, when the fuel cell operates in an acidic environment with a pH of 2 or lower, hydrogen peroxide (H2O2) is generated during the catalytic reaction to form free radicals. Therefore, the formed free radicals attack the electrolyte membrane structure and reduce the performance of the fuel cell. To remove the formed free radicals, research has been conducted to introduce antioxidants based on organic / metal compounds or inorganic substances into the electrolyte membrane of the fuel cell. However, in this case, there is a disadvantage that the antioxidant can leak from the membrane electrode assembly (MEA) during the long-term operation of the fuel cell and can also reduce the proton conductivity.

[0006] Therefore, there is a need to develop a technology that can improve the performance of a proton exchange membrane fuel cell (PEMFC) by increasing the proton conductivity, which is reduced due to free radicals and low humidity generated during the operation of the PEMFC. Summary of the Invention

[0007] In a preferred aspect, a method for preparing porous polymetallic oxide nanotubes from at least two metal-acetylacetonate precursors, a polymer electrolyte membrane and an electrode each including the porous polymetallic oxide nanotubes, and a fuel cell including the porous polymetallic oxide nanotubes are provided. The porous polymetallic oxide nanotubes are prepared by the method described herein and include a multivalent polymetallic oxide having a single phase.

[0008] The object of the present invention is not limited to the above object. The object of the present invention will become clearer through the following description and will be achieved by the means described in the appended claims and their combinations.

[0009] In one aspect, a method for preparing porous polymetallic oxide nanotubes is provided, including: (a) preparing a mixture including a metal-acetylacetonate precursor, polyacrylonitrile (PAN), and a solvent component; and (b) preparing a nanocomposite from the mixture; wherein the metal of the metal-acetylacetonate precursor includes non-radioactive alkali metal stable isotopes and non-radioactive alkaline earth metal stable isotopes. Suitably, preparing the nanocomposite may include electrospinning the mixture. In certain preferred aspects, the method may further include calcining the nanocomposite.

[0010] In one aspect, a method for preparing porous polymetallic oxide nanotubes is provided. The method may include: preparing a spinning solution including a metal-acetylacetonate precursor, polyacrylonitrile (PAN), and a solvent component; preparing a nanocomposite by electrospinning the spinning solution; and calcining the nanocomposite. Preferably, the metal included in the metal-acetylacetonate precursor includes non-radioactive alkali metal stable isotopes and non-radioactive alkaline earth metal stable isotopes.

[0011] The non-radioactive alkali metal stable isotopes may include one or more selected from the following: titanium (Ti), cerium (Ce), strontium (Sr), lanthanum (La), gadolinium (Gd), erbium (Er), scandium (Sc), palladium (Pd), osmium (Os), dysprosium (Dy), ytterbium (Yb), indium (In), and neodymium (Nd), and the non-radioactive alkaline earth metal stable isotopes may include one or more selected from the following: zirconium (Zr), niobium (Nb), yttrium (Y), tantalum (Ta), vanadium (V), molybdenum (Mo), silicon (Si), ruthenium (Ru), tin (Sn), tungsten (W), uranium (U), seaborgium (Sg), and tellurium (Te).

[0012] The metal-acetylacetonate precursor may include two or more precursors selected from the following: titanium(IV) acetylacetonate (Ti) precursor, zirconium(IV) acetylacetonate (Zr) precursor, cerium(III) acetylacetonate (Ce) precursor, neodymium(IV) acetylacetonate (Nd) precursor, gadolinium(III) acetylacetonate (Gd) precursor, vanadyl acetylacetonate (VO(C5H7O2)2) precursor, tantalum(V) acetylacetonate (Ta) precursor, niobium(V) acetylacetonate (Nb) precursor, strontium acetylacetonate (Sr) precursor, palladium(II) acetylacetonate (Pd) precursor, and yttrium(III) acetylacetonate (Y) precursor.

[0013] Based on 100 parts by weight of polyacrylonitrile (PAN), the content of the metal-acetylacetonate precursor may be about 10 to 50 parts by weight.

[0014] Electrospinning can be carried out by an electrospinning device. The distance between the spinneret and the collector in the electrospinning device can be about 8 to 12 cm, the high-voltage power in the electrospinning is about 15 to 22 kV, and the volume flow rate during electrospinning can be about 0.8 to 1 mL / h -1 , the rotation speed of the spinning solution can be about 300 to 1000 rpm, and electrospinning can be carried out in an ambient air atmosphere.

[0015] The calcination step can be carried out by calcining the nanocomposite at a temperature higher than about 400 °C to not higher than about 600 °C for about 1 to 5 hours.

[0016] The heating rate during calcination in the calcination step can be about 4 to 6 °C / minute.

[0017] The calcination step may include stabilizing the nanocomposite at a temperature of about 230 °C to 250 °C for about 0.5 to 1.5 hours before calcining the nanocomposite.

[0018] In one aspect, there is also provided that the porous multi-metal oxide nanotube may include a multi-metal oxide represented by the following formula and having a single-phase multivalence.

[0019] [Formula]

[0020] A2B2O8

[0021] Wherein A is a non-radioactive alkali metal stable isotope ion and B is a non-radioactive alkaline earth metal stable isotope ion.

[0022] Non-radioactive alkali metal stable isotope ions may include ions of one or more metals selected from: titanium (Ti), cerium (Ce), strontium (Sr), lanthanum (La), gadolinium (Gd), erbium (Er), scandium (Sc), palladium (Pd), osmium (Os), dysprosium (Dy), ytterbium (Yb), indium (In), and neodymium (Nd), and non-radioactive alkaline earth metal stable isotope ions may include ions of at least one selected from: zirconium (Zr), niobium (Nb), yttrium (Y), tantalum (Ta), vanadium (V), molybdenum (Mo), silicon (Si), ruthenium (Ru), tin (Sn), tungsten (W), uranium (U), seaborgium (Sg), and tellurium (Te).

[0023] The polymetallic oxide may have a fluorite crystal structure, a pyrochlore crystal structure, or a mixed crystal structure thereof.

[0024] The polymetallic oxide may have a single-phase orthorhombic form.

[0025] The A-ion radius / B-ion radius ratio of the polymetallic oxide may be from about 0.7 to 1.1.

[0026] The average pore diameter of the porous polymetallic oxide nanotubes may be from about 10 to 20 nm.

[0027] In one aspect, there is provided a polymer electrolyte membrane that may include an ion conductor within the pores of a nanonet including porous polymetallic oxide nanotubes.

[0028] Based on the total weight of the polymer electrolyte membrane of 100 wt%, the content of the porous polymetallic oxide nanotubes may be from about 0.5 to 1.5 wt%.

[0029] There is also provided an electrode that may include the porous polymetallic oxide nanotubes as described herein and a binder.

