• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.375-375
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• 2012

Graphene is a sp2-hybridized carbon sheet with an atomic-level thickness and a wide range of graphene applications has been intensely investigated due to its unique electrical, optical, and mechanical properties. In particular, hybrid graphene structures combined with various nanomaterials have been studied in energy- and sensor-based applications due to the high conductivity, large surface area and enhanced reactivity of the nanostructures. Conventional metal-catalytic growth method, however, makes useful applications difficult since a transfer process, used to separate graphene from the metal substrate, should be required. Recently several papers have been published on direct graphene growth on the two dimensional planar substrates, but it is necessary to explore a direct growth of hierarchical nanostructures for the future graphene applications. In this study, uniform graphene layers were successfully synthesized on highly dense dielectric nanowires (NWs) without any external catalysts. We also demonstrated that the graphene morphology on NWs can be controlled by the growth parameters, such as temperature or partial pressure in chemical vapor deposition (CVD) system. This direct growth method can be readily applied to the fabrication of nanoscale graphene electrode with designed structures because a wide range of nanostructured template is available. In addition, we believe that the direct growth growth approach and morphological control of graphene are promising for the advanced graphene applications such as super capacitors or bio-sensors.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.244-260
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• 2018

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a $TiO_2$ photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured $TiO_2$ electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.400-405
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• 2016

Ferric oxide (${\alpha}-Fe_2O_3$, hematite) is an n-type semiconductor; due to its narrow band gap ($E_g=2.1eV$), it is a highly attractive and desirable material for use in solar hydrogenation by water oxidation. However, the actual conversion efficiency achieved with $Fe_2O_3$ is considerably lower than the theoretical values because the considerably short diffusion length (2-4 nm) of holes in $Fe_2O_3$ induces excessive charge recombination and low absorption. This is a significant hurdle that must be overcome in order to obtain high solar-to-hydrogen conversion efficiency. In consideration of this, it is thought that elemental doping, which may make it possible to enhance the charge transfer at the interface, will have a marked effect in terms of improving the photoactivities of ${\alpha}-Fe_2O_3$ photoanodes. Herein, we report on the synthesis by pulsed electrodeposition of ${\alpha}-Fe_2O_3$-based anodes; we also report on the resulting photoelectrochemical (PEC) properties. We attempted Ti-doping to enhance the PEC properties of ${\alpha}-Fe_2O_3$ anodes. It is revealed that the photocurrent density of a bare ${\alpha}-Fe_2O_3$ anode can be dramatically changed by controlling the condition of the electrodeposition and the concentration of $TiCl_3$. Under optimum conditions, a modified ${\alpha}-Fe_2O_3$ anode exhibits a maximum photocurrent density of $0.4mA/cm^2$ at 1.23 V vs. reversible hydrogen electrode (RHE) under 1.5 G simulated sunlight illumination; this photocurrent density value is about 3 times greater than that of unmodified ${\alpha}-Fe_2O_3$ anodes.

• Applied Chemistry for Engineering
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• v.18 no.2
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• pp.142-147
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• 2007

In this study, mesoporous tin oxide was synthesized by sol-gel method using $C_{16}TMABr$ surfactant as a template in a basic condition. The optimum conditions for the synthesis of mesoporous $SnO_2$ were investigated and the obtained samples were characterized by XRD, nitrogen adsorption and TEM analysis. A mesoporous and nanostructured $SnO_2$ gas sensor with Au electrode and Pt heater has been fabricated on alumina substrate as one unit via a screen printing process. Sensing abilities of fabricated sensors were examined for CO and $CH_4$ gases, respectively, at $350^{\circ}C$ in the concentration range of 1~10,000 ppm. Influence of loading amount of palladium impregnated on $SnO_2$ was also tested in detection of those gases. High sensitivity to detecting gases and the fast response speed with stability were obtained with the mesoporous tin oxide sensor as compared to a non-porous one under the same detection conditions.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.337-337
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• 2012

