KR20150028529A - Nb-TiO2 CATALYST SUPPORTS AND METHOD FOR SYNTHESIS OF THE SAME USING ELECTROSPINNING - Google Patents

Abstract

In the present invention, provided is a catalyst support having a high electrical conductivity at various burning temperatures in PEMFC by using TiO_2 nanofiber doped with Nb by using electrospinning. The present invention relates to a TiO_2 catalyst support doped with Nb and a manufacturing method thereof wherein the catalyst support is used in electrodes for fuel cells and accordingly provides an outstanding activity and resistance to corrosion. In an embodiment of the present invention, provided is a Nb-TiO_2 catalyst support for fuel cells wherein the Nb-TiO_2 catalyst support is nanofiber and is manufactured by using the electrospinning and Nb content of the nanofiber is not more than is 50 at%.

Description

TECHNICAL FIELD The present invention relates to an Nb-TiO 2 catalyst support and a method of manufacturing the same using Nb-TiO 2 catalyst support and electrospinning.

The present invention relates to a Nb-doped TiO ₂ catalyst carrier and a method for producing the same, wherein the catalyst carrier is applied to an electrode for a fuel cell to provide excellent activity and corrosion resistance.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an electrochemical power generation device that produces electricity by reacting hydrogen and oxygen. Carbon black has been used as a typical catalyst carrier material in PEMFC due to its high surface area and high electrical conductivity. However, in the start / stop process of the fuel cell, the carbon carrier causes serious corrosion. Thus, the use of non-carbon supports such as metal oxides is considered desirable. Of these, TiO ₂ has been studied extensively as a catalyst carrier for fuel cells due to its low cost, stability in Nafion electrolyte environment, and ease of size and structure control.

In addition, nanostructured materials such as nanofibers are attracting attention as catalyst carriers in PEMFCs. In recent years, electrospinning has been used in the manufacture of carrier materials of nanofiber structures. However, TiO ₂ has a problem of low electrical conductivity for use in PEMFCs, and research has been conducted on TiO ₂ synthesis technology having excellent electrical conductivity.

When the fuel cell is operated for a long period of time, there is a problem that the performance is deteriorated due to the corrosion of the carbon carrier. In order to solve this problem, development of a corrosion resistant carrier is required, and a carrier which has a simpler manufacturing method, superior catalytic activity and improved durability is developed in comparison with existing methods.

Accordingly, the present invention can provide a catalyst carrier exhibiting high electrical conductivity at various firing temperatures in a PEMFC by preparing Nb-doped TiO2 nanofibers by electrospinning.

In order to achieve the above object, the present invention provides a catalyst carrier including Nb-doped TiO ₂ nanofibers used in a fuel cell and a method of manufacturing the same.

In one embodiment of the invention, there is provided a fuel cell, Nb-TiO ₂ catalyst carrier. The Nb-TiO ₂ carrier is a nanofiber, and the content of Nb in the nanofiber is 50 at% or less. The catalyst carrier may be prepared by electrospinning.

In another embodiment of the present invention, there is provided an active catalyst supported on a Nb-TiO ₂ carrier for a fuel cell. In the Nb-TiO ₂ carrier, it characterized in that the nano-fiber, and wherein the active catalyst is Pt, Pt, Au, Ag, Fe, Co, Ni, Ru, Os, Rh, Pd, Ir, W, Sn, Pd, Bi, and alloys of these metals.

In another embodiment of the present invention, there is provided a method of making an Nb-TiO ₂ support comprising the steps of:

(a) preparing a Ni-TiO ₂ precursor spinning solution comprising a Nb precursor, a Ti precursor and a polymer;

(b) performing electrospinning by applying a high voltage of 10 to 30 kV to the precursor solution; And

(c) heat-treating the electrospun Ni-TiO ₂ nanofibers at 600-900 ° C for 30 minutes to 2 hours in an air atmosphere.

The Ti precursor may be selected from the group consisting of titanium tetraisopropoxide, titanium butoxide, titanium tar-butoxide, titanium dihydroxide and titanium tetrachloride.

The precursor of Nb may be selected from the group consisting of niobium ethoxide, niobium oxide, and niobium oxynitride.

 The polymer may be selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone (PVP), polyvinylbutyral (PVB), polyvinyl acetate (PVA), polyacrylonitrile (PAN) , Polycarbonate (PC), and mixtures thereof.

The solvent of the spinning solution may be water, methanol, ethanol, ethyl alcohol, acetone, N, N'-dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP) ₂ Cl ₂ ), chloroform (CH ₃ Cl), tetrahydrofuran (THF), or mixtures thereof.