[0030] Based on the sum of 100 wt% of the polymetallic oxide nanotubes and the binder, the content of the porous polymetallic oxide nanotubes may be from about 0.5 to 1.5 wt%.

[0031] There is also provided a fuel cell including the polymer electrolyte membrane as described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments shown in the accompanying drawings, which are given by way of example only and thus are not limiting of the present invention, and wherein:

[0033] Figure 1 An exemplary method for preparing porous polymetallic oxide nanotubes according to an exemplary embodiment of the present invention is shown;

[0034] Figure 2A and 2B are SEM images of exemplary Ti2Zr2O8 multi-nanotubes (TZONT) ( Figure 2A : magnification of 45,000×, Figure 2B : magnification of 80,000×);

[0035] Figure 3A and 3B are SEM images of an exemplary polymer electrolyte membrane (Nafion-TZONT membrane) prepared using Ti2Zr2O8 multi-nanotubes (TZONT) ( Figure 3A : magnification of 1,100×, Figure 3B : magnification of 8,000×);

[0036] Figure 4A is an XRD pattern obtained by performing X-ray diffraction analysis to analyze the Ti2Zr2O8 multi-nanotubes (TZONT) prepared in Preparation Example 1;

[0037] Figure 4B shows the lattice structure of the Ti2Zr2O8 multi-nanotubes (TZONT);

[0038] Figure 5 is a graph showing the evaluation results of the proton conductivity of exemplary polymer electrolyte membranes according to Example 1 and Comparative Examples 1 to 5;

[0039] Figure 6 is a graph showing the evaluation results of tensile tests performed on exemplary polymer electrolyte membranes according to Example 1 and Comparative Examples 1 to 5;

[0040] Figure 7A and 7B are graphs showing the cell voltage and power density versus current density of fuel cells according to Example 3 in which Ti2Zr2O8 multi-nanotubes (TZONT) are only applied to the polymer electrolyte membrane and Comparative Examples 6 to 10 ( Figure 7A : 100% RH; and Figure 7B : 20% RH);

[0041] Figure 8A and 8B are graphs showing the cell voltage and power density versus current density of fuel cells according to Example 4 in which Ti2Zr2O8 multi-nanotubes (TZONT) are applied to the positive electrode and Comparative Example 11 ( Figure 8A : 100% RH; and Figure 8B : 20% RH);

[0042] Figure 9A and 9Bis a graph showing the fluoride release rate (FER) values of the negative electrode (anode) side ( Figure 9A ) of the polymer electrolyte membrane and the fluoride release rate (FER) values of the positive electrode (cathode) side ( Figure 9B ) in the open circuit voltage (OCV) holding test of the fuel cell according to Example 3 and Comparative Example 6; and

[0043] Figure 10 is a graph showing the time-dependent results of the open circuit voltage (OCV) holding test of the fuel cell of Example 3 under the temperature condition of 80 °C and the humidity condition of 20% RH. Detailed Description

[0044] The above objects, other objects, features, and advantages of the present invention will become apparent from the following embodiments described in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be implemented in many different forms. On the contrary, these embodiments disclosed herein are provided to make the present invention thorough and complete and to fully convey the spirit of the present invention to those skilled in the art.

[0045] In this specification, it should be understood that terms such as "including" and "having" are intended to indicate the presence of the mentioned features, quantities, steps, operations, components, parts, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts, or combinations thereof. In addition, when a part such as a layer, film, region, plate, etc. is referred to as being "on" or "above" another part, it refers not only to the case where the part is directly above the other part, but also to the case where there is a third part therebetween. On the contrary, when a part, when a part such as a layer, film, region, plate, etc. is referred to as being "under" another part, it refers not only to the case where the part is directly under the other part, but also to the case where there is a third part therebetween.

[0046] Since all numbers, numerical values, and / or representations of component amounts, reaction conditions, polymer compositions, and mixtures used in this specification are affected by various measurement uncertainties encountered in obtaining such numerical values, all such values should be understood to be modified in all instances by the term "about" unless otherwise indicated. Where a numerical range is disclosed herein, unless otherwise indicated, such range is continuous, including the minimum and maximum values of the range and each value therebetween. Further, unless otherwise indicated, when a range refers to integers, each integer between the minimum and maximum values of such range is included. Additionally, unless specifically stated or obvious from the context, as used herein, the term "about" is understood to be within the normal tolerances in the art, e.g., within 2 standard deviations of the mean value. "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 a stated value. Unless the context clearly indicates otherwise, all numerical values provided herein are modified by the term "about".

[0047] In this specification, when a range is stated for a parameter, it should be understood that the parameter includes all values within the stated range, including the endpoints of the stated range. For example, a range of 5 to 10 will be understood to include the values 5, 6, 7, 8, 9, and 10, as well as any subranges, such as 6 to 10, 7 to 10, 6 to 9, and 7 to 9, and also includes any values and ranges between reasonable integers within the context of the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. For example, a range of "10% to 30%" will be understood to include the values 10%, 11%, 12%, 13%, etc., and all integers up to and including 30%, as well as any subranges, such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and also includes any values between reasonable integers within the stated range, such as 10.5%, 15.5%, 25.5%, etc.

[0048] Fuel cell technologies are provided that improve fuel cell performance by increasing proton conductivity even at low humidity. For example, methods for preparing porous multi-metal oxide nanotubes are particularly provided herein. When the porous multi-metal oxide nanotubes prepared using at least two metal-acetylacetonate precursors under specific conditions satisfy a mixed crystal structure of a single-phase multivalent, orthorhombic single-phase pyrochlore crystal structure and a fluorite crystal structure, a polymer electrolyte membrane including the porous multi-metal oxide nanotubes can have high proton conductivity under low humidity conditions and its mechanical properties can also be maintained.

[0049] Figure 1It is a schematic diagram showing a method for preparing porous multi-metal oxide nanotubes according to an exemplary embodiment of the present invention. The method includes the following steps: (S10) preparing a spinning solution containing at least two metal-acetylacetonate precursors, polyacrylonitrile (PAN), and a solvent component; (S20) preparing a nanocomposite by electrospinning the spinning solution; and (S30) calcining the nanocomposite.

[0050] The step (S10) of preparing the spinning solution includes the step of preparing the spinning solution by mixing at least two metal-acetylacetonate precursors, polyacrylonitrile (PAN), and a solvent component.

[0051] The metals included in the at least two metal-acetylacetonate precursors may include non-radioactive alkali metal stable isotopes and non-radioactive alkaline earth metal stable isotopes. Preferably, the non-radioactive alkali metal stable isotopes may include one or more selected from the following: titanium (Ti), cerium (Ce), strontium (Sr), lanthanum (La), gadolinium (Gd), erbium (Er), scandium (Sc), palladium (Pd), osmium (Os), dysprosium (Dy), ytterbium (Yb), indium (In), and neodymium (Nd), and the non-radioactive alkaline earth metal stable isotopes may include at least one selected from the following: zirconium (Zr), niobium (Nb), yttrium (Y), tantalum (Ta), vanadium (V), molybdenum (Mo), silicon (Si), ruthenium (Ru), tin (Sn), tungsten (W), uranium (U), seaborgium (Sg), and tellurium (Te).

