Effects of sodium content of titanate nanotubes on lithium battery performance.

Yoon, Yongsub,Shin, Dongwook,Kim, Donghyun,Lee, Kyungsub,Kim, Sunjae American Scientific Publishers 2010 Journal of nanoscience and nanotechnology Vol.10 No.9

<P>Titanate nanotubes were prepared by hydrothermal process of powder for the application to the anode of lithium batteries. After the synthesis of titanate nanotubes by the chemical treatment with 10 M NaOH solution, the quantity of sodium remnant was controlled by the HCl washing solutions of different pH of 1, 4, 7, 10 and 13. The prepared titanate nanotubes had outer and inner diameter of 9 nm and 6 nm, and the interlayer spacing of about 1 nm. The amount of sodium remnant was investigated using Inductively Coupled Plasma (ICP) Atomic Emission Spectrometer, and the variation of structure and morphology with the contents of the sodium was studied by X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), Field Emission Scanning Electron Microscopy (FE-SEM) and High Resolution Transmission Electron Microscopy (HR-TEM). Coin cells composed of (Titanate nanotubes//1 M LiPF6-EC/DEC//Li metal) were prepared for studying the basic charging-discharging behavior and electrochemical properties of the prepared titanate nanotubes with controlled sodium contents. The effects of the remnant sodium content on the microstructures, morphology and electrochemical properties of titanate nanotubes will be discussed.</P>

Yttria stabilized zirconia films deposited by electro-spray deposition for solid oxide fuel cells

Yongsub Yoon,임종모,신동욱 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.2

Solid oxide fuel cells(SOFCs) are interesting as an energy conversion system of the future with high efficiency and environmental cleanness. To fabricate the micro-fuel cell for mobile applications, it is essential to develop a process for the deposition of dense electrolyte films. In this study, for a micro-SOFC application, YSZ electrolyte films were prepared by an electro-spray deposition (ESD) method. The deposition parameters studied were deposition temperature, distance between nozzle and substrate, solution concentration and DC voltage. Depending on these parameters, the surfaces were remarkably changed from cracked or rough surfaces to smooth and dense films. Dense films was prepared with the conditions of a nozzlesubstrate distance of 4 cm, a deposition temperature of 150℃, a deposition time of 4 minutes, and a voltage of 16 kV. Solid oxide fuel cells(SOFCs) are interesting as an energy conversion system of the future with high efficiency and environmental cleanness. To fabricate the micro-fuel cell for mobile applications, it is essential to develop a process for the deposition of dense electrolyte films. In this study, for a micro-SOFC application, YSZ electrolyte films were prepared by an electro-spray deposition (ESD) method. The deposition parameters studied were deposition temperature, distance between nozzle and substrate, solution concentration and DC voltage. Depending on these parameters, the surfaces were remarkably changed from cracked or rough surfaces to smooth and dense films. Dense films was prepared with the conditions of a nozzlesubstrate distance of 4 cm, a deposition temperature of 150℃, a deposition time of 4 minutes, and a voltage of 16 kV.

Developing a Path Model of International Tourism Demand

Yooshik Yoon,Yongsub Kwock,Jongseo Yu 한국문화관광학회 2002 문화관광연구 Vol.4 No.2

The objective of this study was to develop an empirical path model for the international tourism demand. Through series regression analyses of time series data for 18 years, the determinants of tourism demand in a case of tourists’ flow from Canada to the USA were investigated. Six determinants (TPI, exchange rate, population, GDP, percentage of imports, and percentage of exports) and four demand measures (arrivals, receipts from Canada as intervening variables, total arrivals, and receipts from USA as dependent variables were employed to examine four different regression equations of the hypothesized model. The results indicated that the explained variances (R-square) of each model range from 99, 97, 90, and 92 (%) respectively (p < .001). TPI, exports, imports and exchange rate are identified as major determinants that have been generating tourism demand from Canada to the USA. Additionally, the results showed that arrivals and receipts from Canada have been affecting the total number of arrivals and receipts in the USA, meaning that Canada is one of the significant markets for the USA international tourism demand. Finally, this study suggested that the results of this study may help to efficiently develop and promote tourism policy and marketing programs for international tourism demand.