The content of Nb in the Nb-TiO ₂ nanofiber may be 0 to 50 at%.

Of the invention In another embodiment, a method of manufacturing the active catalyst supported on the Nb-TiO ₂ carrier comprising the following steps is provided:

(a) preparing a Ni-TiO ₂ precursor spinning solution comprising a Nb precursor, a Ti precursor and a polymer;

(b) performing electrospinning by applying a high voltage of 10 to 30 kV to the precursor solution;

(c) heat-treating the electrospun Ni-TiO ₂ nanofibers at 600-900 ° C for 30 minutes to 2 hours under air atmosphere;

(d) atomizing the Nb-TiO ₂ nanofibers;

(e) supporting the active metal nanoparticles on the atomized Nb-TiO ₂ by impregnation; And

(f) adding a reducing agent to the mixture containing the active metal nanoparticles.

The Ti precursor may be selected from the group consisting of titanium tetraisopropoxide, titanium butoxide, titanium tar-butoxide, titanium dihydroxide and titanium tetrachloride.

The precursor of Nb may be selected from the group consisting of niobium ethoxide, niobium oxide, and niobium oxynitride.

 The polymer may be selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone (PVP), polyvinylbutyral (PVB), polyvinyl acetate (PVA), polyacrylonitrile (PAN) , Polycarbonate (PC), and mixtures thereof.

The solvent of the spinning solution may be water, methanol, ethanol, ethyl alcohol, acetone, N, N'-dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP) ₂ Cl ₂ ), chloroform (CH ₃ Cl), tetrahydrofuran (THF), or mixtures thereof.

The content of Nb in the Nb-TiO ₂ nanofiber may be 0 to 50 at%.

The active metal nanoparticles include any one selected from Pt, Pt, Au, Ag, Fe, Co, Ni, Ru, Os, Rh, Pd, Ir, W, Sn, Pd, Bi, can do.

The reducing agent may be NaBH ₄ , LiAlH ₄ , oxalic acid (C ₂ H ₂ O ₄ ), formic acid (HCOOH).

As another embodiment of the present invention, there is provided an electrode for a fuel cell comprising an active catalyst supported on an Nb-TiO ₂ carrier. The fuel cell electrode includes: an electrode substrate; And a catalyst layer disposed on the electrode substrate, the catalyst layer includes an active metal nano-catalyst supported on the Nb-TiO ₂ carrier.

The content of Nb in the Nb-TiO ₂ nanofiber may be 0 to 50 at%.

The active metal nanoparticles include any one selected from Pt, Pt, Au, Ag, Fe, Co, Ni, Ru, Os, Rh, Pd, Ir, W, Sn, Pd, Bi, can do.

As described above, according to the present invention, Nb-doped TiO ₂ nanofibers can be produced by a simple method by electrospinning. Nb-TiO ₂ nanofibers are atomized and mixed with active metal nanoparticles, A mixed catalyst can be produced. That is, the Nb-TiO ₂ nanofibers of the mixed catalyst have a high electrical conductivity, which can increase the catalytic activity and improve the stability of the catalyst. Therefore, when the electrode catalyst layer of the fuel cell is formed using the mixed catalyst, the performance of the fuel cell can be improved and the corrosion resistance can be remarkably increased.