[0052] Therefore, the at least two metal-acetylacetonate precursors may include one or more precursors selected from the following: titanium(IV) acetylacetonate precursor, zirconium(IV) acetylacetonate precursor, cerium(III) acetylacetonate precursor, neodymium(IV) acetylacetonate precursor, gadolinium(III) acetylacetonate precursor, vanadyl acetylacetonate (VO(C5H7O2)2) precursor, tantalum(V) acetylacetonate precursor, niobium(V) acetylacetonate precursor, strontium acetylacetonate precursor, palladium(II) acetylacetonate precursor, and yttrium(III) acetylacetonate precursor.

[0053] Preferably, at least two metal-acetylacetonate precursors may include titanium(IV) acetylacetonate oxide (Ti) and zirconium(IV) acetylacetonate (Zr) to provide a more controllable reaction rate in the synthesis of metal oxide nanostructures. For example, titanium(IV) acetylacetonate oxide (Ti) and zirconium(IV) acetylacetonate (Zr) may have stronger ligand coordination and may be less prone to hydrolysis, which is a common drawback of other precursors (due to their low water stability), and when using an oxygen-containing polar solvent, titanium(IV) acetylacetonate oxide (Ti) and zirconium(IV) acetylacetonate (Zr) can be easily synthesized into metal oxide nanostructures by heating. More preferably, the molar ratio of titanium(IV) acetylacetonate oxide (Ti):zirconium(IV) acetylacetonate (Zr) may be about 1:1 to 1.4, and even more preferably about 1:1.2. When the molar ratio is too low outside the above range, there is a problem that the viscosity of the spinning solution is too low to perform electrospinning, and when the molar ratio is too high, there is a problem that it is impossible to obtain a single-phase porous multi-metal oxide nanotube.

[0054] The spinning solution can be prepared by mixing and stirring a solution containing at least two metal-acetylacetonate precursors dissolved therein and a solution containing a polymer. Based on 100 parts by weight of the polymer, the content of the metal-acetylacetonate precursor in the spinning solution may be about 10 to 50 parts by weight, particularly about 10 to 30 parts by weight. When the content of at least two metal-acetylacetonate precursors is too high outside the above range, there is a problem that the diameter of the nanotubes increases excessively, reducing the surface area of the nanotubes, and when the content of the precursor is too low, there is a problem of reduced nanotube yield.

[0055] As the polymer, polyacrylonitrile (PAN) can be used, but the polymer is not limited thereto. The weight-average molecular weight of the polymer may be about 120,000 to 180,000.

[0056] The step of preparing the nanocomposite (S20) is a step of preparing the nanocomposite by electrospinning the spinning solution prepared in step S10.

[0057] Electrospinning can be carried out by any conventional method applicable to the present invention. For example, the spinning solution can be spun by, for example, electrospray and electrospinning. As a more specific example, the nanocomposite can be prepared by an electrospray or electrospinning device including a syringe having about 5 mL and / or about 10 mL NORM-JECT@ and a 22G metal nozzle.

[0058] The distance between the spinneret and the collector in the electrospinning device for electrospinning can be about 8 to 12 cm, the high-voltage power in electrospinning can be about 15 to 22 kV, and the volume flow rate during electrospinning can be about 0.8 to 1 mL / h -1, the rotational speed of the spinning solution can be about 300 to 1000 rpm. In addition, electrospinning can be carried out in an ambient air atmosphere. More preferably, electrospinning can be carried out under conditions of about 20 to 25 °C and less than about 30% RH.

[0059] The calcination step (S30) includes the step of calcining the nanocomposite prepared in the calcination step (S20).

[0060] The electrospun nanocomposite can be calcined at a temperature higher than about 400 °C to not higher than about 600 °C for about 1 to 5 hours. In particular, the nanocomposite can be calcined at a temperature higher than about 400 °C to not higher than about 500 °C.

[0061] Thus, since the nanotubes are doped with nitrogen during calcination, the nanotubes have high electron transport ability and can increase the effect of the photoelectric conversion characteristics.

[0062] When the nanocomposite is calcined within the above temperature range, the average diameter of the porous metal oxide nanotubes can be easily adjusted. In particular, porous metal oxide nanotubes having a tubular hollow structure with an average outer diameter of about 80 to 100 nm and an average inner diameter of about 10 to 20 nm can be obtained.

[0063] The heating rate during calcination in the calcination step can be about 4 to 6 °C / min, especially about 5 °C / min. Preferably, before the calcination reaction, the electrospun nanocomposite can be stabilized at a temperature of about 230 to 250 °C for about 0.5 to 1.5 hours, especially about 1 hour.

[0064] Calcination can be carried out in any atmosphere including air, argon (Ar), nitrogen (N2), and / or oxygen (O2).

[0065] After forming the polymetal oxide clusters through the calcination process, the carbon in the clusters can be decomposed as the temperature further increases, thereby preparing hollow porous metal oxide nanotubes.

[0066] The porous polymetal oxide nanotubes can be prepared by the above preparation method and include a polymetal oxide represented by the following formula and having a single-phase multivalence.

[0067] [Formula]

[0068] A2B2O8

[0069] Where A is a non-radioactive alkali metal stable isotope ion and B is a non-radioactive alkaline earth metal stable isotope ion.

[0070] Since the porous polymetallic oxide in the porous polymetallic oxide nanotube includes ions A and ions B uniformly distributed therein, the single phase of the polymetallic oxide can be orthorhombic. Since the porous polymetallic oxide has a single-phase multivalence, it is characterized in that a larger amount of redox reactions occur due to the multivalent transition of each cation and the activation energy of oxide ion diffusion is reduced.

[0071] In addition, the polymetallic oxide can have a fluorite crystal structure, a pyrochlore crystal structure, or a mixed crystal structure thereof. Preferably, the crystal structure of the polymetallic oxide can be a mixed crystal structure of a fluorite crystal structure and a pyrochlore crystal structure. Its crystal structure can be a mixed crystal structure based on the fluorite crystal structure and also includes a crystal structure similar to the pyrochlore crystal structure, and thus the polymetallic oxide is characterized by excellent oxygen storage and release properties because a large number of large voids are ensured in its crystal structure when the phase of the polymetallic oxide is stable.

[0072] Therefore, a polymer electrolyte membrane prepared to include a nanonet of porous polymetallic oxide nanotubes containing a porous polymetallic oxide that satisfies the single-phase multivalence and crystal structure characteristics can have improved mechanical properties or chemical properties such as proton conductivity.

