KR101975970B1 - Hollow composite, method of preparing the same, and electrocatalyst including the same - Google Patents

Abstract

A hollow composite, a method for producing the hollow composite, an electrocatalyst including the hollow composite, an electrode, a battery including the electrode, an electronic ink including the hollow composite, and an electronic paper including the electronic ink and a display device .

Description

TECHNICAL FIELD [0001] The present invention relates to a hollow composite, a method for producing the hollow composite, and an electrocatalyst including the same. BACKGROUND OF THE INVENTION [0002]

The present invention relates to a hollow composite, a method for producing the hollow composite, an electrocatalyst comprising the hollow composite, an electrocatalyst comprising the hollow composite, an electrode, a battery comprising the electrode, an electronic ink comprising the hollow composite, An electronic paper including the electronic ink, and a display device.

Increased energy demand and reduced predicted fossil fuel supply have led to the need for clean, sustainable energy conversion and efficient development of storage systems at low cost. Particularly, low-emission fuel cells and metal-air batteries with high energy density and reusability have recently attracted attention as a promising energy source. Slow oxygen reduction (ORR) has been expected to limit the performance of the technique. Carbon supported Pt (Pt / C) has been selected as a catalyst for oxygen reduction reaction (ORR) in both acidic and alkaline conditions, despite its high cost and low durability. On the other hand, expensive transition metal oxides including chalcogenides, chalcogenides, and composites of these materials tend to exhibit low electrical conductivity and durability in strong acid and strong base conditions. The study of low cost and efficient ORR catalysts made from abundant components on the earth is of paramount importance as much of an inquiry study focused on promising alternatives with improved applicability. In this context, TiO ₂ has been a subject of interest due to its abundance, low cost, non-toxicity, and high stability over a wide pH range. Recent reports have shown that Pt / TiO ₂ exhibits ORR activity comparable to commercial Pt / carbon black (Pt / carbon black) and excellent stability. However, the application of TiO ₂ as a single ORR electrocatalyst is reported only at low activity values and remains rare in the literature. The relatively low intrinsic conductivity and low activity of TiO ₂ appear to interfere with the efficient use of such materials in fuel cell and electrocatalyst applications requiring fast electron transport.

In order to experimentally improve the electrochemical properties of TiO ₂ , many attempts have been made in the literature (for example, element doping and coupling with carbon materials). TiO ₂ crystals of self-Ti ^{+ 3} followed by the formation of the oxygen defects (oxygen vacancy) into the grid-reported in the literature has been focused on doping a lot of attention. TI ^{3 +} self-Doping known to significantly narrow bandgap (bandgap) of TiO _2, increasing the donor (donor) density and electrical conductivity of TiO _2. Crystal plane (facet) and a defect (defect) has been reported recently that the control of the Ti ^{3 +} TiO ₂ doped nanocrystals (nanocrystal) refers to possible competition ORR activity, excellent durability, and excellent methanol resistance. However, the stability of the Ti ^{3 +} -doped TiO ₂ system remains a challenging task due to the easy oxidation of Ti ³⁺ species.

In an attempt to improve the electrical conductivity of TiO ₂ , hybridization with highly conductive carbonaceous materials has been reported. Because of their excellent electrical conductivity, high mechanical strength, structural flexibility, and large surface area, it has been found that carbon-based materials can be efficiently applied in photovoltaic, photocatalytic, and electrocatalysts. In particular, rGO / TiO ₂ hybrid materials have exhibited higher conductivity and improved thermal and chemical stability. However, despite progress achieved in photocatalysts, water splitting, and solar cells [J. Du, X. Lai, N. Yang, J. Zhai, D. Kisailus, F. Su, D. Wang, L. Jiang, ACS Nano 2011 , 5 , 590; G. Xie, K. Zhang, B. Guo, Q. Liu, L. Fang, JR Gong, Adv . Mater. 2013 , 25 , 3820.; JT-W. Wang, JM Ball, EM Barea, A. Abate, JA Alexander-Webber, J. Huang, M. Saliba, I. Mora-Sero, J. Bisquert, HJ Snaith, RJ Nicholas, Nano Lett . 2014 , 14 , 724.], the application of the rGO / TiO ₂ catalyst system in electrocatalyst applications remains largely unexplored.

Also, rGO / TiO ₂ Study of the hybrid system ³ and Ti ⁺ self-assessment at the same time trying to consider of the doped TiO ₂ is a state that is not investigated in the art.

In this regard, U.S. Published Patent Application No. 2013-0330659 discloses a method for producing a catalyst for an electrode for a fuel cell.

The present invention is directed to a hollow composite, wherein the hollow composite comprises a shell comprising a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid is self-doped by a metal element contained in the metal oxide, doped, and the inner surface of the shell of the hollow composite comprises carbon.

The present invention is directed to a method of making the hollow composite, an electrocatalyst comprising the hollow composite, an electrode comprising the hollow composite, a battery comprising the electrode, an electronic ink comprising the hollow composite, Electronic paper and a display device.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

According to a first aspect of the present invention, there is provided a hollow composite comprising a shell comprising a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid is formed by a metal element contained in the metal oxide, Wherein the inner surface of the shell of the hollow composite is self-doped, and the inner surface of the shell of the hollow composite comprises carbon.

According to a second aspect of the present invention, there is provided a method for producing a core-shell composite comprising coating a polymer core with a mixed solution containing a precursor for a metal oxide and a precursor for a carbon structure to form a core- - shell composite to obtain a hollow composite, wherein the shell of the hollow composite comprises a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid comprises a metal contained in the metal oxide Wherein the first calcination comprises heating the core-shell composite at a first temperature to carbonize and remove the polymer core particles to obtain the hollow composite, By weight, based on the total weight of the hollow composite.

A third aspect of the invention provides an electrocatalyst comprising a hollow composite according to the first aspect of the present invention.

A fourth aspect of the invention provides an electrode comprising a hollow composite according to the first aspect of the present application.

A fifth aspect of the invention provides a cell comprising an electrode according to the fourth aspect of the present application.

A sixth aspect of the invention provides an electronic ink comprising a hollow composite according to the first aspect of the present application.

A seventh aspect of the present invention provides an electronic paper or display device comprising electronic ink according to the sixth aspect of the present application.

According to one embodiment of the invention, the hollow composite comprises a shell comprising a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid is self-doped by a metal element contained in the metal oxide, The inner surface of the shell of the hollow composite contains carbon, so that the electrical conductivity of the hollow composite is improved, and the electrocatalytic activity for the oxygen reduction reaction is exhibited similar to the activity of the existing Pt / C.

According to one embodiment of the present invention, the hollow composite is improved in stability in an alkali medium in the oxygen reduction reaction by hybridization of the metal oxide and the carbon structure, self-doping by the metal element, and carbon, The resistance increases.

In one embodiment of the invention, the hollow composite comprises an electrocatalyst, in particular an electrocatalyst for an oxygen reduction reaction, an electrode, in particular an electrode for oxygen reduction reaction, a battery comprising the electrode, an electronic ink, Electronic paper and display devices.

FIG. 1A is a flow chart illustrating a process for producing an rGO / TiO ₂ hollow composite in one embodiment of the present invention. FIG.
1B is a schematic diagram illustrating a process for making an rGO / TiO ₂ hollow composite, in one embodiment of the present invention.
Figure 2 is a schematic diagram of an embodiment of the present invention, wherein in one embodiment of the present invention, PS nanospheres, (b) PS @ GO / TiO ₂ , (c) TiO ₂ , and (d) rGO (10%) / TiO ₂ hollow SEM images of each of the composites.
Figure 3, in one embodiment of the present _{application, (a) PS @ TiO 2} , (b) rGO (5%) / TiO 2, and (c) rGO (20%) / TiO 2 hollow composite each FESEM image And (d) a FESEM image (scale bar is 1 μm) showing a cross-sectional view of the rGO (10%) / TiO ₂ hollow composite.
Figure 4 shows TEM images of (a) TiO ₂ (air), (b) TiO ₂ , (c) rGO (20%) / TiO ₂ hollow, and (d) rGO 20%) / TiO ₂ .
Figure 5 is, in one embodiment of the present application, (a) TiO ₂ TEM image, (b) HRTEM image showing the presence of a carbon layer on the TiO ₂ nanoparticles of hollow composite, and (c) rGO (10%) / TEM image of TiO ₂ hollow composite and (d) HRTEM image, respectively.
Figure 6 is a graph showing the N ₂ adsorption-desorption measurements of different samples, respectively, in one embodiment of the invention.
Figure 7a shows a synchrotron X-ray diffraction pattern of the crystalline phase of the TiO ₂ and rGO / TiO ₂ hollow composite, in one embodiment of the invention.
FIG. 7B is a Raman spectrum of a hybrid structure for investigating the binding characteristics of rGO and TiO ₂ in one embodiment of the present invention. FIG.
Figures 8a to 8f has, in one embodiment of the invention, and to investigate the chemical state and the effective integration of rGO and TiO ₂ - shows the resolution X- ray photoelectron spectroscopy measurements.
Figure 9a shows the standardized XANES spectra of calcined Comparative TiO ₂ reference, TiO ₂ , and rGO (10%) / TiO ₂ hollow nanospheres calcined under air (TiO ₂ air).
Figure 9b, in one embodiment of the invention, compared to calcined under air (TiO ₂ air) for example TiO ₂ reference, TiO _2, and rGO (10%) / TiO ₂ free of the hollow nanospheres - XANES indicating the edge position It is an enlarged image of the spectrum.
Figure 10a shows, in one embodiment of the invention, a Nyquist plot of all evaluated samples.
FIG. 10B shows a Mott-Schottky measurement of the sample in one embodiment of the present invention.
Figure 11a is, in one embodiment of the present application, shows a CV curve of rGO / TiO ₂ and Pt / C.
FIG. 11B shows LSV curves of different samples, in one embodiment of the invention.
FIG. 11C shows LSV curves of rGO (10%) / TiO ₂ samples at different rotational speeds, in one embodiment of the invention.
Figure 11d shows a Tafel plot of rGO / TiO ₂ complexes induced by RDE data, in one embodiment of the invention.
Figure 12 is, in one embodiment of the present application, shows a sample each of the CV curves, and different from the rotational speed _{rGO (5%) / TiO 2} , rGO (20%) / TiO 2, and Pt / C Each of the LSV curve .
(A) rGO (5%) / TiO ₂ , (b) rGO (10%) / TiO ₂ , and (c) TiO ₂ derived from ORR plots at different potentials. ) rGO (20%) / TiO 2 each KL plot, and (d) rGO (5%) / TiO 2, rGO (10%) / TiO 2, rGO (20%) / TiO 2, and e of the Pt / C Represents the number of movements.
Figure 14a shows the time-to-current response of each sample at 0.5 V versus RHE at a rotational speed of 1,600 rpm for 20,000 seconds in one embodiment of the invention.
Figure 14b shows the methanol tolerance of the synthetic sample at 0.5 V versus RHE at a rotational speed of 1,600 rpm, in one embodiment of the invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is " on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as " including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms " about ", " substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) " or " step " used to the extent that it is used throughout the specification does not mean " step for.

Throughout this specification, the term " combination thereof " included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

According to a first aspect of the present invention, there is provided a hollow composite comprising a shell comprising a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid is formed by a metal element contained in the metal oxide, Wherein the inner surface of the shell of the hollow composite is self-doped, and the inner surface of the shell of the hollow composite comprises carbon.

In one embodiment of the present invention, the metal oxide may include a semiconductor oxide, for example, TiO ₂ , SnO ₂ , ZnO, VO ₂ , In ₂ O ₃ , NiO, MoO ₃ , SrTiO ₃ , Fe-doped SrTiO ₃ , Fe ₂ O ₃ , WO ₃ , CuO, BiVO ₄ , And combinations of these. ≪ RTI ID = 0.0 > [0040] < / RTI >

In one embodiment, the carbon structure is selected from the group consisting of reduced graphene oxide (rGO), graphene, graphite, single wall carbon nanotubes, multiwall carbon nanotubes, carbon nanohorns, Synthetic carbon sources including acetylene black, carbon black formed from the combustion of hydrocarbons or polymers (for example, Kecheon black), and carbon black And a carbon structure selected from the group consisting of combinations thereof.

In one embodiment of the present invention, the metal element may be in a reduced state than the metal cation contained in the metal oxide. The reduced metal cation is in a reduced state and is unstable and prone to oxidation. However, the carbon formed on the inner surface of the shell and the reduced metal cation are stabilized by the carbon structure to self-dope the hybrid. For example, if the metal oxide contained in the shell include TiO _2, the Ti ^{4 +} contained in the TiO ₂ is partially reduced to the Ti ^{3 +} the Ti ^{3 +} in the hollow composite stabilization of the hollow composite Became The hybrids can be self-doped by the stabilized Ti ³⁺ .