1 is a schematic diagram of an electrospinning method of the present invention.
2 is a graph of thermal gravimetric analysis (TGA) of TiO ₂ nanofibers.
FIG. 3 is a SEM photograph of TiO ₂ nanofibers produced by electrospinning at various temperatures: (a) 600 ° C., (b) 700 ° C., (c) 800 ° C., and (d) 900 ° C. Followed by baking treatment.
Figure 4 is a SEM photograph of a Nb-TiO ₂ nanofiber having a niobium ethoxide in a variety of content: the content of niobium ethoxide (a) is 0%, (b) is 10%, (c) 25%, ( d) is 50%.
5 is a TEM photograph of (a) TiO ₂ and (b) Nb-TiO ₂ nanofibers.
6 (a) is a graph of XRD pattern of TiO ₂ nanofibers by electrospinning calcined at various temperatures, and FIG. 6 (b) is a graph of rutile ratio of TiO ₂ nanofibers according to firing temperature.
FIG. 7 (a) is an XRD pattern graph of Nb-TiO ₂ nanofibers calcined at 700 ° C. in various contents of niobium ethoxide. FIG. 7 (b) is a graph showing the XRD pattern of Nb-TiO ₂ nanofiber according to the content of niobium ethoxide This is a graph of rutile ratio.
8 is an XPS spectrum of Nb-TiO ₂ nanofibers according to the content of niobium ethoxide fired at 700 ° C.
Figure 9 (a) is a graph showing the effect of calcination temperature on the electrical conductivity of TiO ₂ nano-fiber, Fig. 8 (b), the firing temperature, and niobium ethoxide content of the impact on the electrical conductivity of the Nb-TiO ₂ nanofiber .
10 is a TEM photograph of an Nb-TiO ₂ catalyst carrier in which Pt nanoparticles are dispersed on the surface.
Figure 11 (a) is a 0.1 M HClO ₄ solution injection rate 20 mV / s the cyclic voltammetry curves (CVs) of the catalyst to the record in the Ar- saturated at room temperature. 11 (b) is the spinning disk current density for the ORR of the Pt / Nb-TiO ₂ catalyst of the present invention and the commercially available Pt / C catalyst at 1600 rpm.
12 is the round-trip voltage curves (CVs) measured while performing the accelerated endurance test (ADT) on the commercial Pt / C (FIG. 12A) and the Pt / Nb-TiO2 (FIG. 12B) of the present invention.
13 is the spinning disk current density for the ORR measured while performing the accelerated endurance test (ADT) on commercial Pt / C (FIG. 13A) and Pt / Nb-TiO2 (FIG. 13B) of the present invention.
14 shows the electrochemical reaction surface area (Fig. 14A) and ORR activity (Fig. 14B) of the Pt catalyst measured according to the number of cycles while performing the acceleration endurance test (ADT).
FIG. 15 is a TEM photograph before and after the acceleration endurance test (ADT) is performed on commercial Pt / C (FIG. 12A) and Pt / Nb-TiO2 (FIG. 12B) of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention provides Nb-TiO ₂ having high electrical conductivity and high electrochemical stability as a carrier material for PEMFC. Electrospun TiO ₂ nanofibers have a low diameter standard distribution and a relatively uniform diameter. Nb-doped TiO ₂ nanofibers containing niobium ethoxide have a reduced fiber diameter and a smooth surface.

The electrical conductivity is improved by the phase transition from chuseok to rutile, and TiO ₂ The electrical conductivity of nanofibres increases with increasing firing temperature. However, when the firing temperature is increased to about 700 ° C or more, the increase in the electric conductivity is insignificant, so that the preferable firing temperature is about 700 ° C. The electrical conductivity significantly increased with the introduction of Nb, and preferably contained 25 wt% Nb. The addition of further Nb content did not increase the conductivity further.

Preferably, Nb-TiO ₂ The catalyst carrier can be produced at 25 wt% Nb under an air atmosphere at a calcination temperature of about 700 ° C for 1 hour.

Nb-TiO ₂  Synthesis of Catalyst Support

matter

Titanium tetraisopropoxide (TIP, 97%), niobium ethoxide (NE, 99. 95%) , acetic acid (AC, ≥99.7%), polyvinylpyrrolidone (PVP, _w M = 1,300,000) and ethyl alcohol (ETOH, anhydrous) were purchased from Sigma-Aldehyde Chemicals. All reagents were used as purchased without any additional purification.

1. TiO ₂ Preparation of precursor solution

4 ml of AC, 2 ml of TIP and 2 g of PVP were added to 14 ml of ETOH and stirred until completely dissolved. The solution was degassed by ultrasonication for 5 minutes and mixed together. The stirring solution was transferred to the injector and the injector was fixed to the electric room syringe pump.

2. Nb-TiO ₂  Preparation of precursor solution

4 ml of AC, 2 ml of TIP and 2 g of PVP were added to 14 ml of ETOH and stirred until completely dissolved. 0, 10, 25, 50 at.% Of niobium ethoxide was added. The solution was degassed by ultrasonication for 5 minutes and mixed together. The stirring solution was transferred to the injector and the injector was fixed to the electric room syringe pump.

3. Electrospinning

The TiO ₂ precursor solution was injected at a constant rate of 3 ml / h through a stainless steel needle with a flat outlet. Needles with a diameter of 27 G (200 탆) are made to be constant and disturbed. The distance between the tip of the needle and the collector plate was 10 cm, and the power was 20 kV. Due to the external electrostatic field and the electrostatic repulsion between the surface charge, so-called "tail cone" was formed at the tip of the needle instead of the droplet. During electrospinning, liquid jets were formed with surface tension balancing effects by electrostatic interactions. The needle slowly moved along two orthogonal paths to randomly deposit TiO ₂ fibers in aluminum foil located on the collector plate. Over time, fibers of white mat were obtained. The nanofibers were dried at room temperature for 15 hours.