[0073] The polymetallic oxide contained in the porous polymetallic oxide nanotube can be an oxide of one or more metals selected from the following: titanium (Ti), cerium (Ce), strontium (Sr), lanthanum (La), gadolinium (Gd), erbium (Er), scandium (Sc), palladium (Pd), osmium (Os), dysprosium (Dy), ytterbium (Yb), indium (In), and neodymium (Nd), the ions are non-radioactive alkali metal stable isotope ions A of the above formula, and ions of at least one selected from the following: zirconium (Zr), niobium (Nb), yttrium (Y), tantalum (Ta), vanadium (V), molybdenum (Mo), silicon (Si), ruthenium (Ru), tin (Sn), tungsten (W), uranium (U), seaborgium (Sg), and tellurium (Te), the ions are non-radioactive alkaline earth metal stable isotope ions B of the above formula.

[0074] Preferably, the polymetallic oxide can be an oxide having an A-ion radius / B-ion radius ratio of about 0.7 to 1.1. When the radius ratio is too low outside the above range, there are disadvantages such as a reduction in the structural hardness of the polymetallic oxide or a transformation of the fluorite crystal structure, which is one of the crystal structures, into a crystal structure different from those in the present invention. When the radius ratio is too high outside the above range, there are disadvantages such as an increase in the structural hardness of the polymetallic oxide or the non-formation of the fluorite crystal structure. In particular, the polymetallic oxide can include Ti2Zr2O8, which is highly resistant to antioxidant radical attack, can be well dispersed in the polymer electrolyte membrane, and can be used as a catalyst under acidic / alkaline conditions.

[0075] Porous multi-metal oxide nanotubes can be obtained to have a hollow structure with an average outer diameter of about 80 to 100 nm and an average inner diameter of about 10 to 20 nm. In particular, the average pore diameter of the porous multi-metal oxide nanotubes can be about 10 to 20 nm. When the average pore diameter is too small outside the above range, there are the following disadvantages: the ion selectivity of the porous multi-metal oxide nanotubes decreases, the path for transporting reactants is uneven, and the diffusion length to the active sites is extended, resulting in an increase in transport resistance. When the average pore diameter is too large, there are the following disadvantages: the volume density and ion selectivity of the nanotubes decrease, their crossability is high, and their surface area decreases, resulting in a reduction in active / anchoring sites.

[0076] A filler for an electrolyte membrane is also provided, which can include porous multi-metal oxide nanotubes. Since the filler can include porous multi-metal oxide nanotubes, preferably porous TNT (which includes multi-metal oxides, preferably Ti2Zr2O8), it can maintain a high moisture content at temperatures above about 100 °C and / or low humidity. For example, even under conditions of a temperature of about 100 to 110 °C and a humidity of about 18% RH or lower, the filler can maintain a high moisture content.

[0077] A polymer electrolyte membrane for a fuel cell is also provided. The polymer electrolyte membrane can include: a nanonet containing porous multi-metal oxide nanotubes as a filler; and an ion conductor contained in the pores of the nanonet. An electrode is also provided, which includes: porous multi-metal oxide nanotubes as a filler; and a binder.

[0078] At this time, based on the total weight of the polymer electrolyte membrane of 100 wt%, the content of the porous multi-metal oxide nanotubes in the polymer electrolyte membrane can be about 0.5 to 1.5 wt%, and based on the total of 100 wt% of the multi-metal oxide nanotubes and the binder, the content of the porous multi-metal oxide nanotubes in the electrode can be about 0.5 to 1.5 wt%. When the content of the nanotubes is too low outside the above range, there is a disadvantage that the active sites in the catalyst layer are reduced, resulting in a decrease in the performance of the fuel cell. When the content of the nanotubes is too high outside the above range, there is a disadvantage that the nanotubes can aggregate and thus the mass transfer in the catalyst layer may not be smooth.

[0079] In particular, the porous multi-metal oxide nanotubes can increase the proton reduction ability of the polymer electrolyte membrane or the electrode, and thus provide a fuel cell with excellent current density and excellent proton conductivity even at high temperatures and low humidity.

[0080] Examples

[0081] Hereinafter, the present invention will be described in more detail with reference to preparation examples and examples. The following examples are only for helping to understand the present invention, and the scope of the present invention is not limited thereto.

[0082] Preparation Example: Preparation of Ti2Zr2O8 multi-nanotubes (TZONT) as porous multi-metal oxide nanotubes

[0083] (S10) At a temperature of 90 °C, titanium(IV) acetylacetonate oxide (TiOacac) and zirconium(IV) acetylacetonate (Zracac) as at least two metal-acetylacetonate precursors were dissolved in 3.00 g of N,N-dimethylformamide (DMF) as a solvent at a molar ratio of 1:1.2. In addition, at a temperature of 90 °C, 1.00 g of polyacrylonitrile (PAN, Mw = 150,000 g / mol) was completely dissolved in 6.00 g of DMF. The TiOacac-Zracac solution and the PAN solution were mixed together and stirred at 90 °C until a clear and homogeneous solution was observed.

[0084] (S20) Electrospinning was performed on the resulting solution to prepare a nonwoven mat. Specifically, the moving distance between the spinneret and the collector was 10 cm, the high-voltage power of electrospinning was 15 kV, and the volume flow rate during electrospinning was 1.0 mL / h -1 , and the rotational speed of the roller for collecting the mat was 300 rpm. In addition, during electrospinning, the humidity was less than 30% RH and the temperature was 20 to 25 °C. Thus, a PAN / TiOacac-Zracac composite nonwoven mat was prepared.

[0085] (S30) The electrospun PAN / TiOacac-Zracac composite nonwoven mat was stabilized at 250 °C for 1 hour to remove organic substances, and then calcined at 600 °C for 3 hours to prepare Ti2Zr2O8 multi-nanotubes (TZONT). The heating rate during calcination was 5 °C per minute.

[0086] The yield of the Ti2Zr2O8 multi-nanotubes (TZONT) product obtained after calcination was 28 wt%.

[0087] Figure 2A and 2B are SEM images of the Ti2Zr2O8 multi-nanotubes (TZONT), and it can be confirmed that the Ti2Zr2O8 multi-nanotubes (TZONT) prepared according to the preparation example are in the form of tubes with various lengths.