In one embodiment herein, the size of the hollow composite can be from about 50 nm to about 5,000 nm. The size of the hollow composite may vary depending on the shape of the hollow composite. For example, in the case of a spherical shape, the diameter of the spherical hollow may be used, and in the case of an elliptical shape, the diameter of the long axial or short axis may be used. The size of the hollow complex can be, for example, from about 50 nm to about 5,000 nm, from about 100 nm to about 5,000 nm, from about 300 nm to about 5,000 nm, from about 500 nm to about 5,000 nm, from about 700 nm to about 5,000 nm From about 1,000 nm to about 5,000 nm, from about 1,300 nm to about 5,000 nm, from about 1,500 nm to about 5,000 nm, from about 1,700 nm to about 5,000 nm, from about 2,000 nm to about 5,000 nm, from about 2,500 nm to about 5,000 nm, From about 3,000 nm to about 5,000 nm, from about 3,500 nm to about 5,000 nm, from about 4,000 nm to about 5,000 nm, from about 4,500 nm to about 5,000 nm, from about 50 nm to about 4,500 nm, from about 50 nm to about 4,000 nm, From about 50 nm to about 1500 nm, from about 50 nm to about 3,000 nm, from about 50 nm to about 2,500 nm, from about 50 nm to about 2,000 nm, from about 50 nm to about 1,700 nm, from about 50 nm to about 1,500 nm, From about 50 nm to about 100 nm, from about 50 nm to about 100 nm, from about 50 nm to about 700 nm, from about 50 nm to about 500 nm, from about 50 nm to about 300 nm, from about 50 nm to about 100 nm, From about 500 nm to about 4000 nm, from about 700 nm to about 4000 nm, from about 1,000 nm to about 4,000 nm, from about 1,300 nm to about 4,000 nm, from about 1,500 nm to about 4,000 nm From about 2,000 nm to about 4,000 nm, from about 2,500 nm to about 4,000 nm, from about 3,000 nm to about 4,000 nm, from about 3,500 nm to about 4,000 nm, from about 100 nm to about 3,500 nm, From about 100 nm to about 1500 nm, from about 100 nm to about 1,300 nm, from about 100 nm to about 3,000 nm, from about 100 nm to about 2,500 nm, from about 100 nm to about 2,000 nm, from about 100 nm to about 1,700 nm, From about 100 nm to about 500 nm, from about 100 nm to about 300 nm, from about 200 nm to about 2,000 nm, from about 300 nm to about 2,000 nm, from about 400 nm to about 500 nm, From about 500 nm to about 2,000 nm, from about 600 nm to about 2,000 nm, from about 700 nm to about 2,000 nm, from about 800 nm to about 2,000 nm, from about 900 nm to about 2,000 nm, From about 1,200 nm to about 2,000 nm, from about 1,200 nm to about 2,000 nm, from about 1,300 nm to about 2,000 nm, from about 1,400 nm to about 2,000 nm, from about 1,500 nm to about 2,000 nm, from about 1,600 nm to about 2,000 nm about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 1,700 nm to about 2,000 nm, about 1,800 nm to about 2,000 nm, about 1,900 nm to about 2,000 nm, From about 200 nm to about 1,100 nm, from about 200 nm to about 1,100 nm, from about 200 nm to about 1,500 nm, from about 200 nm to about 1,400 nm, from about 200 nm to about 1,300 nm, from about 200 nm to about 1,200 nm, from about 200 nm to about 500 nm, from about 200 nm to about 500 nm, from about 200 nm to about 900 nm, from about 200 nm to about 800 nm, from about 200 nm to about 700 nm, from about 200 nm to about 600 nm, About 400 nm to about 300 nm, about 400 nm to about 1,800 nm, about 500 nm to about 1,800 nm, about 600 nm to about 1,800 nm, about 700 nm to about 1,800 nm, about 800 nm About 1,800 nm to about 1,800 nm, about 1,300 nm to about 1,800 nm, about 1,400 nm to about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,000 nm to about 1,800 nm, about 1,100 nm to about 1,800 nm, about 400 nm to about 1,600 nm, about 400 nm to about 1,500 nm, about 400 nm to about 1,800 nm, about 1,500 nm to about 1,800 nm, about 1,600 nm to about 1,800 nm, about 1,700 nm to about 1,800 nm, From about 400 nm to about 1000 nm, from about 400 nm to about 900 nm, from about 400 nm to about 1,300 nm, from about 400 nm to about 1,200 nm, from about 400 nm to about 1,100 nm, from about 400 nm to about 600 nm, from about 400 nm to about 500 nm, from about 600 nm to about 1,600 nm, from about 700 nm to about 1,600 nm, from about 800 nm to about 800 nm, from about 400 nm to about 700 nm, About 1200 nm to about 1,600 nm, about 1,300 nm to about 1,600 nm, about 1,400 nm to about 1,600 nm, about 900 nm to about 1,600 nm, about 1,000 nm to about 1,600 nm, about 1,100 nm to about 1,600 nm, from about 600 nm to about 1500 nm, from about 600 nm to about 1,300 nm, from about 600 nm to about 1,200 nm, from about 600 nm to about 600 nm, and from about 600 nm to about 1, 500 nm to about 1,600 nm, from about 1,500 nm to about 1,600 nm, From about 600 nm to about 1000 nm, from about 600 nm to about 900 nm, from about 600 nm to about 800 nm, from about 600 nm to about 700 nm, from about 800 nm to about 1,400 nm, from about 900 nm to about 1,400 from about 1, 000 nm to about 1, 000 nm, from about 1,000 nm to about 1,400 nm, from about 1,100 nm to about 1,400 nm, from about 1,200 nm to about 1,400 nm, from about 1,300 nm to about 1,400 nm, From about 800 nm to about 1,100 nm, from about 800 nm to about 1,000 nm, or from about 800 nm to about 900 nm.

In one embodiment of the present invention, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part by weight to about 20 parts by weight. For example, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part to about 20 parts, from about 2 parts to about 20 parts, from about 3 parts to about 20 parts, From about 5 parts to about 20 parts by weight, from about 6 parts by weight to about 20 parts by weight, from about 7 parts by weight to about 20 parts by weight, from about 8 parts by weight to about 20 parts by weight, from about 9 From about 10 parts by weight to about 20 parts by weight, from about 11 parts by weight to about 20 parts by weight, from about 12 parts by weight to about 20 parts by weight, from about 13 parts by weight to about 20 parts by weight, from about 14 From about 15 parts by weight to about 20 parts by weight, from about 16 parts by weight to about 20 parts by weight, from about 17 parts by weight to about 20 parts by weight, from about 18 parts by weight to about 20 parts by weight, from about 19 to about 20 parts by weight, About 20 parts by weight, about 1 part by weight to about 19 parts by weight, about 1 part by weight to about 18 parts by weight, about 1 part by weight to about 17 parts by weight, about 1 part by weight to about 16 parts by weight, about 1 to about 15 parts by weight, about 1 to about 14 parts by weight, about 1 to about 13 parts by weight, about 1 to about 12 parts by weight, about 1 part by weight to about 11 parts by weight, about 1 to about 10 parts by weight, about 1 to about 9 parts by weight, about 1 to about 8 parts by weight, about 1 to about From about 1 part to about 3 parts by weight, or from about 1 part to about 5 parts by weight, from about 1 part by weight to about 6 parts by weight, from about 1 part by weight to about 5 parts by weight, from about 1 part by weight to about 4 parts by weight, About 2 parts by weight. When the content of the carbon structure is less than 1 part by weight with respect to 100 parts by weight of the hollow composite, the electric conductivity of the hollow composite may be lowered because the content of the carbon structure enabling easier electron transfer is small. If the content of the carbon structure is more than 20 parts by weight with respect to 100 parts by weight, the shape of the composite may not be induced into the hollow composite, and the shell may be thickened to lower the electrical conductivity.

In one embodiment herein, the charge transfer resistance of the hollow composite can be from about 10 [Omega] to about 200 k [Omega], but is not limited thereto. For example, the charge transfer resistances of the hollow composite may range from about 10 [Omega] to about 200 k [Omega], from about 100 [Omega] to about 200 k, from about 300 to about 200 k, from about 500 [ from about 10 kΩ to about 200 kΩ, from about 20 kΩ to about 200 kΩ, from about 30 kΩ to about 200 kΩ, from about 40 kΩ to about 200 kΩ, from about 50 kΩ to about 200 kΩ, From about 100 kΩ to about 200 kΩ, from about 120 kΩ to about 200 kΩ, from about 140 kΩ to about 200 kΩ, from about 60 kΩ to about 200 kΩ, from about 70 kΩ to about 200 kΩ, from about 80 kΩ to about 200 kΩ, from about 10 ohms to about 160 kilohms, from about 10 kilohms to about 140 kilohms, from about 10 ohms to about 200 kilohms, from about 160 kilohms to about 200 kilohms, from about 180 kilohms to about 200 kilohms, from about 10 kilohms to about 180 kilohms, From about 10 ohms to about 60 kilohms, from about 10 ohms to about 50 kilohms, from about 10 ohms to about 100 kilohms, from about 10 ohms to about 90 kilohms, from about 10 ohms to about 90 kilohangs, k < / RTI > From about 10 ohms to about 700 ohms, from about 10 ohms to about 500 ohms, from about 10 ohms to about 30 ohms, from about 10 ohms to about 20 kilohms, from about 10 ohms to about 10 kilohms, from about 10 ohms to about 1 kilohms, , From about 10 [Omega] to about 300 [Omega], or from about 10 [Omega] to about 100 [Omega]. The charge transfer resistance is closely related to the electrical conductivity of the hollow composite, and the lower the charge transfer resistance, the better the electrical conductivity of the hollow composite. The high electrical conductivity (low charge transfer resistance) of the hollow composite may be because the hollow composite comprises the carbon structure.

In one embodiment of the invention, the hollow composite can be used as a catalyst for an oxygen reduction reaction and can promote diffusion of oxygen, increase the number of active sites, and promote electrolyte diffusion for the oxygen reduction reaction.

In one embodiment of the present invention, the hollow composite may include the carbon structure to further enhance the weak electrical conductivity of the metal oxide.

According to a second aspect of the present invention, there is provided a method for producing a hollow composite according to the first aspect of the present invention, which comprises coating a polymer core with a mixed solution containing a precursor for a metal oxide and a precursor for a carbon structure, Shell composite, wherein the shell of the hollow composite comprises a hybrid comprising a metal oxide and a carbon structure, wherein the shell of the hollow composite comprises a metal oxide and a carbon structure, Wherein the hybrid is self-doped by a metal element contained in the metal oxide, and the first calcination is performed by heating the core-shell complex at a first temperature, And carbonizing and removing the particles to obtain the hollow composite.

Although the detailed description of the parts overlapping with the first aspect of the present application is omitted, the description of the first aspect of the present invention can be applied equally to the second aspect.

In one embodiment of the present invention, FIGS. 1A and 1B are a flow chart and a schematic view illustrating a process of manufacturing the hollow composite body, and a manufacturing process of the hollow composite body will be described with reference to FIGS. 1A and 1B. In step S100, a polymer core is coated using a mixed solution containing a precursor for a metal oxide and a precursor for a carbon structure to form a core-shell complex in which the precursor is coated on the polymer core particle.

In one embodiment of the present invention, the coating of the precursor for a metal oxide and the precursor for a carbon structure on the polymer core particles is carried out by an electrostatic action of the precursors contained in the polymer core particles, the metal oxide precursor and the precursor for the carbon structure It can be by interaction. For example, the coating may be due to the electrostatic interaction of the carbonyl groups of the polymer core particles with the hydroxyl groups contained in the metal oxide precursor and the precursor for the carbon structure.

In one embodiment of the present invention, the precursor for the metal oxide and the precursor for the carbon structure may be coated on the polymer core particle to modify the polymer core particle.

In one embodiment of the present invention, the precursor for the carbon structure may be about 1 part by weight to about 30 parts by weight based on 100 parts by weight of the mixed solution containing the metal oxide precursor and the precursor for the carbon structure, It is not. For example, the precursor for the carbon structure may be present in an amount of from about 1 part by weight to about 30 parts by weight, from about 2 parts by weight to about 30 parts by weight, from about 3 parts by weight to about 30 parts by weight, About 4 parts by weight to about 30 parts by weight, about 5 parts by weight to about 30 parts by weight, about 6 parts by weight to about 30 parts by weight, about 7 to about 30 parts by weight, about 8 to about 30 parts by weight, About 10 parts by weight to about 30 parts by weight, about 9 parts by weight to about 30 parts by weight, about 10 parts by weight to about 30 parts by weight, about 11 parts by weight to about 30 parts by weight, about 12 parts by weight to about 30 parts by weight, About 15 parts by weight to about 30 parts by weight, about 16 parts by weight to about 30 parts by weight, about 17 parts by weight to about 30 parts by weight, about 18 parts by weight to about 30 parts by weight, About 19 parts to about 30 parts, about 20 parts to about 30 parts, about 21 parts to about 30 parts, about 22 parts To about 30 parts by weight, from about 23 parts by weight to about 30 parts by weight, from about 24 parts by weight to about 30 parts by weight, from about 25 parts by weight to about 30 parts by weight, from about 26 parts by weight to about 30 parts by weight, About 30 parts by weight, about 28 parts by weight about 30 parts by weight, about 29 parts by weight about 30 parts by weight, about 1 part by about 29 parts by weight, about 1 part by about 28 parts by weight, about 1 part by weight About 1 part by weight to about 25 parts by weight, about 1 part by weight to about 24 parts by weight, about 1 to about 23 parts by weight, about 1 part by weight About 1 part by weight to about 20 parts by weight, about 1 part by weight to about 19 parts by weight, about 1 to about 18 parts by weight, about 1 part by weight From about 1 part by weight to about 15 parts by weight, from about 1 part by weight to about 14 parts by weight, from about 1 part by weight to about 1 part by weight, About 1 part by weight to about 12 parts by weight, about 1 to about 11 parts by weight, about 1 to about 10 parts by weight, about 1 to about 9 parts by weight, about 1 to about 1 part by weight, About 1 part to about 6 parts by weight, about 1 to about 5 parts by weight, about 1 to about 4 parts by weight, about 1 to about 7 parts by weight, About 3 parts by weight, or about 1 part by weight to about 2 parts by weight, but is not limited thereto.