4. Firing ( calcination )

The conversion of IP to crystalline TiO ₂ and the complete removal of the PVP nanofibers were done at 600-900 ° C for 1 hour.

1. Thermal gravimetric analysis (TGA)

In order to examine the proper sintering temperature of the TiO ₂ nanofiber, the thermal gravimetric analysis was performed for the synthesized TiO ₂ nanofiber (TGA). The weight change was measured by raising the temperature from 20 ° C to 900 ° C in an air atmosphere at a rate of 10 ° C / min.

The TGA curve of the TiO ₂ nanofiber is shown in FIG. According to the thermal gravimetric analysis, three major slope changes can be observed in the weight reduction curve. The weight loss (7.43%) due to the evaporation of acetic acid, ethanol and water was observed up to 270 ℃. From 270 ℃ to 320 ℃, TGA showed significant weight loss (56.40%) by evaporation of the polymer used for electrospinning. The decomposition and removal of the polymer chain occurred at 320 ° C or higher, and oxidation and conversion of the precursor to TiO ₂ nanofiber were observed at 500 ° C.

2. Electron Scanning Microscope (SEM)

3 is a SEM photograph of TiO ₂ nanofibers by electrospinning calcined at various temperatures. The surface of the TiO ₂ nanofiber annealed at 600 ° C was soft (Fig. 3 (a)). The surface of the TiO ₂ nanofiber annealed at 700 ° C or higher was rough (Fig. 3 (b) - (d)). The change of the surface structure according to the firing temperature is due to the difference in crystal formation and denaturation (eg, chuseom and rutile) of TiO ₂ nanofiber.

In addition, the size distribution of the TiO ₂ nanofibers was measured at various firing temperatures, and the average diameters of the TiO ₂ nanofibers calcined at 600, 700, 800, and 900 ° C. were 178.5 nm, 176.5 nm, 177.5 nm and 181.5 nm, respectively . The average fiber diameter distribution was low.

4 is an SEM photograph of Nb-TiO ₂ nanofibers having various contents of niobium ethoxide. The surface of the pure TiO ₂ nanofiber is rough (Fig. 4 (a)). The Nb-doped TiO ₂ nanofiber contains niobium ethoxide, has a reduced fiber diameter and a smooth surface (FIGS. 4 (b) - (d)). This is due to the decrease in the viscosity of the electrospinning solution as the content of niobium ethoxide increases.

In addition, the size distribution of Nb-TiO ₂ nanofibers having various contents of niobium ethoxide was measured, and the average diameter of TiO ₂ nanofibers having 0%, 10%, 25% and 50% niobium ethoxide, respectively, was 171.5 nm, 165.5 nm, 158.5 nm and 153.5 nm. The average fiber diameter distribution is low.

3. Electron transmission microscope (TEM)

5 is a TEM photograph of TiO ₂ nanofiber (a) and Nb-TiO ₂ nanofiber (b). The TiO ₂ nanofibers have a nanofiber structure with a diameter of 50 nm, and the Nb-doped TiO ₂ nanofibers have a nanofiber structure with a diameter of 10-30 nm. This means that the degree of doping at the same manufacturing conditions reduces the diameter of the nanofibers.

4. X-ray diffraction ( XRD )

The XRD pattern in Figure 6 (a) shows TiO ₂ nanofibers at various firing temperatures. The electrospun TiO ₂ nanofibers fired at 600 ° C had a crystal structure in which anatase and rutile were mixed and formed a peak at 2θ = 25.5 ° corresponding to the crystal plane of Example 101. The rutile peaks at 2θ = 27.7 °, 36.1 ° and 54.4 °, which correspond to the (110), (101) and (211) crystal faces of rutile TiO ₂ , respectively. The ratio of rutile phase increased in the TiO ₂ nanofibers calcined above 600 ℃ and phase transition to pure rutile phase at 900 ℃ was completed.

6 (b) is a graph showing the rutile portion of the TiO ₂ nanofibers at different firing temperatures. Example In order to measure the amount of degeneration of rutile into rutile, an XRD peak intensity ratio was used in Figure 5 (a).

The ratio of rutin to rutile extracted from the XRD spectrum is reported in Depero et al. (LE Depero, L. Sangaletti, B. Allieri, E. Bontempi, R. Salari, M. Zocchi and M. Notaro, J. Mater . Res . , 13 , 1644, (1998)).