[0088] Example 1: Preparation of a polymer electrolyte membrane for a fuel cell using Ti2Zr2O8 multi-nanotubes (TZONT)

[0089] The Ti2Zr2O8 multi-nanotubes (TZONT) prepared in the preparation examples and 0.5 to 1.5 wt% Nafion ionomer were stirred using an ultrasonic cleaner and a stirrer until a homogeneous mixture was obtained. The mixture was poured into a Petri dish and then dried in a vacuum oven at temperatures of 50, 60, 70, and 80 °C for 2 hours. The prepared electrolyte membrane was separated from the Petri dish and dried at a temperature of 100 °C for 4 hours, thereby preparing a proton transport channel and a polymer electrolyte membrane (Nafion-TZONT membrane) containing the proton transport channel. The average thickness of the prepared polymer electrolyte membrane was about 50 ± 5 μm, and the polymer electrolyte membrane prepared using the Ti2Zr2O8 multi-nanotubes (TZONT) prepared in the preparation examples was treated successively with 5% hydrogen peroxide, water, 0.5 M sulfuric acid, and water for 1 hour each when heated.

[0090] After preparation, the content of Ti2Zr2O8 multi-nanotubes (TZONT) was 1 wt% of the total weight of the polymer electrolyte membrane.

[0091] Figure 3A and 3B is the SEM image of the polymer electrolyte membrane (Nafion-TZONT membrane) prepared using Ti2Zr2O8 multi-nanotubes (TZONT), and it can be confirmed that the Ti2Zr2O8 multi-nanotubes (TZONT) are uniformly dispersed in the Nafion-TZONT membrane.

[0092] Example 2: Preparation of a fuel cell electrode (positive electrode) using Ti2Zr2O8 multi-nanotubes (TZONT)

[0093] Based on the solid content of the binder in the binder solution (5 wt% Nafion perfluororesin solution), 0.5, 1.0, and 1.5 wt% of Ti2Zr2O8 multi-nanotubes (TZONT) were introduced and mixed with the binder solution, and then ultrasonic treatment was carried out for 1 hour. Thereafter, the mixture was stirred at room temperature for 8 hours to prepare an electrode mixture solution. Then, the electrode mixture solution was mixed with Pt / C using deionized (DI) water and isopropyl alcohol (IPA) as solvents to prepare an electrode paste. The gas diffusion layer was coated with the electrode paste to prepare an electrode.

[0094] After preparation, based on the sum of 100 wt% of the metal oxide nanotubes and the binder, the content of Ti2Zr2O8 multi-nanotubes (TZONT) was 1 wt%.

[0095] Example 3: Preparation of a fuel cell including a polymer electrolyte membrane for a fuel cell As the polymer electrolyte membrane, the polymer electrolyte membrane (Nafion-TZONT membrane) prepared in Example 1 was used. Both the positive electrode and the negative electrode were made of Pt / C and a binder. To achieve faster mass transfer and ORR reaction, a binder (Nafion) in an amount of 10 to 30 wt% (based on the weight of Pt / C, calculated as solids) was added only to the positive electrode side. To achieve a fast HOR reaction, a binder (Nafion) in an amount of 10 to 30 wt% (based on the weight of Pt / C, calculated as solids) was added to the negative electrode.

[0096] Example 4: Preparation of a fuel cell including a polymer electrolyte membrane and electrodes for a fuel cell

[0097] As the polymer electrolyte membrane, the polymer electrolyte membrane (Nafion-TZONT membrane) prepared in Example 1 was used, and as the positive electrode, the electrode prepared in Example 2 was used, and as the negative electrode, the negative electrode used in Example 3 was used.

[0098] Comparative Examples 1 to 5: Preparation of a polymer electrolyte membrane for a fuel cell using single nanotubes or nanoparticles

[0099] The polymer electrolyte membrane for a fuel cell was prepared in the same manner as in Example 1, except that: only Nafion was used instead of the polymer electrolyte membrane prepared with the Ti2Zr2O8 multi-nanotubes (TZONT) prepared in Example 1 (Comparative Example 1); a polymer electrolyte membrane (Nafion-TONT membrane; Comparative Example 2) was prepared using porous titanium dioxide (TiO2) nanotubes instead of Ti2Zr2O8 multi-nanotubes (TZONT); a polymer electrolyte membrane (Nafion-ZONT membrane; Comparative Example 3) was prepared using porous zirconium dioxide (ZrO2) nanotubes instead of Ti2Zr2O8 multi-nanotubes (TZONT); a polymer electrolyte membrane (Nafion-CeNT membrane; Comparative Example 4) was prepared using porous cerium dioxide (CeO2) nanotubes instead of Ti2Zr2O8 multi-nanotubes (TZONT); and a polymer electrolyte membrane (Nafion-CeNP membrane; Comparative Example 5) was prepared using porous cerium dioxide (CeO2) nanoparticles instead of Ti2Zr2O8 multi-nanotubes (TZONT).

[0100] Comparative Examples 6 to 11: Preparation of a fuel cell

[0101] A fuel cell was prepared in the same manner as in Example 3, except that: a fuel cell prepared using the polymer electrolyte membrane for fuel cells prepared in Comparative Example 1 (Comparative Example 6); a fuel cell prepared using the polymer electrolyte membrane for fuel cells prepared in Comparative Example 2 (Comparative Example 7), a fuel cell prepared using the polymer electrolyte membrane for fuel cells prepared in Comparative Example 3 (Comparative Example 8), a fuel cell prepared using the polymer electrolyte membrane for fuel cells prepared in Comparative Example 4 (Comparative Example 9), a fuel cell prepared using the polymer electrolyte membrane for fuel cells prepared in Comparative Example 5 (Comparative Example 10).

[0102] In addition, a fuel cell (Comparative Example 11) was prepared in the same manner as in Example 4, except that the polymer electrolyte membrane for fuel cells prepared in Comparative Example 1 was used.

[0103] Experimental Example 1: Evaluation of the crystal phase of Ti2Zr2O8 multi-nanotubes (TZONT) as porous multi-metal oxide nanotubes

[0104] Figure 4A is an XRD pattern obtained by performing X-ray diffraction analysis to analyze the crystal phase of the Ti2Zr2O8 multi-nanotubes (TZONT) prepared in Preparation Example 1. Figure 4B Shows the lattice structure of the Ti2Zr2O8 multi-nanotubes (TZONT).

[0105] As Figure 4A shown, it can be confirmed that the XRD pattern according to the standard XRD database (ICDD: 00-034-0415) is consistent with Ti2Zr2O8. As Figure 4B shown, it can be confirmed that the lattice structure of the multi-metal oxide Ti2Zr2O8 (TZO) shown in the reference Figure 4A XRD pattern has two formula units in a unit cell with the space group Pbcn (60), and the lattice parameters are and and the ad statistic is 0.23026, and the density of TZO is 5.1546 g cm -3 .

[0106] That is, it can be confirmed that the titanium and zirconium elements are uniformly dispersed, indicating that the multi-metal oxide Ti2Zr2O8 (TZO) contained in the Ti2Zr2O8 multi-nanotubes (TZONT) is a single crystal (orthorhombic) phase.