In one embodiment of the invention, the size of the core-shell complex coated with the metal oxide precursor and the precursor for the carbon structure may be from about 50 nm to about 5,000 nm, but is not limited thereto. The size of the core-shell composite may vary depending on the shape of the core-shell composite. For example, when the core-shell complex is spherical, it means the diameter of the sphere. When the core-shell complex is elliptical, Lt; / RTI > The size of the core-shell complex can be, for example, from about 50 nm to about 5,000 nm, from about 100 nm to about 5,000 nm, from about 300 nm to about 5,000 nm, from about 500 nm to about 5,000 nm, 5,000 nm, from about 1,000 nm to about 5,000 nm, from about 1,300 nm to about 5,000 nm, from about 1,500 nm to about 5,000 nm, from about 1,700 nm to about 5,000 nm, from about 2,000 nm to about 5,000 nm, From about 3,000 nm to about 5,000 nm, from about 3,500 nm to about 5,000 nm, from about 4,000 nm to about 5,000 nm, from about 4,500 nm to about 5,000 nm, from about 50 nm to about 4,500 nm, from about 50 nm to about 4,000 nm, From about 50 nm to about 3,500 nm, from about 50 nm to about 3,000 nm, from about 50 nm to about 2,500 nm, from about 50 nm to about 2,000 nm, from about 50 nm to about 1,700 nm, from about 50 nm to about 1,500 nm, From about 50 nm to about 100 nm, from about 50 nm to about 100 nm, from about 50 nm to about 700 nm, from about 50 nm to about 500 nm, from about 50 nm to about 300 nm, From about 500 nm to about 4000 nm, from about 700 nm to about 4000 nm, from about 1,000 nm to about 4,000 nm, from about 1,300 nm to about 4,000 nm, from about 1,500 nm to about 4,000 nm, from about 2,000 nm to about 4,000 nm, from about 2,500 nm to about 4,000 nm, from about 3,000 nm to about 4,000 nm, from about 3,500 nm to about 4,000 nm, from about 100 nm to about 3,500 nm, From about 100 nm to about 1,500 nm, from about 100 nm to about 1,300 nm, from about 100 nm to about 3,000 nm, from about 100 nm to about 2,500 nm, from about 100 nm to about 2,000 nm, from about 100 nm to about 1,700 nm, from about 100 nm to about 500 nm, from about 100 nm to about 300 nm, from about 200 nm to about 2,000 nm, from about 300 nm to about 2,000 nm, from about 400 nm to about 1000 nm, from about 100 nm to about 700 nm, From about 500 nm to about 2,000 nm, from about 600 nm to about 2,000 nm, from about 700 nm to about 2,000 nm, from about 800 nm to about 2,000 nm, from about 900 nm to about 2,000 nm, From about 1,200 nm to about 2,000 nm, from about 1,200 nm to about 2,000 nm, from about 1,300 nm to about 2,000 nm, from about 1,400 nm to about 2,000 nm, from about 1,500 nm to about 2,000 nm, from about 1,600 nm to about 2,000 nm About 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 200 nm to about 1,700 nm, about 2,000 nm, about 1,700 nm to about 2,000 nm, about 1,800 nm to about 2,000 nm, about 1,900 nm to about 2,000 nm, About 200 nm to about 1,100 nm, about 200 nm to about 1,100 nm, about 200 nm to about 1,500 nm, about 200 nm to about 1,400 nm, about 200 nm to about 1,300 nm, about 200 nm to about 1,200 nm, From about 200 nm to about 600 nm, from about 200 nm to about 500 nm, from about 200 nm to about 1000 nm, from about 200 nm to about 900 nm, from about 200 nm to about 800 nm, from about 200 nm to about 700 nm, To about 400 nm, or from about 200 nm to about 300 nm, from about 400 nm to about 1,800 nm, from about 500 nm to about 1,800 nm, from about 600 nm to about 1,800 nm, from about 700 nm to about 1,800 nm, About 1,800 nm to about 1,800 nm, about 1,300 nm to about 1,800 nm, about 1,400 nm to about 1,800 nm, about 1,800 nm, about 900 nm to about 1,800 nm, about 1,000 nm to about 1,800 nm, about 1,100 nm to about 1,800 nm, From about 1,800 nm to about 1,800 nm, from about 1,500 nm to about 1,800 nm, from about 1,600 nm to about 1,800 nm, from about 1,700 nm to about 1,800 nm, from about 400 nm to about 1,700 nm, from about 400 nm to about 1,600 nm, About 400 nm to about 900 nm, about 400 nm to about 1,300 nm, about 400 nm to about 1,200 nm, about 400 nm to about 1,100 nm, about 400 nm to about 1,000 nm, about 400 nm to about 900 nm, From about 400 nm to about 800 nm, from about 400 nm to about 700 nm, from about 400 nm to about 600 nm, from about 400 nm to about 500 nm, from about 600 nm to about 1,600 nm, from about 700 nm to about 1,600 nm, To about 1,600 nm, from about 900 nm to about 1,600 nm, from about 1,000 nm to about 1,600 nm, from about 1,100 nm to about 1,600 nm, from about 1,200 nm to about 1,600 nm, from about 1,300 nm to about 1,600 nm, From about 600 nm to about 1500 nm, from about 600 nm to about 1,300 nm, from about 600 nm to about 1200 nm, from about 600 nm to about 1500 nm, from about 400 nm to about 1,600 nm, from about 1,500 nm to about 1,600 nm, from about 600 nm to about 700 nm, from about 800 nm to about 1,400 nm, from about 900 nm to about 800 nm, from about 600 nm to about 900 nm, from about 600 nm to about 900 nm, from about 600 nm to about 800 nm, From about 1, 000 nm to about 1, 400 nm, from about 1,000 nm to about 1,400 nm, from about 1,100 nm to about 1,400 nm, from about 1,200 nm to about 1,400 nm, from about 1,300 nm to about 1,400 nm, nm, from about 800 nm to about 1,100 nm, from about 800 nm to about 1,000 nm, or from about 800 nm to about 900 nm.

Subsequently, in step S200, by the first calcination, the polymer core particles of the core-shell composite are carbonized and removed so that the inner surface of the shell of the hollow composite is removed from the inner surface of the shell of the core- And carbon formed by carbonization of a surface functional group of the polymer core particle in contact with the metal core, wherein at least a part of metal cations of the metal oxide are reduced to form the metal element that self-dopes the hybrid.

In one embodiment of the invention, the first calcination may be performed at a temperature of about 400 < 0 > C to about 800 < 0 > C, but is not limited thereto. For example, the first calcination may be carried out at a temperature of about 400 ° C to about 800 ° C, about 450 ° C to about 800 ° C, about 500 ° C to about 800 ° C, about 550 ° C to about 800 ° C, From about 400 ° C to about 700 ° C, from about 400 ° C to about 650 ° C, from about 400 ° C to about 700 ° C, from about 650 ° C to about 800 ° C, from about 700 ° C to about 800 ° C, To about 600 ° C, from about 400 ° C to about 550 ° C, from about 400 ° C to about 500 ° C, or from about 400 ° C to about 450 ° C. When the first calcination is carried out at a temperature lower than 400 ° C., the polymer core particles may not be fully carbonized and removed. When the calcination is performed at a temperature higher than 800 ° C., the metal oxide is converted into a rutile crystal phase, And the hollow composite may be in an unstable state while the polymer core particles are carbonized and removed.

In one embodiment of the present invention, the content of the carbon structure may be reduced while the polymer core particles are carbonized and removed by the first calcination.

In one embodiment of the present invention, the carbon formed on the inner surface of the shell of the hollow composite may be, but is not limited to, form a layer having a thickness of about 1 nm to about 5 nm. For example, the carbon formed on the inner surface of the shell of the hollow composite may be about 1 nm to about 5 nm, about 2 nm to about 5 nm, about 3 nm to about 5 nm, about 4 nm to about 5 nm, nm to about 4 nm, from about 1 nm to about 3 nm, or from about 1 nm to about 2 nm thick.

The method further includes a second calcination step (S300) comprising heating the hollow composite obtained in the first calcination at a second temperature higher than the first temperature to crystallize the metal oxide contained in the hybrid, As shown in Fig.

In one embodiment of the invention, the second temperature at which the second calcination is performed may be performed at a temperature higher than the first temperature at which the first calcination is performed at about 500 ° C to about 850 ° C, It is not. For example, the second calcination may be conducted at a temperature of about 500 < 0 > C to about 850 [deg.] C, at about 550 [deg.] C to about 850 [deg.] C, at about 600 [deg.] C to about 850 [ From about 500 ° C to about 750 ° C, from about 500 ° C to about 700 ° C, from about 500 ° C to about 650 ° C, from about 500 ° C to about 700 ° C, from about 800 ° C to about 850 ° C, To about 600 < 0 > C, or from about 500 < 0 > C to about 550 < 0 > C. When the second calcination is carried out at a temperature lower than 500 ° C, the metal oxide may not crystallize. If the second calcination is carried out at a temperature higher than 850 ° C, the metal oxide may be converted into a rutile crystal phase, While the oxide is crystallized, the hollow composite may be in an unstable state.

In one embodiment herein, the hollow composite obtained by the steps S100 to S300 according to the second aspect of the present invention may have a size of from about 50 nm to about 5,000 nm. The size of the hollow composite may vary depending on the shape of the hollow composite. For example, in the case of a spherical shape, the diameter of the spherical hollow may be used, and in the case of an elliptical shape, the diameter of the long axial or short axis may be used. The size of the hollow complex can be, for example, from about 50 nm to about 5,000 nm, from about 100 nm to about 5,000 nm, from about 300 nm to about 5,000 nm, from about 500 nm to about 5,000 nm, from about 700 nm to about 5,000 nm From about 1,000 nm to about 5,000 nm, from about 1,300 nm to about 5,000 nm, from about 1,500 nm to about 5,000 nm, from about 1,700 nm to about 5,000 nm, from about 2,000 nm to about 5,000 nm, from about 2,500 nm to about 5,000 nm, From about 3,000 nm to about 5,000 nm, from about 3,500 nm to about 5,000 nm, from about 4,000 nm to about 5,000 nm, from about 4,500 nm to about 5,000 nm, from about 50 nm to about 4,500 nm, from about 50 nm to about 4,000 nm, From about 50 nm to about 1500 nm, from about 50 nm to about 3,000 nm, from about 50 nm to about 2,500 nm, from about 50 nm to about 2,000 nm, from about 50 nm to about 1,700 nm, from about 50 nm to about 1,500 nm, From about 50 nm to about 100 nm, from about 50 nm to about 100 nm, from about 50 nm to about 700 nm, from about 50 nm to about 500 nm, from about 50 nm to about 300 nm, from about 50 nm to about 100 nm, From about 500 nm to about 4000 nm, from about 700 nm to about 4000 nm, from about 1,000 nm to about 4,000 nm, from about 1,300 nm to about 4,000 nm, from about 1,500 nm to about 4,000 nm From about 2,000 nm to about 4,000 nm, from about 2,500 nm to about 4,000 nm, from about 3,000 nm to about 4,000 nm, from about 3,500 nm to about 4,000 nm, from about 100 nm to about 3,500 nm, From about 100 nm to about 1500 nm, from about 100 nm to about 1,300 nm, from about 100 nm to about 3,000 nm, from about 100 nm to about 2,500 nm, from about 100 nm to about 2,000 nm, from about 100 nm to about 1,700 nm, From about 100 nm to about 500 nm, from about 100 nm to about 300 nm, from about 200 nm to about 2,000 nm, from about 300 nm to about 2,000 nm, from about 400 nm to about 500 nm, From about 500 nm to about 2,000 nm, from about 600 nm to about 2,000 nm, from about 700 nm to about 2,000 nm, from about 800 nm to about 2,000 nm, from about 900 nm to about 2,000 nm, From about 1,200 nm to about 2,000 nm, from about 1,200 nm to about 2,000 nm, from about 1,300 nm to about 2,000 nm, from about 1,400 nm to about 2,000 nm, from about 1,500 nm to about 2,000 nm, from about 1,600 nm to about 2,000 nm about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 1,700 nm to about 2,000 nm, about 1,800 nm to about 2,000 nm, about 1,900 nm to about 2,000 nm, From about 200 nm to about 1,100 nm, from about 200 nm to about 1,100 nm, from about 200 nm to about 1,500 nm, from about 200 nm to about 1,400 nm, from about 200 nm to about 1,300 nm, from about 200 nm to about 1,200 nm, from about 200 nm to about 500 nm, from about 200 nm to about 500 nm, from about 200 nm to about 900 nm, from about 200 nm to about 800 nm, from about 200 nm to about 700 nm, from about 200 nm to about 600 nm, About 400 nm to about 300 nm, about 400 nm to about 1,800 nm, about 500 nm to about 1,800 nm, about 600 nm to about 1,800 nm, about 700 nm to about 1,800 nm, about 800 nm About 1,800 nm to about 1,800 nm, about 1,300 nm to about 1,800 nm, about 1,400 nm to about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,000 nm to about 1,800 nm, about 1,100 nm to about 1,800 nm, about 400 nm to about 1,600 nm, about 400 nm to about 1,500 nm, about 400 nm to about 1,800 nm, about 1,500 nm to about 1,800 nm, about 1,600 nm to about 1,800 nm, about 1,700 nm to about 1,800 nm, From about 400 nm to about 1000 nm, from about 400 nm to about 900 nm, from about 400 nm to about 1,300 nm, from about 400 nm to about 1,200 nm, from about 400 nm to about 1,100 nm, from about 400 nm to about 600 nm, from about 400 nm to about 500 nm, from about 600 nm to about 1,600 nm, from about 700 nm to about 1,600 nm, from about 800 nm to about 800 nm, from about 400 nm to about 700 nm, About 1200 nm to about 1,600 nm, about 1,300 nm to about 1,600 nm, about 1,400 nm to about 1,600 nm, about 900 nm to about 1,600 nm, about 1,000 nm to about 1,600 nm, about 1,100 nm to about 1,600 nm, from about 600 nm to about 1500 nm, from about 600 nm to about 1,300 nm, from about 600 nm to about 1,200 nm, from about 600 nm to about 600 nm, and from about 600 nm to about 1, 500 nm to about 1,600 nm, from about 1,500 nm to about 1,600 nm, From about 600 nm to about 1000 nm, from about 600 nm to about 900 nm, from about 600 nm to about 800 nm, from about 600 nm to about 700 nm, from about 800 nm to about 1,400 nm, from about 900 nm to about 1,400 from about 1, 000 nm to about 1, 000 nm, from about 1,000 nm to about 1,400 nm, from about 1,100 nm to about 1,400 nm, from about 1,200 nm to about 1,400 nm, from about 1,300 nm to about 1,400 nm, From about 800 nm to about 1,100 nm, from about 800 nm to about 1,000 nm, or from about 800 nm to about 900 nm.