Where R (T) is the percentage of rutile content at each temperature, and I _A is the intensity of the main example night reflection (101) (2? = 25.30 °). I _R is the intensity of the main rutile reflection (110) (2θ = 27.44 °.

The electrospun TiO ₂ nanofibers fired at 600 ° C have 30% of the rutile structure, 78% at 700 ° C, 93% at 800 ° C and 100% rutile structure at 900 ° C. At 600 ℃ -700 ℃, TiO ₂ nanofibers underwent a phase change from mullite to rutile.

7 (a) is an XRD pattern graph of Nb-TiO ₂ nanofibers calcined at 700 ° C in various contents of niobium ethoxide. The rutile peak 110 appeared at 2? = 27 ° in Fig. 6 (a). The peak intensity was decreased with respect to the synthetic nanofibers containing niobium ethoxide (Fig. 6 (a)). That is, the crystallinity decreased when niobium was added.

7 (b) is a graph of rutile ratio of Nb-TiO ₂ nanofibers according to the content of niobium ethoxide. Example In order to calculate the ratio of Chuseok to rutile, the XRD peak intensity ratio of FIG. 6 (a) was used. The rutile portions of Nb-TiO ₂ at 0%, 10%, 25% and 50% were 78%, 30%, 58% and 45%, respectively. When the niobium ion is replaced with TiO ₂ , the charge of the Nb ^{5 +} ion must compensate for the reduction of the oxygen vacancy, thereby interfering with the phase transition to the rutile.

5. X-ray photoelectron spectrum ( XPS )

8 is an XPS spectrum of Nb-TiO ₂ nanofibers according to the content of niobium ethoxide calcined at 700 ° C. Peak position of Ti 2p _3/2 corresponds to the peak position of Ti ^{4 +} oxidation states. Peak position of Ti 2p _3/2 in T459.2 eV is the same as in the Nb-TiO ₂ nanofiber. Peak position of the 207.2 eV Nb 3d _5/2 corresponds to the peak position of the Nb ^{4 +} oxidation states. By compensation per Ti Nb 4 cation vacancies introduced in the Nb ^{5 +} charge for the substitution of Ti ^{4 +} I (instead of Ti ^{4 +} to be reduced to Ti ^{+ 3)} is obtained by the following equation.

6. Electrical conductivity

Figure 9 (a) shows the effect of firing temperature on the electrical conductivity of the TiO ₂ nanofibers. The electrical conductivity of TiO ₂ nanofibers increases as the firing temperature increases. The lowest electrical conductivity of TiO ₂ nanofibers at 600 ° C was 6.1 × 10 ^-5 S / cm and the maximum electrical conductivity was 4.9 × 10 ^-4 S / cm at 900 ° C. However, the electric conductivity increase range from 700 ˚ C to 900 ˚C was 4.3 × 10 ^-4 S / cm to 4.9 × 10 ^-4 S / cm. The increase in the electrical conductivity with increasing temperature is due to the increase in the crystallization of the rutile. TiO ₂ has an example of a mullite structure below 600 ° C, but phase transition occurs from mullite to rutile at 600-700 ° C. The electrical conductivity increases as the phase transition progresses above 600 ° C and the rutile ratio increases. Example The crystallization of chuseom and rutile was observed at 600 ° C or higher and the XRD pattern air of the annealed TiO ₂ nanofiber can be clearly confirmed (FIG. 6 (a)).

Example Chuseok has a bandgap of 3.2 eV, and rutile has a low bandgap at 3.0 eV. The low bandgap allows electrons to move easily from the balanced bandgap to the conduction band. The bandgap is a key factor in measuring electrical conductivity.

On the other hand, the electrical conductivity of Nb-TiO ₂ nanofibers was measured according to the content of niobium ethoxide. By introducing Nb, the electrical conductivity was significantly increased and the highest conductivity was 25% Nb in Nb-doped TiO ₂ nanofibers . An additional increase in the Nb content did not lead to an increase in continuous conductivity. Nb ^{5 +} ion implantation into the TiO ₂ lattice induces electron donation to the conduction band, thereby increasing the charge carrier concentration. The balanced state of the metal atoms in the Nb-doped titania lattice exhibits successful doping in electrical conductivity. This is directly related to the specific defects formed in the doping process.

Figure 9 (b) shows the effect of firing temperature and niobium ethoxide content on the electrical conductivity of Nb-TiO ₂ nanofibers. The electrical conductivity increased with the firing temperature, the electrical conductivity increased significantly with the addition of Nb, and the highest conductivity was at 25% Nb content. An additional increase in the Nb content did not result in any further improvement.