[0107] In addition, it can be confirmed that FCC (large) cations and anions are located at all eight tetrahedral positions, indicating that the crystal structure of the polymetallic oxide Ti2Zr2O8 (TZO) is a fluorite crystal structure with the molecular formula A2B2O8. In addition, since the bonding distances between cations and oxide ions and the positions of cations are analyzed and the density is analyzed based on the packing of atoms, it can be confirmed that the crystal structure of the polymetallic oxide Ti2Zr2O8 (TZO) is also similar to a pyrochlore crystal structure, indicating that the crystal structure of the polymetallic oxide Ti2Zr2O8 (TZO) is a mixed crystal structure of a fluorite crystal structure and a pyrochlore crystal structure.

[0108] Therefore, the prepared polymetallic oxide Ti2Zr2O8 (TZO) has excellent ionic conductivity, excellent thermal stability, and excellent dielectric polarization properties, and at the same time has excellent oxygen storage and release characteristics because a large number of large voids are ensured in its crystal structure when the polymetallic oxide phase is stable. Therefore, a polymer electrolyte membrane prepared to include a nano-network (which includes porous polymetallic oxide nanotubes that satisfy single-phase and crystal structure characteristics) has improved mechanical or chemical properties such as proton conductivity.

[0109] Experimental Example 2: Evaluation of Proton Conductivity of Polymer Electrolyte Membrane for Fuel Cell

[0110] Since a polymer electrolyte membrane with a higher proton conductivity value can provide better PEMFC performance, proton conductivity can be an important property that directly affects the performance of the electrolyte membrane.

[0111] Therefore, the proton conductivities of the polymer electrolyte membranes prepared according to Example 1 and Comparative Examples 1 to 5 were evaluated, and the evaluation results are graphically shown in Figure 5 .

[0112] As Figure 5 shown, it can be confirmed that as the relative humidity increases, the proton conductivity value of each of the polymer electrolyte membranes increases. Specifically, the proton conductivity values of the polymer electrolyte membranes according to Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Comparative Example 4, and Comparative Example 5 were 5.0, 8.1, 7.9, 9.4, 4.4, and 3.2 mS cm -1 , respectively, at a temperature of 80 °C and a humidity of 20% RH, and their proton conductivity values at a humidity of 100% RH were 111.4, 192.9, 189.6, 207.9, 176.0, and 148.9 mS cm -1 .

[0113] That is, it was confirmed that the proton conductivity of the polymer electrolyte membrane according to Example 1 was 1.9 times that of the polymer electrolyte membrane according to Comparative Example 1 at 20% RH and 1.9 times at 100% RH, mainly because the integrated Ti2Zr2O8 multi-nanotubes (TZONT) effectively promoted the diffusion of water itself through the polymer electrolyte membrane.

[0114] That is, a polymer electrolyte membrane prepared to include a nano-network (which includes porous multi-metal oxide nanotubes prepared according to exemplary embodiments of the present invention) has improved chemical properties, such as proton conductivity, both under humid conditions and dry conditions.

[0115] Experimental Example 3: Tensile Test Evaluation of Polymer Electrolyte Membrane for Fuel Cell

[0116] When evaluating the strength of a composite membrane, the mechanical properties of the polymer electrolyte membrane can be an important parameter, and generally, the mechanical strength of the composite membrane can be evaluated using a tensile test. Therefore, the polymer electrolyte membranes prepared according to Example 1 and Comparative Examples 1 to 5 were evaluated using a tensile test, and the evaluation results are graphically shown in Figure 6 .

[0117] As Figure 6 shown, the breaking stress of the polymer electrolyte membrane according to Example 1 was 16.8 N, which was higher than that of Comparative Example 1 (11.7 N), Comparative Example 2 (15.7 N), Comparative Example 3 (15.8 N), Comparative Example 4 (15.4 N), and Comparative Example 5 (14.0 N).

[0118] Furthermore, as a result of evaluating the tensile test after performing a Fenton test (3% H2O2 solution of 2 ppm FeSO4) at a temperature of 80 °C for 120 hours, it was confirmed that the breaking stresses of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Comparative Example 4, and Comparative Example 5 were 9.6, 14.0, 14.2, 15.6, 13.9, and 12.5 N, respectively.

[0119] That is, it was confirmed that the mechanical losses of the polymer electrolyte membranes of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Comparative Example 4, and Comparative Example 5 after the Fenton test were 16.6%, 10.7%, 10.4%, 7.2%, 9.5%, and 10.4%, respectively. Therefore, it was confirmed that a polymer electrolyte membrane prepared to include a nano-network (which includes porous multi-metal oxide nanotubes prepared according to the exemplary embodiments of the present invention) has high tensile strength, indicating that the polymer electrolyte membrane also has excellent mechanical properties.

[0120] In addition, after the Fenton test (120 hours at a temperature of 80 °C), the oxidation stability and fluoride release rate (FER) of each of the polymer electrolyte membranes according to Example 1 and Comparative Examples 1 to 5 were measured, and the measurement results are shown in Table 1 below.

[0121] Table 1

[0122] Film Oxidation stability (%) <![CDATA[FER(ppm h -1 g -1 )]]> Comparative Example 1 91.4 0.118 Comparative Example 2 95.7 0.022 Comparative Example 3 95.4 0.026 Example 1 96.3 0.021 Comparative Example 4 96.4 0.022 Comparative Example 5 94.2 0.025

[0123] As shown in Table 1 above, it can be confirmed that the polymer electrolyte membranes of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Comparative Example 4, and Comparative Example 5 showed oxidation stabilities of 91.4%, 95.7%, 95.4%, 96.3%, 96.4%, and 94.2%, respectively, and in particular, the polymer electrolyte membrane of Example 1 maintained an oxidation stability of 95% even after the Fenton test. Therefore, the Ti2Zr2O8 multi-nanotubes (TZONT) contained in the polymer electrolyte membrane prepared according to Example 1 can inhibit the decomposition of the membrane due to hydroxyl radical attack. At the same time, it can be confirmed that after the oxidation stability test, the polymer electrolyte membranes of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Comparative Example 4, and Comparative Example 5 showed FER values of 0.118, 0.022, 0.026, 0.021, 0.022, and 0.025 ppm h -1 g -1 respectively, and in particular, the polymer electrolyte membrane according to Example 1 has a lower FER value than the polymer electrolyte membrane according to Comparative Example 4.

[0124] That is, it can be confirmed that the interaction between the sulfonic acid group of the Nafion ionomer and the Ti2Zr2O8 multi-nanotubes (TZONT), which is a mechanical and chemical stable bond as a hydrogen bond, serves as a radical scavenging action, indicating that the polymer electrolyte membrane according to Example 1 has a low FER value while having a high tensile modulus and high oxidation stability.