In one embodiment herein, the size of the hollow composite after the first calcination and the second calcination is between about 5% and about 40%, relative to the size of the core-shell composite during the subsequent first and second calcinations, But it is not limited thereto. For example, the size of the hollow composite with respect to the size of the core-shell composite by the first and second calcinations may range from about 5% to about 40%, from about 10% to about 40%, from about 15% to about About 30% to about 40%, about 35% to about 40%, about 5% to about 35%, about 5% to about 30% , About 5% to about 25%, about 5% to about 20%, about 5% to about 15%, or about 5% to about 10% The size shrinkage of the hollow composite may be due to the condensation / polymerization of the template associated with the sintering shrinkage of the metal oxide during the first calcination and the second calcination.

In one embodiment of the present invention, the metal oxide may include a semiconductor oxide, for example, TiO ₂ , SnO ₂ , ZnO, VO ₂ , In ₂ O ₃ , NiO, MoO ₃ , SrTiO ₃ , Fe-doped SrTiO ₃ , Fe ₂ O ₃ , WO ₃ , CuO, BiVO ₄ , And combinations of these. ≪ RTI ID = 0.0 > [0040] < / RTI >

In one embodiment, the carbon structure is selected from the group consisting of reduced graphene oxide (rGO), graphene, graphite, single wall carbon nanotubes, multiwall carbon nanotubes, carbon nanohorns, Synthetic carbon sources including acetylene black, carbon black formed from the combustion of hydrocarbons or polymers (for example, Kecheon black), and carbon black And a carbon structure selected from the group consisting of combinations thereof.

In one embodiment of the present invention, the metal element may be in a reduced state than the metal cation contained in the metal oxide. The reduced metal cation is in a reduced state and is unstable and prone to oxidation. However, the carbon formed on the inner surface of the shell and the reduced metal cation are stabilized by the carbon structure to self-dope the hybrid. For example, if the metal oxide contained in the shell include TiO _2, the Ti ^{4 +} contained in the TiO ₂ is partially reduced to the Ti ^{3 +} the Ti ^{3 +} in the hollow composite stabilization of the hollow composite Became The hybrids can be self-doped by the stabilized Ti ³⁺ .

In one embodiment of the present invention, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part by weight to about 20 parts by weight. For example, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part to about 20 parts, from about 2 parts to about 20 parts, from about 3 parts to about 20 parts, From about 5 parts to about 20 parts by weight, from about 6 parts by weight to about 20 parts by weight, from about 7 parts by weight to about 20 parts by weight, from about 8 parts by weight to about 20 parts by weight, from about 9 From about 10 parts by weight to about 20 parts by weight, from about 11 parts by weight to about 20 parts by weight, from about 12 parts by weight to about 20 parts by weight, from about 13 parts by weight to about 20 parts by weight, from about 14 From about 15 parts by weight to about 20 parts by weight, from about 16 parts by weight to about 20 parts by weight, from about 17 parts by weight to about 20 parts by weight, from about 18 parts by weight to about 20 parts by weight, from about 19 to about 20 parts by weight, About 20 parts by weight, about 1 part by weight to about 19 parts by weight, about 1 part by weight to about 18 parts by weight, about 1 part by weight to about 17 parts by weight, about 1 part by weight to about 16 parts by weight, about 1 to about 15 parts by weight, about 1 to about 14 parts by weight, about 1 to about 13 parts by weight, about 1 to about 12 parts by weight, about 1 part by weight to about 11 parts by weight, about 1 to about 10 parts by weight, about 1 to about 9 parts by weight, about 1 to about 8 parts by weight, about 1 to about From about 1 part to about 3 parts by weight, or from about 1 part to about 5 parts by weight, from about 1 part by weight to about 6 parts by weight, from about 1 part by weight to about 5 parts by weight, from about 1 part by weight to about 4 parts by weight, About 2 parts by weight. When the content of the carbon structure is less than 1 part by weight with respect to 100 parts by weight of the hollow composite, the electric conductivity of the hollow composite may be lowered because the content of the carbon structure enabling easier electron transfer is small. If the content of the carbon structure is more than 20 parts by weight with respect to 100 parts by weight, the shape of the composite may not be induced into the hollow composite, and the shell may be thickened to lower the electrical conductivity.

In one embodiment of the invention, the hollow composite can be used as a catalyst for an oxygen reduction reaction and can promote diffusion of oxygen, increase the number of active sites, and promote electrolyte diffusion for the oxygen reduction reaction.

In one embodiment of the present invention, the hollow composite may include the carbon structure to further enhance the weak electrical conductivity of the metal oxide.

A third aspect of the invention provides an electrocatalyst comprising a hollow composite according to the first aspect of the present invention. Wherein the hollow composite comprises a shell comprising a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid is self-doped by a metal element contained in the metal oxide, The inner surface of the shell of the composite contains carbon.

In one embodiment of the invention, the electrocatalyst may be for an oxygen reduction reaction.

A fourth aspect of the invention provides an electrode comprising a hollow composite according to the first aspect of the present application.

In one embodiment of the invention, the electrode may be for an oxygen reduction reaction.

A fifth aspect of the invention provides a cell comprising an electrode according to the fourth aspect of the present application.

Although the detailed description of the parts overlapping with the first aspect and the second aspect of the present application is omitted, the contents of the first and second aspects of the present invention are the same as those of the third aspect, the fourth aspect, and the fifth aspect, Even if the explanation is omitted, the same can be applied.

Hereinafter, the third aspect, the fourth aspect, and the fifth aspect of the present application will be described in detail.

In one embodiment of the invention, the battery may be a fuel cell or a secondary battery, but is not limited thereto. For example, the secondary battery may be a metal-air battery, but is not limited thereto.

In one embodiment of the present application, when the battery is a fuel cell, the fuel cell is an electrochemical device that directly converts the chemical energy of the fuel into electrical energy, potentially providing a clean and highly efficient source of electrical vehicle power do. The fuel cell system may be a solid oxide fuel cell, but is not limited thereto. The fuel cell system may include, but is not limited to, an electrolyte membrane, a first electrode, and a second electrode.

In one embodiment, the first electrode and / or the second electrode may be a glass carbon electrode or a rotating disk electrode, and the material of the electrode may be carbon, a metal, a metal oxide, a conductive polymer, But are not limited to, those selected from the group consisting of < RTI ID = 0.0 >

In one embodiment of the present invention, the electrochemical reaction of the fuel cell system may proceed in a direction opposite to that of the water decomposition system, wherein positive ions are generated by the oxidation reaction of hydrogen at the first electrode, Water may be generated by a reduction reaction, but is not limited thereto. Electrons are generated in the first electrode and electrons are consumed in the second electrode, so that electricity may flow when the first electrode and the second electrode are connected, but the present invention is not limited thereto.

In one embodiment, the first electrode and the second electrode may each comprise a semiconductor or a conductive material, and the second electrode comprises a hollow composite according to the first aspect of the present invention for an oxygen reduction reaction Electrode.

In one embodiment of the present invention, the electrolyte membrane may include a proton-conducting polymer membrane, and the first electrode and the second electrode may be separated from each other and a proton flow may be formed between the electrodes, , ≪ / RTI > for example, Nafion.

In one embodiment of the present invention, in order to allow the oxidation and reduction reactions to proceed at a high rate of reaction in the fuel cell system and to allow the reaction to proceed at a reduced potential, the hollow composite according to the first aspect of the invention May be used as the second electrode. In the electrode including the hollow composite, the hollow composite acts as an electrocatalyst for an oxygen reduction reaction, thereby improving electrocatalytic activity by increasing the number of active sites in an oxygen reduction reaction, improving durability in an alkaline medium, Can be improved.

In one embodiment of the invention, the hollow composite comprises a shell comprising a hybrid comprising a metal oxide and a carbon structure, wherein the hybrid is self-doped by a metal element contained in the metal oxide -doping), and the inner surface of the shell of the hollow composite may comprise carbon.

In one embodiment of the present invention, the metal oxide may include a semiconductor oxide, for example, TiO ₂ , SnO ₂ , ZnO, VO ₂ , In ₂ O ₃ , NiO, MoO ₃ , SrTiO ₃ , Fe-doped SrTiO ₃ , Fe ₂ O ₃ , WO ₃ , CuO, BiVO ₄ , And combinations of these. ≪ RTI ID = 0.0 > [0040] < / RTI >

In one embodiment, the carbon structure is selected from the group consisting of reduced graphene oxide (rGO), graphene, graphite, single wall carbon nanotubes, multiwall carbon nanotubes, carbon nanohorns, Synthetic carbon sources including acetylene black, carbon black formed from the combustion of hydrocarbons or polymers (for example, Kecheon black), and carbon black And a carbon structure selected from the group consisting of combinations thereof.

In one embodiment of the present invention, the metal element may be in a reduced state than the metal cation contained in the metal oxide. The reduced metal cation is in a reduced state and is unstable and prone to oxidation. However, the carbon formed on the inner surface of the shell and the reduced metal cation are stabilized by the carbon structure to self-dope the hybrid. For example, if the metal oxide contained in the shell include TiO _2, the Ti ^{4 +} contained in the TiO ₂ is partially reduced to the Ti ^{3 +} the Ti ^{3 +} in the hollow composite stabilization of the hollow composite Became The hybrids can be self-doped by the stabilized Ti ³⁺ .

In one embodiment herein, the size of the hollow composite can be from about 50 nm to about 5,000 nm. The size of the hollow composite may vary depending on the shape of the hollow composite. For example, in the case of a spherical shape, the diameter of the spherical hollow may be used, and in the case of an elliptical shape, the diameter of the long axial or short axis may be used. The size of the hollow complex can be, for example, from about 50 nm to about 5,000 nm, from about 100 nm to about 5,000 nm, from about 300 nm to about 5,000 nm, from about 500 nm to about 5,000 nm, from about 700 nm to about 5,000 nm From about 1,000 nm to about 5,000 nm, from about 1,300 nm to about 5,000 nm, from about 1,500 nm to about 5,000 nm, from about 1,700 nm to about 5,000 nm, from about 2,000 nm to about 5,000 nm, from about 2,500 nm to about 5,000 nm, From about 3,000 nm to about 5,000 nm, from about 3,500 nm to about 5,000 nm, from about 4,000 nm to about 5,000 nm, from about 4,500 nm to about 5,000 nm, from about 50 nm to about 4,500 nm, from about 50 nm to about 4,000 nm, From about 50 nm to about 1500 nm, from about 50 nm to about 3,000 nm, from about 50 nm to about 2,500 nm, from about 50 nm to about 2,000 nm, from about 50 nm to about 1,700 nm, from about 50 nm to about 1,500 nm, From about 50 nm to about 100 nm, from about 50 nm to about 100 nm, from about 50 nm to about 700 nm, from about 50 nm to about 500 nm, from about 50 nm to about 300 nm, from about 50 nm to about 100 nm, From about 500 nm to about 4000 nm, from about 700 nm to about 4000 nm, from about 1,000 nm to about 4,000 nm, from about 1,300 nm to about 4,000 nm, from about 1,500 nm to about 4,000 nm From about 2,000 nm to about 4,000 nm, from about 2,500 nm to about 4,000 nm, from about 3,000 nm to about 4,000 nm, from about 3,500 nm to about 4,000 nm, from about 100 nm to about 3,500 nm, From about 100 nm to about 1500 nm, from about 100 nm to about 1,300 nm, from about 100 nm to about 3,000 nm, from about 100 nm to about 2,500 nm, from about 100 nm to about 2,000 nm, from about 100 nm to about 1,700 nm, From about 100 nm to about 500 nm, from about 100 nm to about 300 nm, from about 200 nm to about 2,000 nm, from about 300 nm to about 2,000 nm, from about 400 nm to about 500 nm, From about 500 nm to about 2,000 nm, from about 600 nm to about 2,000 nm, from about 700 nm to about 2,000 nm, from about 800 nm to about 2,000 nm, from about 900 nm to about 2,000 nm, From about 1,200 nm to about 2,000 nm, from about 1,200 nm to about 2,000 nm, from about 1,300 nm to about 2,000 nm, from about 1,400 nm to about 2,000 nm, from about 1,500 nm to about 2,000 nm, from about 1,600 nm to about 2,000 nm about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 1,700 nm to about 2,000 nm, about 1,800 nm to about 2,000 nm, about 1,900 nm to about 2,000 nm, From about 200 nm to about 1,100 nm, from about 200 nm to about 1,100 nm, from about 200 nm to about 1,500 nm, from about 200 nm to about 1,400 nm, from about 200 nm to about 1,300 nm, from about 200 nm to about 1,200 nm, from about 200 nm to about 500 nm, from about 200 nm to about 500 nm, from about 200 nm to about 900 nm, from about 200 nm to about 800 nm, from about 200 nm to about 700 nm, from about 200 nm to about 600 nm, About 400 nm to about 300 nm, about 400 nm to about 1,800 nm, about 500 nm to about 1,800 nm, about 600 nm to about 1,800 nm, about 700 nm to about 1,800 nm, about 800 nm About 1,800 nm to about 1,800 nm, about 1,300 nm to about 1,800 nm, about 1,400 nm to about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,000 nm to about 1,800 nm, about 1,100 nm to about 1,800 nm, about 400 nm to about 1,600 nm, about 400 nm to about 1,500 nm, about 400 nm to about 1,800 nm, about 1,500 nm to about 1,800 nm, about 1,600 nm to about 1,800 nm, about 1,700 nm to about 1,800 nm, From about 400 nm to about 1000 nm, from about 400 nm to about 900 nm, from about 400 nm to about 1,300 nm, from about 400 nm to about 1,200 nm, from about 400 nm to about 1,100 nm, from about 400 nm to about 600 nm, from about 400 nm to about 500 nm, from about 600 nm to about 1,600 nm, from about 700 nm to about 1,600 nm, from about 800 nm to about 800 nm, from about 400 nm to about 700 nm, About 1200 nm to about 1,600 nm, about 1,300 nm to about 1,600 nm, about 1,400 nm to about 1,600 nm, about 900 nm to about 1,600 nm, about 1,000 nm to about 1,600 nm, about 1,100 nm to about 1,600 nm, from about 600 nm to about 1500 nm, from about 600 nm to about 1,300 nm, from about 600 nm to about 1,200 nm, from about 600 nm to about 600 nm, and from about 600 nm to about 1, 500 nm to about 1,600 nm, from about 1,500 nm to about 1,600 nm, From about 600 nm to about 1000 nm, from about 600 nm to about 900 nm, from about 600 nm to about 800 nm, from about 600 nm to about 700 nm, from about 800 nm to about 1,400 nm, from about 900 nm to about 1,400 from about 1, 000 nm to about 1, 000 nm, from about 1,000 nm to about 1,400 nm, from about 1,100 nm to about 1,400 nm, from about 1,200 nm to about 1,400 nm, from about 1,300 nm to about 1,400 nm, From about 800 nm to about 1,100 nm, from about 800 nm to about 1,000 nm, or from about 800 nm to about 900 nm.