Pt / Nb-TiO ₂  Preparation of Catalyst

matter

Ethyl alcohol (ETOH, anhydrous), sodium borohydride (NaBH ₄ ) and chloroplatinic acid (H ₂ PtCl ₆ .6H ₂ O) were purchased from Sigma-Aldrich Chemical and all reagents were used as purchased without further purification. Nb _0.25 Ti _0.75 O ₂ was used as the catalyst carrier.

Produce

The Pt (20 wt%) catalyst supported on Nb-TiO ₂ was prepared by the borohydride reduction method.

An appropriate amount of chloroplatinic acid (H ₂ PtCl ₆ .6H ₂ O) was dissolved in the ETOH. The Nb-TiO ₂ carrier was dispersed in ETOH, and a metal salt solution was added and mixed with stirring. The pH of the suspension was then adjusted to 8.5. The metal salt and the Nb-TiO ₂ carrier were reduced using an excess of NaH ₄ solution. The suspension was stirred for 2 hours. The precipitate was washed with deionized water and dried at 40 < 0 > C for 24 hours.

A commercially available Pt / C catalyst loaded with 20 wt% Pt as a reference point was synthesized on a commercially available vulk carrier by the modified ethyl glycol method.

1. Electron transmission microscope (TEM)

10 is a TEM photograph of an Nb-TiO ₂ catalyst carrier in which Pt nanoparticles are dispersed on the surface. It can be seen that the Pt nanoparticles are granular and relatively uniformly dispersed in the Nb-TiO ₂ catalyst carrier.

On the other hand, Pt / Nb-TiO _2. The size distribution of the Pt nanoparticles was measured on the surface, and the approximate average value of the Pt nanoparticle diameter was 4 nm. The average particle size for Pt / C commercially available as a reference point was about 2.5 nm (Fig. 12 (a)).

2. Electrochemical properties

Electrochemical experiments are usually performed on RDE 3 electrode cells. The counter electrode is a platinum wire, and the reference electrode is a saturated calomel electrode (SCE). The electrolyte is a 0.1 M HClO ₄ solution. This solution was made from distilled water and bubbled with high purity argon (Ar) gas to remove oxygen in the solution. The solution temperature was maintained at 25 degrees.

10 mg of Pt / NbTiO ₂ catalyst was dispersed by ultrasonication in 800 μl of IPA and 60 μl of Nafion solution (5 wt% solution, Aldrich) to prepare a catalyst ink. 5 잉크 of the ink was transferred to a glass carbon rotary disc electrode (RDE, 5 mm in diameter) by a micropipette, and was dried. A commercially available Pt / C ink was prepared according to the same method.

3. Cyclic Voltammetric Method (CV)

The cyclic voltammetry (CV) experiment was performed at potentials 0 to 1.1 V _RHE . The electrochemically active surface (EAS) was evaluated based on the H2 desorption peaks observed at 0.05 to 0.35 V _RHE . The hydrogen desorption potential, 0.21 mC / cm ^2, was assumed in the calculation of the active Pt fraction.

Here, [Pt] means platinum loading at the electrode and QHsms is the charge of H ₂ desorption. Figure 11 (a) shows the cyclic voltammetric curves (CVs) of these catalysts recorded at a scanning rate of 20 mV / s in a 0.1 M HClO ₄ solution saturated at room temperature with Ar.

A commercially available 20 wt% Pt / C catalyst showed an EAS value of 45.3 m 2 / g and a 20 wt% Pt / Nb-TiO ₂ showed an EAS value of 42.1 m 2 / g. This means that Nb-TiO ₂ has sufficient conductivity to serve as a catalyst carrier.

4. Oxygen reduction reaction (ORR)

An oxygen reduction reaction (ORR) experiment was performed in an oxygen-saturated 0.1 M HClO ₄ solution at room temperature. The RDE rotational speed is 1600 rpm and the voltage sweep rate is 5 mV / s.

ORR activity was observed from 0.75 to 0.95 V. The activity was calculated in the experimental data by calibrating the mass transfer characteristics for the rotating disk electrode according to the following equation:

Where I is the current density measured during the ORR, i _k is the kinetic current density at which the mass transfer resistance is removed, and i _d is the diffusion-limited current density. The activity is determined by calculating i _k using the above equation.

FIG. 11 (b) shows the spinning disk current density for the ORR of Pt / Nb-TiO ₂ catalysts and commercially available Pt / C catalysts of the present invention at 1600 rpm.