Dye sensitized solar cell (DSSC) having high efficiency with low cost was first reported by Gr$\ddot{a}$tzel et al. Many DSSC research groups attempt to enhance energy conversion efficiency by modifying the dye, electrolyte, Pt-coated electrode, and $TiO_2$ films. However, there are still some problems against realization of high-sensitivity DSSC such as the recombination of injected electrons in conduction band and the limited adsorption of dye on $TiO_2$ surface. The surface of $TiO_2$ is very important for improving hydrophilic property and dye adsorption on its surface. In this paper, we report a very efficient method to improve the efficiency and stability of DSSC with nano-structured $TiO_2$. Atmospheric plasma system was utilized for nitrogen plasma treatment on nano-structured $TiO_2$ film. We confirmed that the efficiency of DSSC was significantly dependent on plasma power. Relative in the $TiO_2$ surface change and characteristics after plasma was investigated by various analysis methods. The structure of $TiO_2$ films was examined by X-ray diffraction (XRD). The morphology of $TiO_2$ films was observed using a field emission scanning electron microscope (FE-SEM). The surface elemental composition was determined using X-ray photoelectron spectroscopy (XPS). Each of plasma power differently affected conversion efficiency of DSSC with plasma-treated $TiO_2$ compared to untreated DSSC under AM 1.5 G spectral illumination of $100mWcm^{-2}$.

• Applied Chemistry for Engineering
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• v.21 no.3
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• pp.291-294
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• 2010

Recently, the design of the multi-layered $TiO_2$ electrodes has been attracted for high efficiency of dye-sensitized solar cells. In this study, conversion efficiency of the multi-layered $TiO_2$ electrodes was investigated by using small and large $TiO_2$ nanoparticles. Nanostructured $TiO_2$ powders were prepared by $TiCl_4$ hydrolysis. Differently sized $TiO_2$ powders of which the average diameter was 7.6 and 18 nm were obtained by controlled calcination temperature. It was confirmed that multi-layered $TiO_2$ electrodes significantly influence short-circuit current (Jsc) and also show higher conversion efficiency than dye-sensitized solar cells consisting of each particles.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.846-850
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• 2011

Nanocomposite anodes for rechargeable lithium battery are prepared by mixing tin and nickel nanoparticles via wet method and their electrochemical properties are examined. The Sn-Ni nanocomposite anode shows a maximum discharge capacity of 700 mAh $g^{-1}$ at the first cycle but very poor cycle performance. This means that the electrode porosity and the Ni component formed by the simple mixing of nanoparticles no longer play the role of buffering the volume expansion/contraction of Sn component during charge-discharge. To solve the cycle performance problem, a novel nanostructured Sn-Ni anode should be designed and tested.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.342-347
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• 2011

We fabricated the silicon nanodots using the low pressure chemical vapor deposition technique to investigate their electron field emission characteristics. Atomic force microscope measurements performed for the silicon nanodot samples having various process parameters, such as, deposition time and deposition pressure, revealed that the silicon nanodots with an average size of 20 nm, height of 5 nm, and density of $1.3\;{\times}\;10^{11}\;cm^{-2}$ were easily formed. Electron field emission measurements were performed with the silicon nanodot layer as the cathode electrode. The current-voltage curves revealed that the threshold electric field was as low as $8.3\;V/{\mu}m$ and the field enhancement factor reached as large as 698, which is compatible with the silicon cathode tips fabricated by other techniques. These electron field emission results point to the possibility of using a silicon-based light source for display devices.

• Membrane Journal
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• v.31 no.6
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• pp.417-425
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• 2021

As the demand for high-capacity batteries increases, there has been growing researches on the lithium metal anode with a capacity (3,860 mAh/g) of higher than that of conventional one and a low electrochemical potential (-3.040 V). In this study, using the anatase phased TiO₂ nanoparticles synthesized by hydrothermal synthesis, a PVdF-HFP/TiO₂ organic/inorganic composite material was designed and used as an interfacial protective layer for a Li metal anode. As-formed organic/inorganic-lithium composite thin film was confirmed through the crystalline structure and morphological analyses. In addition, the electrochemical test (cycle stability and voltage profile) confirmed that the protective layer of PVdF-HFP/TiO₂ composite (10 wt% TiO₂ and 1.1 ㎛ film thickness) contributed to the enhanced electrochemical performance of the lithium metal anode (Colombic efficiency retention: 90% for 77 cycles). Based on comparative test with the untreated lithium electrode, it was confirmed that our protective layer plays an important role to stabilize/improve the EC performance of the lithium metal negative electrode.