In one embodiment of the present invention, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part by weight to about 20 parts by weight. For example, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part to about 20 parts, from about 2 parts to about 20 parts, from about 3 parts to about 20 parts, From about 5 parts to about 20 parts by weight, from about 6 parts by weight to about 20 parts by weight, from about 7 parts by weight to about 20 parts by weight, from about 8 parts by weight to about 20 parts by weight, from about 9 From about 10 parts by weight to about 20 parts by weight, from about 11 parts by weight to about 20 parts by weight, from about 12 parts by weight to about 20 parts by weight, from about 13 parts by weight to about 20 parts by weight, from about 14 From about 15 parts by weight to about 20 parts by weight, from about 16 parts by weight to about 20 parts by weight, from about 17 parts by weight to about 20 parts by weight, from about 18 parts by weight to about 20 parts by weight, from about 19 to about 20 parts by weight, About 20 parts by weight, about 1 part by weight to about 19 parts by weight, about 1 part by weight to about 18 parts by weight, about 1 part by weight to about 17 parts by weight, about 1 part by weight to about 16 parts by weight, about 1 to about 15 parts by weight, about 1 to about 14 parts by weight, about 1 to about 13 parts by weight, about 1 to about 12 parts by weight, about 1 part by weight to about 11 parts by weight, about 1 to about 10 parts by weight, about 1 to about 9 parts by weight, about 1 to about 8 parts by weight, about 1 to about From about 1 part to about 3 parts by weight, or from about 1 part to about 5 parts by weight, from about 1 part by weight to about 6 parts by weight, from about 1 part by weight to about 5 parts by weight, from about 1 part by weight to about 4 parts by weight, About 2 parts by weight. When the content of the carbon structure is less than 1 part by weight with respect to 100 parts by weight of the hollow composite, the electric conductivity of the hollow composite may be lowered because the content of the carbon structure enabling easier electron transfer is small. If the content of the carbon structure is more than 20 parts by weight with respect to 100 parts by weight, the shape of the composite may not be induced into the hollow composite, and the shell may be thickened to lower the electrical conductivity.

In one embodiment herein, the charge transfer resistance of the hollow composite can be from about 10 [Omega] to about 200 k [Omega], but is not limited thereto. For example, the charge transfer resistances of the hollow composite may range from about 10 [Omega] to about 200 k [Omega], from about 100 [Omega] to about 200 k, from about 300 to about 200 k, from about 500 [ from about 10 kΩ to about 200 kΩ, from about 20 kΩ to about 200 kΩ, from about 30 kΩ to about 200 kΩ, from about 40 kΩ to about 200 kΩ, from about 50 kΩ to about 200 kΩ, From about 100 kΩ to about 200 kΩ, from about 120 kΩ to about 200 kΩ, from about 140 kΩ to about 200 kΩ, from about 60 kΩ to about 200 kΩ, from about 70 kΩ to about 200 kΩ, from about 80 kΩ to about 200 kΩ, from about 10 ohms to about 160 kilohms, from about 10 kilohms to about 140 kilohms, from about 10 ohms to about 200 kilohms, from about 160 kilohms to about 200 kilohms, from about 180 kilohms to about 200 kilohms, from about 10 kilohms to about 180 kilohms, From about 10 ohms to about 60 kilohms, from about 10 ohms to about 50 kilohms, from about 10 ohms to about 100 kilohms, from about 10 ohms to about 90 kilohms, from about 10 ohms to about 90 kilohangs, k < / RTI > From about 10 ohms to about 700 ohms, from about 10 ohms to about 500 ohms, from about 10 ohms to about 30 ohms, from about 10 ohms to about 20 kilohms, from about 10 ohms to about 10 kilohms, from about 10 ohms to about 1 kilohms, , From about 10 [Omega] to about 300 [Omega], or from about 10 [Omega] to about 100 [Omega]. The charge transfer resistance is closely related to the electrical conductivity of the hollow composite, and the lower the charge transfer resistance, the better the electrical conductivity of the hollow composite. The high electrical conductivity (low charge transfer resistance) of the hollow composite may be because the hollow composite comprises the carbon structure.

In one embodiment of the invention, the hollow composite can be used as a catalyst for an oxygen reduction reaction and can promote diffusion of oxygen, increase the number of active sites, and promote electrolyte diffusion for the oxygen reduction reaction.

In one embodiment of the present invention, the hollow composite may include the carbon structure to further enhance the weak electrical conductivity of the metal oxide.

A sixth aspect of the invention provides an electronic ink comprising a hollow composite according to the first aspect of the present application. A seventh aspect of the present invention provides an electronic paper or display device comprising electronic ink according to the sixth aspect of the present application.

Although the description of the first to fifth aspects of the present application is omitted from the sixth aspect of the present application and the seventh aspect of the present application, the same can be applied.

Hereinafter, the sixth and seventh aspects of the present application will be described in detail.

The electronic paper is a display device for displaying characters or images using a flexible substrate, and can be used for reproducing millions of times.

The display device using the electronic paper distributes conductive fine particles between the flexible substrates and then displays data by changing the direction of the fine particles (or charged particles) according to the polarity of the electromagnetic field. Since the electronic paper is a reflective type that does not use a separate light source, its production cost is lower than that of a conventional flat panel display panel, and power consumption is low because background lighting and continuous recharging are not required like a liquid crystal display device. In addition, the electronic paper is excellent in sharpness, has a wide viewing angle, and retains its previous state due to the internal balance of positively or negatively charged particles. Therefore, the electronic paper has a memory function that does not disappear without power.

The electronic paper can be implemented on a substrate or a flexible substrate selected from the group consisting of various substrates, for example, plastic, metal, paper, and combinations thereof, and can be implemented in a large area Therefore, it is possible to mass-produce by a roll-to-roll process using a flexible substrate.

The electronic paper may include, but is not limited to, a lower substrate and an upper substrate disposed to face each other at regular intervals, and a display portion between the lower substrate and the upper substrate.

The display unit may include barrier ribs for separating unit pixels for determining resolution, lower electrodes separately provided for each barrier, an electronic ink layer formed on the lower electrode, and an upper electrode formed on the electron ink layer. But is not limited thereto.

Wherein the electronic ink layer comprises a film and an encapsulated ink capsule dispersed in the film, each ink capsule comprising an inorganic or organic fluid colored in a transparent or arbitrary color, and a light- , And particles having an anode that does not transmit light. For example, when the ink capsule includes negatively charged black particles and positively charged white particles, if positive voltage is applied to the upper electrode and negative voltage is applied to the lower electrode, Negatively charged black particles are arranged and positively charged white particles are arranged on the lower electrode, so that the electronic paper screen can display black.

In one embodiment of the invention, the negatively charged particles and / or the positively charged particles may comprise a hollow composite according to the first aspect of the present invention.

In one embodiment of the invention, the hollow composite used as the negatively charged particles and / or the positively charged particles comprises a shell comprising a hybrid comprising a metal oxide and a carbon structure, Doped with a metal element contained in the metal oxide, and the inner surface of the shell of the hollow composite may include carbon.

In one embodiment of the present invention, the metal oxide may include a semiconductor oxide, for example, TiO ₂ , SnO ₂ , ZnO, VO ₂ , In ₂ O ₃ , NiO, MoO ₃ , SrTiO ₃ , Fe-doped SrTiO ₃ , Fe ₂ O ₃ , WO ₃ , CuO, BiVO ₄ , And combinations of these. ≪ RTI ID = 0.0 > [0040] < / RTI >

In one embodiment, the carbon structure is selected from the group consisting of reduced graphene oxide (rGO), graphene, graphite, single wall carbon nanotubes, multiwall carbon nanotubes, carbon nanohorns, Synthetic carbon sources including acetylene black, carbon black formed from the combustion of hydrocarbons or polymers (for example, Kecheon black), and carbon black And a carbon structure selected from the group consisting of combinations thereof.

In one embodiment of the present invention, the metal element may be in a reduced state than the metal cation contained in the metal oxide. The reduced metal cation is in a reduced state and is unstable and prone to oxidation. However, the carbon formed on the inner surface of the shell and the reduced metal cation are stabilized by the carbon structure to self-dope the hybrid. For example, if the metal oxide contained in the shell include TiO _2, the Ti ^{4 +} contained in the TiO ₂ is partially reduced to the Ti ^{3 +} the Ti ^{3 +} in the hollow composite stabilization of the hollow composite Became The hybrids can be self-doped by the stabilized Ti ³⁺ .

In one embodiment herein, the size of the hollow composite can be from about 50 nm to about 5,000 nm. The size of the hollow composite may vary depending on the shape of the hollow composite. For example, in the case of a spherical shape, the diameter of the spherical hollow may be used, and in the case of an elliptical shape, the diameter of the long axial or short axis may be used. The size of the hollow complex can be, for example, from about 50 nm to about 5,000 nm, from about 100 nm to about 5,000 nm, from about 300 nm to about 5,000 nm, from about 500 nm to about 5,000 nm, from about 700 nm to about 5,000 nm From about 1,000 nm to about 5,000 nm, from about 1,300 nm to about 5,000 nm, from about 1,500 nm to about 5,000 nm, from about 1,700 nm to about 5,000 nm, from about 2,000 nm to about 5,000 nm, from about 2,500 nm to about 5,000 nm, From about 3,000 nm to about 5,000 nm, from about 3,500 nm to about 5,000 nm, from about 4,000 nm to about 5,000 nm, from about 4,500 nm to about 5,000 nm, from about 50 nm to about 4,500 nm, from about 50 nm to about 4,000 nm, From about 50 nm to about 1500 nm, from about 50 nm to about 3,000 nm, from about 50 nm to about 2,500 nm, from about 50 nm to about 2,000 nm, from about 50 nm to about 1,700 nm, from about 50 nm to about 1,500 nm, From about 50 nm to about 100 nm, from about 50 nm to about 100 nm, from about 50 nm to about 700 nm, from about 50 nm to about 500 nm, from about 50 nm to about 300 nm, from about 50 nm to about 100 nm, From about 500 nm to about 4000 nm, from about 700 nm to about 4000 nm, from about 1,000 nm to about 4,000 nm, from about 1,300 nm to about 4,000 nm, from about 1,500 nm to about 4,000 nm From about 2,000 nm to about 4,000 nm, from about 2,500 nm to about 4,000 nm, from about 3,000 nm to about 4,000 nm, from about 3,500 nm to about 4,000 nm, from about 100 nm to about 3,500 nm, From about 100 nm to about 1500 nm, from about 100 nm to about 1,300 nm, from about 100 nm to about 3,000 nm, from about 100 nm to about 2,500 nm, from about 100 nm to about 2,000 nm, from about 100 nm to about 1,700 nm, From about 100 nm to about 500 nm, from about 100 nm to about 300 nm, from about 200 nm to about 2,000 nm, from about 300 nm to about 2,000 nm, from about 400 nm to about 500 nm, From about 500 nm to about 2,000 nm, from about 600 nm to about 2,000 nm, from about 700 nm to about 2,000 nm, from about 800 nm to about 2,000 nm, from about 900 nm to about 2,000 nm, From about 1,200 nm to about 2,000 nm, from about 1,200 nm to about 2,000 nm, from about 1,300 nm to about 2,000 nm, from about 1,400 nm to about 2,000 nm, from about 1,500 nm to about 2,000 nm, from about 1,600 nm to about 2,000 nm about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 200 nm to about 1,800 nm, about 1,700 nm to about 2,000 nm, about 1,800 nm to about 2,000 nm, about 1,900 nm to about 2,000 nm, From about 200 nm to about 1,100 nm, from about 200 nm to about 1,100 nm, from about 200 nm to about 1,500 nm, from about 200 nm to about 1,400 nm, from about 200 nm to about 1,300 nm, from about 200 nm to about 1,200 nm, from about 200 nm to about 500 nm, from about 200 nm to about 500 nm, from about 200 nm to about 900 nm, from about 200 nm to about 800 nm, from about 200 nm to about 700 nm, from about 200 nm to about 600 nm, About 400 nm to about 300 nm, about 400 nm to about 1,800 nm, about 500 nm to about 1,800 nm, about 600 nm to about 1,800 nm, about 700 nm to about 1,800 nm, about 800 nm About 1,800 nm to about 1,800 nm, about 1,300 nm to about 1,800 nm, about 1,400 nm to about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,800 nm, about 1,000 nm to about 1,800 nm, about 1,100 nm to about 1,800 nm, about 400 nm to about 1,600 nm, about 400 nm to about 1,500 nm, about 400 nm to about 1,800 nm, about 1,500 nm to about 1,800 nm, about 1,600 nm to about 1,800 nm, about 1,700 nm to about 1,800 nm, From about 400 nm to about 1000 nm, from about 400 nm to about 900 nm, from about 400 nm to about 1,300 nm, from about 400 nm to about 1,200 nm, from about 400 nm to about 1,100 nm, from about 400 nm to about 600 nm, from about 400 nm to about 500 nm, from about 600 nm to about 1,600 nm, from about 700 nm to about 1,600 nm, from about 800 nm to about 800 nm, from about 400 nm to about 700 nm, About 1200 nm to about 1,600 nm, about 1,300 nm to about 1,600 nm, about 1,400 nm to about 1,600 nm, about 900 nm to about 1,600 nm, about 1,000 nm to about 1,600 nm, about 1,100 nm to about 1,600 nm, from about 600 nm to about 1500 nm, from about 600 nm to about 1,300 nm, from about 600 nm to about 1,200 nm, from about 600 nm to about 600 nm, and from about 600 nm to about 1, 500 nm to about 1,600 nm, from about 1,500 nm to about 1,600 nm, From about 600 nm to about 1000 nm, from about 600 nm to about 900 nm, from about 600 nm to about 800 nm, from about 600 nm to about 700 nm, from about 800 nm to about 1,400 nm, from about 900 nm to about 1,400 from about 1, 000 nm to about 1, 000 nm, from about 1,000 nm to about 1,400 nm, from about 1,100 nm to about 1,400 nm, from about 1,200 nm to about 1,400 nm, from about 1,300 nm to about 1,400 nm, From about 800 nm to about 1,100 nm, from about 800 nm to about 1,000 nm, or from about 800 nm to about 900 nm.