[0125] Experimental Example 4: Cell performance test of fuel cell

[0126] For the fuel cells according to Examples 3 to 4 and Comparative Examples 6 to 11, the fuel cell performance was evaluated under temperature conditions of 80 °C and different humidity conditions (100% RH and 20% RH). In particular, the H2 and O2 flow rates were 300 sccm and a heater was used to prevent water vapor condensation by maintaining the temperature of the gas supply line at 80 °C or higher, and the cooling water temperature was adjusted to 80 °C and 45 °C, respectively, so that the temperatures of the humidifiers reached relative humidities of RH 100% and RH 20%, respectively. The fuel cell performance was evaluated under the above conditions, and the evaluation results are shown in Tables 2 and 3 below. In addition, the relationship between the cell voltage and power density and the current density is graphically shown in Figures 7A to 8B below.

[0127] Table 2

[0128]

[0129] Table 3

[0130]

[0131] Specifically, Figure 7A and 7B show graphs of cell voltage and power density versus current density for fuel cells according to Example 3 (wherein Ti2Zr2O8 multi-nanotubes (TZONT) are only applied to the polymer electrolyte membrane) and Comparative Examples 6 to 10.

[0132] As shown in Table 2 above and Figure 7A and 7B it can be confirmed that the peak power densities of the fuel cells according to Comparative Example 6, Comparative Example 7, Comparative Example 8, Example 3, Comparative Example 9, and Comparative Example 10 are 735, 770, 742, 924, 747, and 707 mW cm -2 respectively. Accordingly, the fuel cell of Example 3 in which Ti2Zr2O8 multi-nanotubes (TZONT) are introduced into the polymer electrolyte membrane shows better performance characteristics than the fuel cells of the comparative examples (including the fuel cell of Comparative Example 10 (Nafion-CeNP-1)).

[0133] Meanwhile, in the Figure 7A and 7B graphs, as the slope increases, the proton conductivity tends to decrease. Specifically, referring to Figure 7B it can be confirmed that, under the adverse humidity condition of 20% RH, compared with the fuel cell according to Comparative Example 6 showing a power loss of about 63%, the fuel cell according to Example 3 can withstand a harsh environment while showing an average relatively low power loss of about 41%. The fuel cell prepared according to the exemplary embodiments of the present invention has a high peak power density even under low humidity conditions and thus has excellent fuel cell performance.

[0134] Furthermore, Figure 8A and 8B are graphs showing cell voltage and power density versus current density for fuel cells according to Example 4 and Comparative Example 11 in which Ti2Zr2O8 multi-nanotubes (TZONT) are applied to the positive electrode.

[0135] As shown in Table 3 above and Figure 8A it can be confirmed that, under the humidity condition of 100% RH, the peak power densities of the fuel cells according to Example 4 and Comparative Example 11 are 1050 and 850 mW cm -2Therefore, even when the positive electrode obtained using Ti2Zr2O8 multi-nanotubes (TZONT) is additionally applied, the peak power density of the fuel cell according to Example 4 including the polymer electrolyte membrane obtained using Ti2Zr2O8 multi-nanotubes (TZONT) is shown to be 1.2 times that of Comparative Example 11 (not including the polymer electrolyte membrane obtained using Ti2Zr2O8 multi-nanotubes (TZONT)). At the same time, it can be confirmed that the peak power density of the fuel cell according to Example 4 is 1.1 times that of the fuel cell of Example 3 to which the positive electrode obtained using Ti2Zr2O8 multi-nanotubes (TZONT) is not applied.

[0136] In addition, as shown in Table 3 above and Figure 8B it can be confirmed that, under the humidity condition of 20% RH, the peak power densities of the fuel cells according to Example 4 and Comparative Example 11 are 673 and 512 mW cm -2 respectively. Even when the positive electrode obtained using Ti2Zr2O8 multi-nanotubes (TZONT) is additionally applied, the fuel cell according to Example 4 including the polymer electrolyte membrane obtained using Ti2Zr2O8 multi-nanotubes (TZONT) shows that the peak power density is 1.3 times that of the fuel cell of Comparative Example 11 not including the polymer electrolyte membrane obtained using Ti2Zr2O8 multi-nanotubes (TZONT). At the same time, it can be confirmed that the peak power density of the fuel cell according to Example 4 is 1.2 times that of the fuel cell of Example 3 to which the positive electrode obtained using Ti2Zr2O8 multi-nanotubes (TZONT) is not applied.

[0137] That is, it can be confirmed that the fuel cell prepared according to the exemplary embodiments of the present invention has improved moisture retention ability through additional proton channels even under low humidity conditions, and thus exhibits a free radical scavenging effect on membrane stability even under poor conditions, indicating that the fuel cell can have improved performance.

[0138] Experimental Example 5: Measuring the fluoride emission rate (FER) value through the open circuit voltage (OCV) holding test of the fuel cell

[0139] For the fuel cells according to Example 3 and Comparative Example 6, the open circuit voltage (OCV) holding test was carried out under the temperature condition of 80 °C and the humidity condition of 20% RH. The liquid discharged from each of the negative electrode and the positive electrode was collected every 24 hours, and its fluoride release rate (FER) value was measured as the concentration of fluoride ions. The measurement results are shown in Figure 9A and 9B and Figure 10 .

[0140] Specifically, Figure 9A and9B It shows the fluoride release rate (FER) values on the negative electrode (anode) side Figure 9A of the polymer electrolyte membrane according to the open circuit voltage (OCV) holding test and the positive electrode (cathode) side Figure 9B of the polymer electrolyte membrane according to the open circuit voltage (OCV) holding test.

[0141] Thus, it can be confirmed that the FER value (F - ion concentration) of the fuel cell according to Comparative Example 6 was relatively constant from 24 hours to 96 hours, but increased rapidly after 120 hours. On the other hand, the FER value of the fuel cell according to Example 3 continued to decrease.

[0142] As a result, it can be confirmed that after 120 hours, the F - ion concentrations on the anode and cathode sides of the polymer electrolyte membrane in the fuel cell according to Example 3 were 1.6×10 -4 and 1.8×10 -4 ppm h -1 cm -2 respectively, while the F - ion concentrations on the anode and cathode sides of the polymer electrolyte membrane in the fuel cell according to Comparative Example 6 were 3.3×10 -2 and 1.7×10 -2 ppm h -1 cm -2 respectively. Therefore, after 120 hours, the FER values on the anode and cathode sides of the polymer electrolyte membrane in the fuel cell according to Example 3 were 208 times and 93 times lower than the FER values of the polymer electrolyte membrane in the fuel cell according to Comparative Example 6.