In FIG ORR of all the catalyst from 11 (b) is determined by the potential is 0.7 V _RHE The standing diffusion, 0.7 V _RHE at least 0.9 V _RHE or less is determined by the diffusion and reaction. At 0.9 V, the Pt / Nb-TiO ₂ activity (4901 ㎂ / ㎠) is similar to commercial Pt / C (4870 ㎂ / ㎠).

5. Accelerated Endurance Test (ADT)

CV measurements for the accelerated endurance test (ADT) were performed by 0.6 to 1.1 V _RHE potential cycling in 0.1 M HClO ₄ solution O 2 purged at room temperature with a scan rate of 50 mV / s. In each case, the ADT test consists of 6000 cycles.

For comparison, a 20 wt% Pt / Nb-TiO ₂ catalyst according to the present invention and a commercially available 20 wt% Pt / C catalyst were tested under the same dislocation cycling conditions.

Cyclic voltammetry is used to determine the Pt surface area of Pt / Nb-TiO ₂ and commercial Pt / C electrodes of the present invention by measuring H adsorption before and after dislocation cycling.

In Figure 12, Pt / Nb-TiO ₂ is 75% of the original electrochemical reaction area of the Pt remaining after 6000 cycles, which is about 2 times or more than 40% of a commercially available Pt / C catalyst. (Fig. 14 (a)) These results indicate that Pt on the Nb-TiO ₂ support is electrochemically more stable. Improved stability may be due to (a) high corrosion resistance of the Nb-TiO2 carrier compared to carbon under acidic conditions, and (b) strong Pt-metal oxide carrier interaction.

13, the ORR activity of the Pt / Nb-TiO ₂ catalyst was 3127 μA / cm 2 after 6,000 cycles and decreased by about 40% at the initial activity (4901 ㎂ / ㎠). On the other hand, Pt / C decreased by 90% of the initial activity from 670,000 cycles at 4570 / / ㎠ to 400 ㎂ / ㎠ (Fig. 14B). In addition, Pt / Nb-TiO ₂ showed almost 8 times higher ORR activity than Pt / C catalyst after the dislocation cycling experiment.

15 is a TEM photograph of the Pt / Nb-TiO ₂ catalyst of the present invention and a commercially available Pt / C catalyst before and after the ADT experiment. Figure 12 shows well aligned Pt particles on a carbon carrier. The average size of the platinum particles was calculated to be 2 to 3 nm. The Pt particle size of the Pt / C catalyst increased from 2-3 to 6-10 mm after dislocation cycling. The increase in Pt particle size implies that the main cause for platinum EAS loss in Pt / C catalysts is due to Pt agglomeration due to carbon corrosion. In contrast, the Pt / Nb-TiO ₂ catalyst showed little change in Pt particle size before and after the dislocation cycling experiment. This indicates that the Pt / Nb-TiO ₂ catalyst of the present invention has the same initial performance as that of the commercial Pt / C and has excellent durability.

Claims (21)