In one embodiment of the present invention, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part by weight to about 20 parts by weight. For example, the content of the carbon structure relative to 100 parts by weight of the hollow composite may be from about 1 part to about 20 parts, from about 2 parts to about 20 parts, from about 3 parts to about 20 parts, From about 5 parts to about 20 parts by weight, from about 6 parts by weight to about 20 parts by weight, from about 7 parts by weight to about 20 parts by weight, from about 8 parts by weight to about 20 parts by weight, from about 9 From about 10 parts by weight to about 20 parts by weight, from about 11 parts by weight to about 20 parts by weight, from about 12 parts by weight to about 20 parts by weight, from about 13 parts by weight to about 20 parts by weight, from about 14 From about 15 parts by weight to about 20 parts by weight, from about 16 parts by weight to about 20 parts by weight, from about 17 parts by weight to about 20 parts by weight, from about 18 parts by weight to about 20 parts by weight, from about 19 to about 20 parts by weight, About 20 parts by weight, about 1 part by weight to about 19 parts by weight, about 1 part by weight to about 18 parts by weight, about 1 part by weight to about 17 parts by weight, about 1 part by weight to about 16 parts by weight, about 1 to about 15 parts by weight, about 1 to about 14 parts by weight, about 1 to about 13 parts by weight, about 1 to about 12 parts by weight, about 1 part by weight to about 11 parts by weight, about 1 to about 10 parts by weight, about 1 to about 9 parts by weight, about 1 to about 8 parts by weight, about 1 to about From about 1 part to about 3 parts by weight, or from about 1 part to about 5 parts by weight, from about 1 part by weight to about 6 parts by weight, from about 1 part by weight to about 5 parts by weight, from about 1 part by weight to about 4 parts by weight, About 2 parts by weight. When the content of the carbon structure is less than 1 part by weight with respect to 100 parts by weight of the hollow composite, the electric conductivity of the hollow composite may be lowered because the content of the carbon structure enabling easier electron transfer is small. If the content of the carbon structure is more than 20 parts by weight with respect to 100 parts by weight, the shape of the composite may not be induced into the hollow composite, and the shell may be thickened to lower the electrical conductivity.

In one embodiment herein, the charge transfer resistance of the hollow composite can be from about 10 [Omega] to about 200 k [Omega], but is not limited thereto. For example, the charge transfer resistances of the hollow composite may range from about 10 [Omega] to about 200 k [Omega], from about 100 [Omega] to about 200 k, from about 300 to about 200 k, from about 500 [ from about 10 kΩ to about 200 kΩ, from about 20 kΩ to about 200 kΩ, from about 30 kΩ to about 200 kΩ, from about 40 kΩ to about 200 kΩ, from about 50 kΩ to about 200 kΩ, From about 100 kΩ to about 200 kΩ, from about 120 kΩ to about 200 kΩ, from about 140 kΩ to about 200 kΩ, from about 60 kΩ to about 200 kΩ, from about 70 kΩ to about 200 kΩ, from about 80 kΩ to about 200 kΩ, from about 10 ohms to about 160 kilohms, from about 10 kilohms to about 140 kilohms, from about 10 ohms to about 200 kilohms, from about 160 kilohms to about 200 kilohms, from about 180 kilohms to about 200 kilohms, from about 10 kilohms to about 180 kilohms, From about 10 ohms to about 60 kilohms, from about 10 ohms to about 50 kilohms, from about 10 ohms to about 100 kilohms, from about 10 ohms to about 90 kilohms, from about 10 ohms to about 90 kilohangs, k < / RTI > From about 10 ohms to about 700 ohms, from about 10 ohms to about 500 ohms, from about 10 ohms to about 30 ohms, from about 10 ohms to about 20 kilohms, from about 10 ohms to about 10 kilohms, from about 10 ohms to about 1 kilohms, , From about 10 [Omega] to about 300 [Omega], or from about 10 [Omega] to about 100 [Omega]. The charge transfer resistance is closely related to the electrical conductivity of the hollow composite, and the lower the charge transfer resistance, the better the electrical conductivity of the hollow composite. The high electrical conductivity (low charge transfer resistance) of the hollow composite may be because the hollow composite comprises the carbon structure.

In one embodiment of the present invention, the hollow composite may include the carbon structure to further enhance the weak electrical conductivity of the metal oxide. Accordingly, the improved electrical conductivity of the hollow composite improves the performance of the electronic ink comprising the hollow composite and the electronic paper and display device comprising the electronic ink.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are given for the purpose of helping understanding of the present invention, but the present invention is not limited to the following Examples.

[Example]

1. rGO / TiO ₂  Manufacture of hollow nanospheres

(1) Synthesis of PS microspheres

Monodispersed polyvinylpyrrolidone (PVP) -modified polystyrene (PS) microspheres are used as the monomer, styrene as the initiator, 2,2'-azobisisobutyronitrile (2,2 ' -azobisisobutyronitrile, AIBN), and PVP as a stabilizing agent. Ideally, PVP (4 g) was dissolved in ethanol (55 mL) and purged under an Ar flow for 30 min prior to addition of styrene monomer (6.4 mL) and AIBN (1 wt%) previously dissolved in ethanol. After polymerization at 70 占 폚 for 24 hours, monodispersed PS microspheres with an average diameter of 1 占 퐉 were obtained. The PS microspheres formed were washed three times in succession with ethanol before re-dispersion (15 wt% solution) in ethanol and centrifuged.

(2) Synthesis of graphene oxide (GO)

The GO was fabricated by the modified Hummer method. Briefly, a graphite powder (1 g) was added to _{70 mL H 2 SO 4 (98} %). KMnO ₄ (3 g) and NaNO ₃ (0.5 g) that was then gradually added in an ice bath. The mixture was stirred for 4 hours, after which deionized water (100 mL) was added to the mixture. The formulations prepared by the process were maintained at this temperature for 30 minutes. H ₂ O ₂ solution (30%) was gradually added into the solution while stirring until the suspension turned to a light brown indicating complete oxidation of the graphite. The mixture was washed repeatedly with 5% HCl and deionized water and collected by centrifugation. The obtained graphite oxide powder was added to ethanol, and was peeled off by ultrasonication for 6 hours. The resulting suspension was centrifuged at 3000 rpm for 30 minutes, and the precipitates were removed and used to obtain a stable GO-ethanol suspension. The GO-ethanol suspension was further centrifuged at high rpm to separate the separated GO nanosheets.

(3) rGO / TiO ₂  Manufacture of hollow nanospheres

A rGO / TiO ₂ precursor solution was prepared according to the following procedure. Suspended GO in 7.6 mL ethanol containing 0.2 mL of HCl (37%) was sonicated for 2 hours. After the addition of 3.4 mL of titanium butoxide (TBOT), the solution was stirred at room temperature for 24 hours. The GO content was adjusted to obtain GO wt% of 5%, 10%, and 20% in the obtained GO / TiO ₂ precursor solution. TiO ₂ was initially nucleated and appeared to react with the available functional groups of the GO, which formed a 3D interconnected GO / TiO ₂ network.

The coated PS nanospheres (PS @ TiO _2), PS colloid (1 mL) the precursor solution the mixture prepared above and the (350 μL) is GO / TiO ₂ and PS interaction between the nanospheres in the preparation of - GO / TiO ₂ Lt; / RTI > for 30 minutes. Initial experiments were performed with a clear and reproducible PS @ GO / TiO ₂ Showed the effect of the ratio of GO / TiO ₂ precursor solution to colloidal PS nanospheres to obtain a complex. The ratios applied here were optimized from the initial experiments. Each prepared suspension (200 μL) was drop-cast onto a quartz substrate (2.5 x 8 cm ² ) and dried at room temperature. During the drying process, the TiO ₂ precursor was exposed to moisture in the air and hydrolysed with a metal oxide sol, which then formed a uniform, dense thin coating around each polystyrene bead Respectively. A two-step calcination process was considered in the synthesis of all rGO / TiO ₂ hybrids. The samples were first carbonized under an Ar flow of 500 캜 to secure the stability of the formed hollow structure and to efficiently remove the PS core. The temperature was then increased to 800 ° C to achieve complete crystallization of TiO _{2 in} the rGO / TiO ₂ hybrid structure. The corresponding synthesized material was subsequently expressed as rGO (5%) / TiO ₂ , rGO (10%) / TiO ₂ and rGO (20%) / TiO ₂ , depending on the selected GO wt% used in the precursor solution. The prepared rGO / TiO ₂ was evaluated with a TiO ₂ hollow nanosphere synthesized as a reference.

2. Characterization

(1) Characteristic analysis method

Surface morphology was characterized using scanning electron microscopy (SEM; JEOL JSM6700-F) and transmission electron microscopy (TEM; JEOL JSM-2100F operating at 200 kV). Synchrotron XRD was obtained by synchrotron X-ray diffraction (SXRD) at the beamline 17-BM in the Advanced Photon Source (APS) of the Argonne National Laboratory (ANL) . Samples were attached to Kapton ^® tapes and measured in transmission mode. A PerkinElmer ^® amorphous silicon (amorphous silicon) flat panel detector (flat panel detector) was used to collect two-dimensional XRD data. Integration of conventional intensity plot versus 2-theta 2D data was performed with the program GSAS (II). The wavelength used was 0.72768 Å. Raman spectra were recorded by T64000 (HORIABA Jobin Yvon, France). The X-ray photoelectron spectroscopy (XPS) spectra were measured by a Thermo Scientific K-Alpha XPS and were used for dual beam source and very low energy electron beam (ultra-low energy electron beam). Near-edge X-ray absorption near-edge spectroscopy (XANES) was performed in transmission mode in the beamline 9-BM of the APS, ANL. Data reduction and data analysis were performed with Athena software packages. The pre-edge was linearly fitted and removed. The post-edge background was determined using a cubic-spline-fit process and then removed. Normalization was performed by comparing the data with the height of the absorption edge at 50 eV. A monochromator was detuned to a maximum intensity of 80% at the Ti K edge to minimize the presence of higher harmonics. The X-ray beam was calibrated using a Ti metal foil K edge at 4966 eV.

(2) Switching between SCE calibration and RHE

The correction of the SCE reference electrode is described in the prior art [Y. Li, W. Zhou, H. Wang, L. Xie, Y. Liang, F. Wei, J.-C. Idrobo, SJ Pennycook, H. Dai, Nat Nano, 2012 , 7 , 394.). A standard three-electrode system was employed in Pt / C-deposited glass carbon electrodes, polished Pt wires were employed as working and counter electrodes, respectively, and SCE was employed as the reference electrode. The electrolyte was pre-purged and saturated with high purity H ₂ . Thereafter, at a scan rate of 0.1 mV / s, the current crossed zero is taken as the thermodynamic potential (SCE reference) for the hydrogen electrode reaction, at a potential obtained from a linear scanning voltammetry It worked. The zero current point was observed at -0.998 V, thus E _(RHE) = E _{(SCE) +} 0.998 V.