[0143] Hydroxyl radicals can be formed from hydroperoxides formed by the chemical reaction of O2 and H2 or by the electrochemical oxygen reduction reaction caused by the two-electron process during battery operation. From the above results, it can be specifically confirmed that the polymer electrolyte membrane in the fuel cell according to Comparative Example 6 was attacked by hydroxyl radicals, resulting in the formation of pinholes or cracks at the cathode site, thereby increasing the discharged fluoride ion concentration and thus allowing O2 gas to permeate to the anode side to form H2O2 in a chemical form, indicating that the deterioration of the polymer electrolyte membrane can proceed to the anode side.

[0144] In summary, it can be confirmed that the polymer electrolyte membrane in the fuel cell according to Example 3 has a low FER value by preventing the attack of hydroxyl radicals, indicating that the polymer electrolyte membrane has excellent durability.

[0145] Meanwhile, Figure 10 It is a graph showing the time-dependent results of the open circuit voltage (OCV) holding test of the fuel cell according to Example 3 under the temperature condition of 80°C and the humidity condition of 20% RH.

[0146] Thus, it can be confirmed that the OCV value of the polymer electrolyte membrane in the fuel cell according to Example 3 remains at 0.8 V or higher up to 270 hours, and its OCV reduction rate is about 0.37 mV / h -1 . Therefore, it can be confirmed that when Ti2Zr2O8 multi-nanotubes (TZONT) are introduced into the polymer electrolyte membrane, even in a harsh environment under low humidity conditions, the polymer electrolyte membrane can improve durability, and at the same time, the fuel cell including the same can have improved performance.

[0147] That is, according to various exemplary embodiments of the present invention, porous multivalent metal oxide nanotubes having a single-phase multivalence can be obtained in high yield without using harmful chemicals. In particular, the porous multivalent metal oxide having a single-phase multivalence is characterized in that it not only has excellent ion conductivity, excellent thermal stability, and excellent dielectric polarization performance, but also has excellent oxygen storage and release characteristics such as a large number of large voids, which are ensured by the crystal structure of the porous multivalent metal oxide, while the phase of the multivalent metal oxide is stable. Therefore, a polymer electrolyte membrane prepared to include a nanonet (which includes nanotubes containing the porous multivalent metal oxide satisfying the above characteristics) can maintain and improve mechanical strength, and thus can maintain durability even during battery operation and can have improved proton conductivity even at low humidity. Therefore, the fuel cell including the polymer electrolyte membrane can have improved performance.

[0148] As described above, according to various exemplary embodiments of the present invention, porous multivalent metal oxide nanotubes having a single-phase multivalence can be obtained in high yield without using harmful chemicals. In addition, a polymer electrolyte membrane including the porous multivalent metal oxide nanotubes prepared according to various exemplary embodiments of the present invention can maintain and improve mechanical strength, and thus can maintain durability even during battery operation and can have improved proton conductivity even at low humidity. Therefore, the fuel cell including the polymer electrolyte membrane can have improved performance.

[0149] The effects of the present invention are not limited to the above effects. It should be understood that the effects of the present invention include all effects that can be deduced from the above description.

Claims

1. A method for preparing porous multi-metal oxide nanotubes, which comprises the following steps: Preparing a mixture comprising two metal-acetylacetonate precursors, polyacrylonitrile and a solvent component; Preparing a nanocomposite from the mixture, Calcining the nanocomposite, wherein the calcined nanocomposite contains a multi-metal oxide having a mixed crystal structure of a fluorite crystal structure and a pyrochlore crystal structure, wherein the metals of the two metal-acetylacetonate precursors include a first non-radioactive metal stable isotope and a second non-radioactive metal stable isotope; wherein the first non-radioactive metal stable isotope is titanium Ti, and the second non-radioactive metal stable isotope is zirconium Zr.

2. The method according to claim 1, wherein the step of preparing the nanocomposite comprises electrospinning the mixture.

3. The method according to claim 1, wherein the two metal-acetylacetonate precursors comprise a titanium acetylacetonate precursor and a zirconium acetylacetonate precursor, wherein the titanium and zirconium in the precursors are both in the +4 valence state, and wherein the molar ratio of titanium acetylacetonate:zirconium acetylacetonate is 1:1 to 1.

4.

4. The method according to claim 1, wherein based on 100 parts by weight of the polyacrylonitrile, the content of the two metal-acetylacetonate precursors is 10 to 50 parts by weight.

5. The method according to claim 2, wherein the electrospinning is carried out by an electrospinning device, in which the distance between the spinneret and the collector is 8 to 12 cm, the high-voltage power in the electrospinning is 15 to 22 kV, and the volume flow rate during the electrospinning is 0.8 to 1 mL / h -1 , the rotational speed of the spinning solution is 300 to 1000 rpm, and the electrospinning is carried out in an ambient air atmosphere.

6. The method according to claim 1, wherein the calcination step is carried out by calcining the nanocomposite at a temperature higher than 400 °C and not higher than 600 °C for 1 to 5 hours and / or the heating rate during the calcination in the calcination step is 4 to 6 °C / minute.

7. The method according to claim 1, wherein the calcination step comprises stabilizing the nanocomposite at a temperature of 230 °C to 250 °C for 0.5 to 1.5 hours before calcining the nanocomposite.

8. A porous multi-metal oxide nanotube, which comprises a multi-metal oxide represented by the following formula and having a single-phase multivalent state: [Formula] A2B2O8 Among them, A is a first non-radioactive metal stable isotope ion, and B is a second non-radioactive metal stable isotope ion; wherein: the first non-radioactive metal stable isotope ion is titanium Ti, and the second non-radioactive metal stable isotope ion is zirconium Zr, wherein the multi-metal oxide has a mixed crystal structure of a fluorite crystal structure and a pyrochlore crystal structure.

9. The porous multi-metal oxide nanotube according to claim 8, wherein the multi-metal oxide has a single-phase orthorhombic crystal form.

10. The porous multi-metal oxide nanotube according to claim 8, wherein the ratio of the A-ion radius to the B-ion radius of the multi-metal oxide is 0.7 to 1.

1.

11. The porous multi-metal oxide nanotube according to claim 8, having an average pore diameter of 10 to 20 nm.

12. A polymer electrolyte membrane, which comprises an ion conductor in pores of a nanonet comprising the porous multi-metal oxide nanotube according to claim 8.

13. The polymer electrolyte membrane according to claim 12, wherein the content of the porous multi-metal oxide nanotubes is 0.5 to 1.5 wt% based on the total weight of 100 wt% of the polymer electrolyte membrane.

14. An electrode, comprising: The porous multi-metal oxide nanotubes according to claim 8; and a binder.

15. The electrode according to claim 14, wherein the content of the porous multi-metal oxide nanotubes is 0.5 to 1.5 wt% based on the total amount of 100 wt% of the porous multi-metal oxide nanotubes and the binder.

16. A fuel cell comprising the polymer electrolyte membrane according to claim 12.

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