The content of Nb is 50 at% or less,
Nb-TiO ₂ catalyst support for fuel cells comprising Nb-doped TiO ₂ nanofibers. (a) preparing a Ni-TiO ₂ precursor spinning solution comprising a Nb precursor, a Ti precursor and a polymer;
(b) performing electrospinning by applying a high voltage of 10 to 30 kV to the precursor solution; And
(c) heat-treating the electrospun Ni-TiO ₂ nanofibers in an air atmosphere at 600-900 ° C for 30 minutes to 2 hours
Gt; TiO2 < / RTI _> catalyst carrier. The method of claim 2, wherein the Ti precursor is titanium tetraisopropoxide, titanium butoxide, titanium emitter-butoxide, titanium dihydroxy fuel cell Nb-TiO ₂ catalyst carrier is selected from the side, and the group consisting of titanium tetrachloride ≪ / RTI > 3. The method of claim 2, wherein Nb precursor process for producing a fuel cell, Nb-TiO ₂ catalyst carrier is selected from the group consisting of niobium ethoxide, niobium oxide and niobium oxy you Tide. The method of claim 2, wherein the polymer is selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone (PVP), polyvinylbutyral (PVB), polyvinyl acetate (PVA), polyacrylonite A method for producing a Nb-TiO ₂ catalyst support for a fuel cell selected from polyacrylonitrile (PAN), polycarbonate (PC), and mixtures thereof. 3. The method of claim 2, wherein the solvent of the spinning solution is selected from the group consisting of water, methanol, ethanol, ethyl alcohol, acetone, N, N'-dimethylformamide (DMF), dimethylsulfoxide (DMSO) ), methylene chloride (CH ₂ Cl _2), chloroform (CH ₃ Cl), tetrahydrofuran (THF) or method of making a fuel cell, Nb-TiO ₂ catalyst carrier is selected from a mixture thereof. The method of claim 2, wherein the content of Nb in the Nb-TiO ₂ nanofiber method for producing a fuel cell 50 at% or less Nb-TiO ₂ catalyst carrier. Wherein the second to seventh fuel cell Nb-TiO ₂ catalyst carrier produced according to any one of items. Comprises a Nb-TiO ₂ carrier and the active catalyst supported here,
The Nb-TiO ₂ carrier is a nanofiber,
The active catalyst is any one or more components selected from among Pt, Pt, Au, Ag, Fe, Co, Ni, Ru, Os, Rh, Pd, Ir, W, Sn, Pd, Bi, Featured
Active catalyst supported on Nb-TiO ₂ carrier for fuel cell. (a) preparing a Ni-TiO ₂ precursor spinning solution comprising a Nb precursor, a Ti precursor and a polymer;
(b) performing electrospinning by applying a high voltage of 10 to 30 kV to the precursor solution;
(c) heat-treating the electrospun Ni-TiO ₂ nanofibers at 600-900 ° C for 30 minutes to 2 hours in an air atmosphere;
(d) atomizing the heat-treated Nb-TiO ₂ nanofibers;
(e) supporting the active metal nanoparticles on the atomized Nb-TiO ₂ by impregnation; And
(f) adding a reducing agent to the mixture containing the active metal nanoparticles
Wherein the active catalyst is supported on a Nb-TiO ₂ support for a fuel cell. 11. The method of claim 10, wherein the Ti precursor is titanium tetraisopropoxide, titanium butoxide, titanium emitter-to-butoxide, titanium di-hydroxide and a fuel cell Nb-TiO ₂ carrier is selected from the group consisting of titanium tetrachloride Lt; RTI ID = 0.0 > supported < / RTI > catalyst. 11. The method of claim 10, wherein Nb precursor process for preparing the active supported catalyst for a fuel cell Nb-TiO ₂ carrier is selected from the group consisting of niobium ethoxide, niobium oxide and niobium oxy you Tide. The method of claim 10, wherein the polymer is selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone (PVP), polyvinylbutyral (PVB), polyvinyl acetate (PVA), polyacrylonite A method for producing an active catalyst supported on a Nb-TiO ₂ carrier for a fuel cell selected from polyacrylonitrile (PAN), polycarbonate (PC), and mixtures thereof. 11. The method of claim 10, wherein the solvent of the spinning solution is selected from the group consisting of water, methanol, ethanol, ethyl alcohol, acetone, N, N'-dimethylformamide (DMF), dimethylsulfoxide (DMSO) Wherein the catalyst is supported on a Nb-TiO ₂ support for fuel cells selected from methylene chloride (CH ₂ Cl ₂ ), chloroform (CH ₃ Cl), tetrahydrofuran (THF) or mixtures thereof. 11. The method of claim 10, the method for preparing the active catalyst supported on the content of Nb in the Nb-TiO ₂ nanofiber is 50 at% or less for a fuel cell Nb-TiO ₂ carrier. The active metal nanoparticles according to claim 10, wherein the active metal nanoparticles are selected from among Pt, Pt, Au, Ag, Fe, Co, Ni, Ru, Os, Rh, Pd, Ir, W, Sn, Pd, Bi, Wherein the active catalyst is supported on a Nb-TiO ₂ support for a fuel cell. The method of claim 10 wherein the reducing agent is NaBH _4, LiAlH _4, oxalic acid _{(C 2 H 2 O 4)} , or formic acid (HCOOH) in a fuel cell process for preparing the active catalyst supported on the Nb-TiO ₂ carrier. Of claim 10 to 17 wherein the activity of the catalyst supported on the fuel cell, Nb-TiO ₂ carrier prepared according to any of the preceding. An electrode substrate; And a catalyst layer disposed on the electrode substrate, wherein the catalyst layer comprises an active metal nanocatalyst supported on a Nb-TiO ₂ support. 20. The method of claim 19, wherein the active metal nanocatalyst is selected from Pt, Pt, Au, Ag, Fe, Co, Ni, Ru, Os, Rh, Pd, Ir, W, Sn, Pd, Bi, Wherein the first electrode is made of a metal. The electrode for a fuel cell according to claim 19, wherein the content of Nb in the Nb-TiO ₂ carrier is 50 at% or less.

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