(3) Electrochemical measurement

For the electrochemical measurement, 5 mg of the above catalyst mixed with 50 μL of nafion was added dropwise to isopropanol (500 μL) using an ultrasonic wave for 1 hour. Then, 3 μL of ink was dispersed in a 3 mm rotating glass carbon electrode and dried in air. Electrochemical linear sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements were performed using a computer-controlled potentiostat in a 3-electrode glass electrochemical cell. The catalyst-loaded glass carbon electrode was used as a working electrode, Pt wire as a counter electrode, and a saturated calomel electrode (SCE, calibrated and converted to RHE) as a reference electrode. Prior to each measurement, a KOH electrolyte (0.1 M) was bubbled with N ₂ or O ₂ for 20 minutes and a continuous O ₂ flow was maintained during the measurement to ensure continuous O ₂ saturation. The potential range was cathodically scanned between 0.05 V and 1.05 V for RHE at a scan rate of 5 mV / s. The samples were compared with the commercial 20 wt% Pt / carbon black (Pt / C, Alpha Aeser) previously prepared.

3. Results and Analysis

(One) Morphology

The manufacturing process and the method of the hollow rGO-TiO ₂ hybrid (hybrid) applied in the embodiment are shown in FIGS. 1A and 1B. Functionalized PS nanospheres were strategically coated with GO / TiO ₂ in the GO / TiO ₂ precursor solution. The resultant core / shell composite was drop-cast on a quartz substrate and calcined at 500 ° C under Ar and then up to 800 ° C under air flow to form hollow rGO / TiO ₂ Nano spheres were obtained.

Representative SEM images were collected to evaluate the size and shape of the material synthesized in this embodiment. The prepared hybrid material synthesized using 10 wt% GO was compared with TiO ₂ - based hollow nanospheres as a comparative example. SEM images were first collected to confirm the synthesis of monodispersed PS nanospheres with a smooth surface and a uniform particle size of about 1 μm (FIG. 2a). SEM images of PS @ GO / TiO ₂ composite (FIG. 2b) and PS @ TiO ₂ (FIG. 3a) nanospheres having a core / shell structure were prepared by uniform coating of TiO ₂ and GO / TiO ₂ on a PS template, . The efficient synthesis of the core / shell composite structure resulted from strong electrostatic interactions between the carbonyl groups on the PS surface and the hydroxyl groups of TiO ₂ and GO. The deposition of TiO ₂ and GO / TiO ₂ is carried out so that the average diameter of the obtained material can be increased to about 1.1 μm and 1.24 μm in PS @ TiO ₂ and PS @ GO (10%) / TiO ₂ , respectively Respectively. Interestingly, an increase in PS @ GO / TiO ₂ mean diameter was suggested by increasing the GO concentration in the precursor solution. 3 shows a FESEM image of (a) PS @ TiO2, (b) rGO (5%) / TiO2, and (c) rGO (20%) / TiO2 hollow composite, and (d) rGO / TiO2 hollow composite (Scale bar is 1 [mu] m). This observation has been experimentally derived in the presence of the GO ' s abundant functional group, which appears to enhance the interaction with the PS carbonyl group. SEM images of uniform TiO ₂ and rGO (10%) / TiO ₂ hollow shells demonstrated efficient removal of PS in subsequent carbonization (FIGS. 2c and 2d). Although spherical morphology can be maintained in both cases, size shrinkage of about 10% to 15% has been demonstrated compared to the case without calcination. This observation has been attributed to the condensation / polymerization of the template associated with the sintering contraction of the TiO ₂ framework during the high temperature crystallization reaction. 4 is a TEM image showing (a) TiO2 (air), (b) TiO2, (c) rGO (20%) / TiO2 hollow and (d) HRTEM image of rGO (20%) / TiO2. The close inspection of the collected SEM and HRTEM images showed the presence of agglomerated TiO ₂ nanoparticles in TiO ₂ hollow nanospheres (FIG. 2c).

Representative TEM images of both TiO ₂ and rGO (10%) / TiO ₂ hollow spheres were collected in the subsequent two-step carbonization process. Figures 5A and 5C show a clear TEM image of TiO ₂ and rGO (10%) / TiO ₂ composite hollow spheres each having a diameter of about 800 nm. While the TiO ₂ hollow sphere is formed by randomly dispersed TiO ₂ nanoparticles having a size in the range of 10 nm to 50 nm, the thickness of the rGO (10%) / TiO ₂ and the continuous shell are on the rGO sheet Uniform coating of TiO ₂ nanoparticles with an average size of 10 nm. It was assumed that the abundant functional groups of rGO in this example were to reduce the particle size and agglomeration of the TiO ₂ nanoparticles in the rGO (10%) / TiO ₂ sample of the present application. Interestingly, a high-resolution TEM photograph showed the presence of a carbon coating-layer between 2 nm and 3 nm in thickness on each TiO ₂ nanoparticle in all evaluation samples (FIGS. 5B and 5D). The formed layer was presumed to be carbonaceous and was presumed to be the result of carbonization of the carbonyl groups in the modified PS nanosphere. The above estimates were in accordance with the recent literature reporting carbon coatings of TiO ₂ nanoparticles. The porous structure of all the samples was evaluated by N ₂ sorption measurement, and the results are shown in FIG. The strong uptake of N ₂ at high relative pressures proved the presence of a large macropore in the hollow structure. Most importantly, the N ₂ assessment in all rGO / TiO ₂ composites indicated a type-isotherm with a distinct H2-type hysteresis loop, a characteristic of the mesoporous material . The observation results were attributed to the presence of intraparticle voids as a result of agglomeration of crystalline nanoparticles having an average size of 10 nm in this example.

(2) Analysis of structure and chemical characteristics

The crystallographic phases of TiO ₂ and rGO / TiO ₂ hollow nanospheres were evaluated by synchrotron X-ray diffraction (SXRD) (FIG. 7A). It has been found that the SXRD pattern identified in all structures is consistent with both TiO ₂ anatase and rutile crystallographic phases (JCPDS No. 21-1272 and No. 21-1276, respectively). It was found that the variation of the ratio of anatase to ruta was negligible in mixing various rGO contents with TiO ₂ . The characteristic rGO diffraction peak was not found in the rGO / TiO- ₂ hybrid as a result of the latter being estimated as the weak diffraction intensity. Raman spectra were collected to investigate the binding properties of rGO and TiO ₂ in the hybrid structure (Fig. 7B). The band located at 155 (E _g ) and 398 cm ^-1 (B _1g ) were found to match the TiO ₂ anatase-crystal phase, whereas 250 (A _{1 g} ), 440 (E _g ), and 612 cm ^-1 (A _1g ) was found to be consistent with the TiO ₂ rutile. The results further reflected the presence of mixed TiO ₂ anatase and rutile crystalline phases as evidenced by XRD data. The mixed TiO ₂ crystal phases showed excellent catalytic activity because their conduction band differences appeared to inhibit the recombination of charge carriers. Interestingly, the E _g Raman mode of the strongest anatase at 155 cm ^-1 in rGO / TiO ₂ shifted by 8 cm ^-1 compared to the comparative TiO ₂ sample. Similar results were observed at an E _g peak of 440 cm ^-1 . The observed blue-shift was believed as a result of the Ti ^{3 +} induced oxygen defects (oxygen vacancy) or disorder (disorder). The bands at 1350 cm ^-1 and 1604 cm ^{-1 corresponded} to the D peak of disordered sp ² carbon and the G peak of the ordered graphite structure of graphene, respectively (FIG. 7d). These two bands were further observed in TiO ₂ hollow nanospheres, which characterize the carbon-coated layer covering the surface of the TiO ₂ nanoparticles upon carbonization at 500 ° C. (Fig. 5b). For comparison, TiO ₂ -based hollow nanospheres were calcined directly at 800 ° C atmospheric air (TiO ₂ (air) in Figure 5b). By characterization, the results confirmed the absence of both the D and G bands in the sample, suggesting complete elimination of species C during the calcination process.

High-resolution X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate the chemical states and effective integration of rGO and TiO ₂ (FIG. 8). The peaks at 282 eV to 292 eV, 526 eV to 536 eV, and 455 eV to 468 eV regions corresponded to C 1s (FIG. 8 e), O 1s (FIG. 8 c), and Ti 2p (FIG. After removing the spectral background by the Shirley method, the collected spectra were simply deconvoluted with the expected component peaks. rGO (10%) / ₂ TiO- hollow nanospheres is 459.1 eV and 464.8 eV in eotneunde indicate the Ti2p signal, this ² each Ti 2p ^3/2, and Ti 2p ^{1 /} Ti in the ⁴⁺ state spin-orbital splitting ( splitting) photoelectrons. Compared with the calcined Comparative TiO ₂ sample under air up to 800 ° C, it was clear that both signals slightly shifted from the corresponding peak of 458.1 eV and 464.1 eV to the higher energy region. The binding energy shift to the higher energy region was attributed to the transfer of electron density from Ti to rGO in the rGO / TiO ₂ composites produced (MSA Sher Shah, AR Park, K. Zhang, JH Park, PJ Yoo, ACS Appl . Mater. Interfaces 2012 , 4 , 3893). rGO / TiO ₂ is eotneunde indicate the two small type shoulder (shoulder-like) peak (Fig. 8b) at 457.4 eV and 463.2 eV, which was due to a defect of the Ti ^{3 +.} The Ti ^{3 +} species in surface or bulk TiO ₂ are known to be unstable and are therefore easily oxidized during the calcination process, which represents a clear challenge to obtain stable Ti ^{3 +} -doped TiO ₂ . However, in the present embodiment, it is believed that the species can be stabilized by TiO ₂ hybridization with rGO. The presence of Ti ^{3 +} species was observed to a lesser extent in the case of calcined TiO ₂ -based hollow nanospheres under Ar. This observation was due to the presence of the carbon layer formed on the TiO ₂ nanocrystals observed in the collected TEM image (Figure 5b). The presence of the carbon layer, even at a high temperature level, and was presumed to stabilize the doped Ti ^{+ 3} species, and surface oxygen deficiency in the crystal lattice. The above assumption was verified by comparing the Ti ^{3 +} peak characteristics observed in the comparative TiO ₂ reference to those not observed. In the absence of a carbon layer at 800 캜, Ti ^{3 +} was expected to be easily oxidized completely. The above results suggest that the generation and stabilization of O-Ti ^{3 +} species in TiO ₂ and rGO / TiO ₂ will be closely related to both the carbon coating and the rGO layer.

TiO ₂ and _{rGO (10%) / TiO 2} O1s XPS spectrum of the hollow nanospheres is 529.4 eV and eotneunde indicate a peak at 531.5 eV, which lattice oxygen in the TiO ₂ (TiO), respectively, and a surface hydroxyl group (Ti -OH) or OC = O (Figures 8c and 8d). At 532.3 eV, the shoulder peak demonstrated HO-C or carboxyl species in the presence of carbon and rGO. The peak of 530.3 eV was available for the O-Ti ^{3 +} in the two samples, and this is demonstrated by the Ti XPS data for the previous acquisition, and showed the Ti ^{+ 3} species content notable in rGO / TiO _2. The C1s XPS spectrum showed high intensity deconvoluted peaks at 284.4 eV centers corresponding to CC, C = C, and CH bonds (Figs. 8e and 8f). The peak at 284.4 eV corresponded to sp ² C = C of rGO in the evaluated rGO / TiO ₂ hollow nanospheres and was attributed to C = C formed in the graphite-on-carbon layer of TiO ₂ nanoparticles according to previous evidence . The oxygen-containing carbonaceous bonds were deconvoluted at higher binding energy levels corresponding to the C-OH, C = O, and -COOH groups, respectively, 285.3 eV, 286.7 eV, and 287.7 eV, O1s XPS data.

The Ti and Ti valences of the synthesized samples were further evaluated by X-ray absorption near-edge structure (XANES) spectroscopy (FIG. 9). The pre-edge characteristics generally generate three peaks labeled A1, A2, and A3, which represent the direct environment of a particular ion. In particular, the relative intensity of the A2 peak, the sensitivity of the Ti site structure reflects the local atomic arrangement around the titanium ion. In this example, it was found that the overall spectral characteristics of the synthesized sample were somewhat similar to those of anatase-type TiO ₂ , which proved the results of prior observations. The most interesting thing is that, the relative intensity of the A2 that was slightly increased as compared with Comparative Example TiO ₂ reference (Fig. 9b). This change was even more noticeable in the rGO (10%) / TiO ₂ hollow nanospheres of this example, indicating increased modification of the Ti coordination sphere as a result of carbon and rGO addition. The results suggest a Ti species of hollow nanospheres fabricated at a lower average oxidation state, which proved the XPS data.

(3) Conductivity

Electrochemical impedance spectroscopy (EIS) was performed at an open circuit potential in the frequency range of 10 ^-2 Hz to 10 ⁵ Hz to examine the electrical conductivity of the samples prepared above. The Nyquist plot of all evaluated samples is shown in Figure 10a. The diameter of the Nyquist plot in the high frequency region was related to the charge transfer resistance (R _ct ) of the evaluated electrode, while the smaller radius meant more efficient charge transfer. The calculated R _ct values are TiO ₂ (114.2 k)> rGO (5%) / TiO ₂ (48.5 k)> rGO (20%) / TiO ₂ (29.9 k)> rGO (10%) / TiO ₂ (16.8 k). These results reflected the influence of the introduced rGO layer which allowed for easier electron transfer, which was presumed to have a significant effect on the ORR activity of the catalyst obtained. The somewhat higher charge transfer resistance achieved in rGO (20%) / TiO ₂ could be attributed to the thicker nature of the shell as evidenced by the corresponding SEM image.

In order to reveal the effect on the conductivity of the evaluated samples of the proven thin carbon layer formation in TEM, the results were compared with the calcined Comparative TiO ₂ reference under 800 ° C air flow as described above. The reference sample exhibited a significantly higher resistance value (182.4 k), indicating a weak inherent electrical conductivity of the individual TiO ₂ nanoparticles. The above results further reflect that there is little application of TiO ₂ as a single ORR electrocatalyst, thus indicating the novelty of the present invention. Most importantly, it is concluded that the cooperative effect of both the rGO and the formed carbon layer is a notable 11-fold improvement in TiO ₂ conductivity in the best sample (rGO (10%) / TiO ₂ ) of this example Down.

Mott-Schottky measurements were additionally performed on all rGO / TiO ₂ and TiO ₂ -based hollow nanospheres at a frequency of 5 kHz to further investigate the effect of self-doping and rGO mixed TiO ₂ ( 10b). Consistent with the above results, calcined TiO ₂ samples in the atmosphere were additionally evaluated to investigate the effect of the carbon layer formed by carbonization. All samples showed the same positive slope as the n-type semiconductor material as expected (Fig. 10B). The values were calculated from the slope of the Mott-Schottky plot according to Equation 1 below:

<Formula 1>

e ₀ is the dielectric constant of TiO ₂ determined based on the ratio of the TiO ₂ crystal phase composition (XRD), ε ₀ is the permittivity of vacuum, N _d is the donor density , And V is the bias applied at the electrode. The calculated electron density is rGO (10%) / TiO ₂ (3.5 x 10 ²¹ )> rGO (5%) / TiO ₂ (2.7 x 10 ²¹ )> rGO (20%) / TiO ₂ (9.3 x 10 ²⁰ ) TiO ₂ (2.1 x 10 ²⁰ )> TiO ₂ (air) (6.2 x 10 ¹⁹ ). In particular, the presence of a thin carbon layer in TiO ₂ nanoparticles has been shown to play an important role here in significantly increasing donor density. The increased donor density was consistent with XPS data demonstrating an increase in oxygen deficiency known as an electron donor in Ti ^{3 +} doping and TiO ₂ . The increased charge-carrier density produced the above-described improved electrical conductivity and better electron charge separation within the electrode.

(4) Electrocatalytic  Performance

Electrocatalytic measurements were performed as described in 2. Characterization. The prepared sample was conveniently compared with the conventional catalyst Pt / C as a reference (comparative example). The ORR electrocatalytic activity of all the samples was initially assessed by loading the active material onto a free carbon electrode using cyclic voltammetry (CV), which was characterized by the O ₂ saturated Was performed in a potential window of 0 V to 1.2 V at a constant scan rate of 20 mV / s in 0.1 M KOH aqueous solution (FIG. 11A). The CV of the TiO ₂ and rGO / TiO ₂ hollow nanospheres showed a unique cathodic ORR peak around 0.7 V RHE, suggesting a distinct electrocatalytic activity of the novel material in the ORR. No characteristic CV curves were observed within the above evaluated range in N ₂ -saturated solution (FIG. 12).

The ORR activity of all the samples was further investigated in a rotating disk electrode (RDE) measurement. A linear sweep voltammogram (LSV), recorded in the range of 400 rpm to 2500 rpm rotational speed, demonstrated an improvement in current density with increasing rotation, which resulted in higher availability of oxygen diffused from the electrode surface, (Fig. 11C). Thus, at lower values, the ORR curve showed mass transfer limitation due to diffusion of oxygen dissolved in KOH aqueous solution.

The LSV curve in all manufactured samples was analyzed at a fixed rotational speed of 1,600 rpm and compared with commercial Pt / C (FIG. 11B). Based on the influence of the presence of a thin carbon layer on the improved conductivity of the TiO ₂ sample, the results were compared with the calcined Comparative TiO ₂ -reference in the atmosphere. The catalyst parameters are summarized in Table 1 below.

<Table 1>

RGO (10%) / TiO ₂ and rGO (20%) / TiO ₂ showed oxygen reduction at similar onset potential values (0.82 V), whereas Pt / C showed a value of 1.01 V. As expected, the rGO / TiO ₂ sample exhibited an excellent onset potential compared to the value (0.70 V) achieved in the calcined Comparative TiO ₂ - reference in the atmosphere. Similarly, the ORR half-wave potential of the rGO / TiO ₂ sample described above, where the magnitude of the current is defined as the potential (0.70 V in this case) which is one-half of the limiting current, is compared with the TiO ₂ reference (0.54 V) Lt; / RTI &gt; In each case, the results emphasize good ORR electrocatalytic activity as suggested by comparison with Pt / C samples (0.82 V). Under the operating conditions described above, the current density at 0.1 V RHE is increased by 5%, 10%, and 20%, respectively, compared to the value achieved by Pt / C (-5.4 mA / cm ² ) , It can be increased stably to -4.5 mA / cm ² , -5.0 mA / cm ² , and -5.5 mA / cm ² (Table 1). The above results underscore the effect of hybridization of TiO ₂ with rGO to enhance the ORR performance of the original TiO ₂ material.

The improved ORR activity could be attributed to accelerated charge transfer across the interface depending on the difference in Fermi level. The presence of the Ti ^{3 +} region was further believed to increase the electron density and shift the Fermi level of TiO ₂ towards the conduction band. The upward shift of the Fermi level facilitated charge separation at the electrode / electrolyte interface. The formation of a thin carbon layer on the formed TiO ₂ nanoparticles was further demonstrated to play an important role in the methodology (Table 1). The resultant carbon-coated layer showed an improvement in the electrocatalytic properties of TiO ₂ and enabled the presence of higher conductivity levels, oxygen defects and reduced Ti ^{3 +} , and a contact resistance between the active material particles ).

The kinetic analysis was performed using Koutecky-Levich (KL) equation (2) to determine the electron transfer number (n) and the kinetic current density (i _k )

<Formula 2>

i is the measured current, i _k is the dynamic current, and? is the electrode rotation speed. KL plots were obtained from currents using different rotational speeds at different potentials (Figure 13). The number of electrons transferred in the ORR, n, was calculated from the slope of the line at different potentials according to Equation 3 below:

<Formula 3>

n is the number of electron transfer oxygen per molecule, F is the Faraday constant ^{(96,485 C mol -1), C} O2 is the oxygen concentration of 0.1 M KOH in saturated aqueous solution ^{(1.2 x 10 - 6 mol cm} -3), D O2 is Oxygen diffusion coefficient (1.73 x 10 ^-5 cm ² s ^-1 ), and v is the kinematic viscosity of the solution (0.01 cm ² s ^-1 ). The number of transferred electrons (n) calculated from the slope of the KL plot at RHE bases 0 V to 0.5 V indicated a two-electron reaction pathway from O ₂ to hydrogen peroxide.

For better comparison of rGO / TiO ₂ hybrid electrocatalysts, the ORR activity was further investigated according to the Tafel slope of low overvoltage in O ₂ -saturated 0.1 M KOH aqueous solution (FIG. 11 d). The E versus log (- i ) curves in the 0.80 V to 0.85 V range showed somewhat similar changes in the reaction mechanism with potentials. rGO (10%) / TiO ₂ has a smaller Tafel slope compared to rGO (5%) / TiO ₂ (114 mV / dec) and rGO (20%) / TiO ₂ (73 mV / dec) (66 mV / dec). Based on the CV and RDE measurements, the rGO / TiO ₂ sample exhibited a very good ORR catalytic activity with a greater positive ORR onset potential and a larger positive half-wave potential than TiO ₂ , _{2 &lt}; / RTI &gt; catalyst activity. The evaluation of the effect of rGO concentration in the prepared samples showed a higher ORR electrocatalytic activity of rGO (10%) / TiO ₂ in all samples.

To evaluate the effect of electrochemically accessible surface area enhancement, rGO (10%) / TiO ₂ hybrids were additionally prepared under the same synthesis conditions without the use of PS templates. The resulting rGO (10%) / TiO ₂ structure exhibited significantly lower electrocatalytic activity as compared to the corresponding hollow nanospheres, which clearly demonstrated the effect of the morphology of these materials on ORR activity. Thus, except for the formed carbon-coated layer, Ti ^{3 +} -doped and rGO hybrid, the larger contact area between the electrode and the electrolyte (KOH), and the greater number of active sites contribute to higher ORR activity .

To assess the applicability of the samples described herein, durability and methanol tolerance were further assessed. The durability of the rGO / TiO ₂ hollow nanospheres was measured at 1,600 rpm in KOH (0.1 M) saturated with O ₂ for 20,000 seconds at 0.5 V RHE. Higher relative current values were measured in the novel rGO / TiO ₂ hybrid samples of the present invention, which emphasized excellent stability compared to conventional Pt / C samples (FIG. 14A). The unique design of the novel materials herein as hollow nanospheres was believed to play a significant role in increasing the durability of rGO / TiO ₂ , which provides a higher contact area between the electrode and the electrolyte and more active sites in the ORR . The rGO / TiO ₂ hollow nanospheres were additionally tested for methanol crossover via chronoamperometric response under the operating conditions described above (FIG. 14b). With the addition of methanol (3 wt.%) Into the electrolyte solution, the Pt / C catalyst exhibited a drastic reduction in performance, highlighting one of the major drawbacks in the long cycle performance of Pt / C as a conventional ORR catalyst . On the other hand, rGO (5%) and rGO (10%) / TiO ₂ hollow nanospheres showed stable amperometric response. The outstanding methanol tolerance highlighted herein was to further emphasize the promising applicability of the hollow nanospheres and in particular the rGO (5%) / TiO ₂ sample, which is the best here. However, the above proposed results achieved in rGO (20%) / TiO ₂ were expected to result in lower methanol tolerance with successive increases in rGO content.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (25)

As the hollow composite,
Wherein the hollow composite comprises a shell comprising a hybrid comprising a metal oxide and a carbon structure,
Wherein the hybrid is self-doped by a metal element contained in the metal oxide,
Wherein the inner surface of the shell of the hollow composite comprises carbon,
The metal oxide and the carbon structure of the hybrid are hybridized,
The carbon structure may be selected from the group consisting of reduced graphene oxide (rGO), graphene, graphite, single wall carbon nanotubes, multiwall carbon nanotubes, carbon nanohorns, vapor- grown carbon fibers and carbon nanofibers, synthetic carbon sources, and combinations thereof. &lt; RTI ID = 0.0 &gt;
Hollow composite.
The method according to claim 1,
Wherein the metal oxide comprises a semiconductor oxide.
3. The method of claim 2,
The semiconductor oxide is made of a _{TiO 2, SnO 2, ZnO,} VO 2, In 2 O 3, NiO, MoO 3, SrTiO 3, Fe- doped _{SrTiO 3, Fe 2 O 3,} WO 3, CuO, and BiVO ₄ &Lt; / RTI &gt; and at least one semiconductor oxide selected from the group consisting of silicon oxides.
delete The method according to claim 1,
Wherein the metal element is in a state more reduced than the metal cation contained in the metal oxide.
The method according to claim 1,
Wherein the size of the hollow composite is in the range of 50 nm to 5,000 nm.
The method according to claim 1,
Wherein the carbon structure content is from 1 part by weight to 20 parts by weight based on 100 parts by weight of the hollow composite.
The method according to claim 1,
Wherein the hollow composite has a charge transfer resistance of 10 OMEGA to 200 k [Omega].
Coating a polymer core with a mixed solution containing a precursor for a metal oxide and a precursor for a carbon structure to form a core-shell composite in which the precursor is coated on the polymer core particle; and
First calcining the core-shell composite to obtain a hollow composite
/ RTI &gt;
Wherein the shell of the hollow composite comprises a hybrid comprising a metal oxide and a carbon structure,
The hybrid is self-doped by a metal element contained in the metal oxide,
The first calcination may be carried out,
Heating the core-shell composite at a first temperature to carbonize and remove the polymer core particles to obtain the hollow composite.
/ RTI &gt;
10. The method of claim 9,
By the first calcination,
Wherein the polymer core particles of the core-shell composite are carbonized and removed and the inner surface of the shell of the hollow composite is formed by the carbonization of the surface functional groups of the polymer core particles in contact with the inner surface of the shell of the core- Carbon, wherein at least a portion of the metal cations of the metal oxide are reduced to form the metal element self-doping the hybrid.
/ RTI &gt;
10. The method of claim 9,
Heating the hollow composite obtained in the first calcination at a second temperature higher than the first temperature to crystallize the metal oxide contained in the hybrid. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI & Way.
10. The method of claim 9,
Wherein the metal oxide comprises a semiconductor oxide.
13. The method of claim 12,
The semiconductor oxide is made of a _{TiO 2, SnO 2, ZnO,} VO 2, In 2 O 3, NiO, MoO 3, SrTiO 3, Fe- doped _{SrTiO 3, Fe 2 O 3,} WO 3, CuO, and BiVO ₄ Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; and one or more semiconductor oxides selected from the group.
10. The method of claim 9,
The carbon structure may be selected from the group consisting of reduced graphene oxide (rGO), graphene, graphite, single wall carbon nanotubes, multiwall carbon nanotubes, carbon nanohorns, vapor- grown carbon fibers and carbon nanofibers, synthetic carbon sources, and combinations thereof. &lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
10. The method of claim 9,
Wherein the size of the hollow composite is in the range of 50 nm to 5,000 nm.
10. The method of claim 9,
Wherein the content of the carbon structure is from 1 part by weight to 20 parts by weight based on 100 parts by weight of the hollow composite.
An electrocatalyst comprising a hollow composite according to any one of claims 1 to 3 and 5 to 8.
18. The method of claim 17,
Wherein the electrocatalyst is for an oxygen reduction reaction.
An electrode, comprising a hollow composite according to any one of claims 1 to 3 and 5 to 8.
20. The method of claim 19,
Wherein the electrode is for an oxygen reduction reaction.
20. A battery comprising an electrode according to claim 19.
The battery according to claim 21, wherein the battery is a fuel cell or a secondary battery.
An electronic ink comprising a hollow composite according to any one of claims 1 to 3 and 5 to 8.
An electronic paper comprising the electronic ink according to claim 23.
25. A display device comprising electronic ink according to claim 23.

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