Electrochemical characteristics of tin oxide and tin/tin oxide composite powder synthesized by aerosol flame deposition

Dongwook Shin,Yongsub Yoon,신동욱 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.6

Gadolinia-Doped Ceria Films Prepared by Using an Air-Blast Spray Deposition Technique

신동욱,임종모,Yongsub Yoon 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

In this work, air-blast spray deposition (ASD) was applied to prepare dense gadolinia-doped ceria (GDC) films on silicon substrates for electrolyte applications in solid oxide fuel cells. The morphology of the GDC lm depended on process parameters such as the substrate temperature, the liquid flow rate, the deposition time and the nozzle-substrate distance. The effects of heating temperature on the crystal structures of the lms were investigated with X-ray diffraction (XRD) in the heating temperature range of 400 ℃ to 1000 ℃. A dense GDC film was successfully prepared in a solution ow rate range of 1 l/min to 1.8 l/min, a substrate temperature range of 149 ℃ to 243 ℃, a nozzle-substrate distance range of 1 cm to 6 cm and a deposition time range of 0.5 min to 4 min. In this work, air-blast spray deposition (ASD) was applied to prepare dense gadolinia-doped ceria (GDC) films on silicon substrates for electrolyte applications in solid oxide fuel cells. The morphology of the GDC lm depended on process parameters such as the substrate temperature, the liquid flow rate, the deposition time and the nozzle-substrate distance. The effects of heating temperature on the crystal structures of the lms were investigated with X-ray diffraction (XRD) in the heating temperature range of 400 ℃ to 1000 ℃. A dense GDC film was successfully prepared in a solution ow rate range of 1 l/min to 1.8 l/min, a substrate temperature range of 149 ℃ to 243 ℃, a nozzle-substrate distance range of 1 cm to 6 cm and a deposition time range of 0.5 min to 4 min.

Preparation of SnO2-B2O3-P2O5 for the anode of Li-ion batteries by aerosol flame deposition(AFD)

Jangwon Oh,Yongsub Yoon,신동욱 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.5

Targeted Base Editing via RNA-Guided Cytidine Deaminases in Xenopus laevis Embryos

Park, Dong-Seok,Yoon, Mijung,Kweon, Jiyeon,Jang, An-Hee,Kim, Yongsub,Choi, Sun-Cheol Korean Society for Molecular and Cellular Biology 2017 Molecules and cells Vol.40 No.11

Genome editing using programmable nucleases such as CRISPR/Cas9 or Cpf1 has emerged as powerful tools for gene knock-out or knock-in in various organisms. While most genetic diseases are caused by point mutations, these genome-editing approaches are inefficient in inducing single-nucleotide substitutions. Recently, Cas9-linked cytidine deaminases, named base editors (BEs), have been shown to convert cytidine to uridine efficiently, leading to targeted single-base pair substitutions in human cells and organisms. Here, we first report on the generation of Xenopus laevis mutants with targeted single-base pair substitutions using this RNA-guided programmable deaminase. Injection of base editor 3 (BE3) ribonucleoprotein targeting the tyrosinase (tyr) gene in early embryos can induce site-specific base conversions with the rates of up to 20.5%, resulting in oculocutaneous albinism phenotypes without off-target mutations. We further test this base-editing system by targeting the tp53 gene with the result that the expected single-base pair substitutions are observed at the target site. Collectively, these data establish that the programmable deaminases are efficient tools for creating targeted point mutations for human disease modeling in Xenopus.

Effect of interlayer spacing on the electrochemical properties of alkali titanate nanotubes.

Eom, Minyong,Kim, Junghoon,Yoon, Yongsub,Shin, Dongwook American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5

<P>Multilayered titanate nanotubes (TNTs) has been considered as a candidate for lithium ion battery anode material. However, it has a problem of high irreversible capacity due to trapped lithium ions in the interlayer space. To solve this problem, an attempt to enlarge the interlayer spacing has been made in this work to improve intercalation characteristics of TNTs. Monoatomic ions in hydrothermally heat-treated TNTs were substituted to one of Li, Na and K alkali ions via ion-exchange process. The TNTs (200) interlayer spacing peak in XRD patterns showed a shift to a lower angle, indicating an enlarged interlayer spacing of TNTs. The Li-, Na- and K-ion exchanged TNTs exhibited an initial capacity of 214, 230 and 248 mA h/g at 0.1 C, respectively, in the TNTs // LiPF6 electrolyte // Li metal coin type cell test. It was found that the enlarged interlayer spacing resulted in an increment in the specific capacity and rate capability. This increase was attributed to both the enhanced lithium ion diffusion and the increased number of lithium ion intercalation sites in the TNTs interlayers.</P>

Effect of the Valence States of Titanium on the Lattice Structure and Ionic Conductivity of Li0.33La0.55TiO3 Solid Electrolyte

Kyoungmin Kim,Jung-Hoon Kim,Yongsub Yoon,신동욱 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.1

Li0.33La0.55TiO3 solid electrolytes with a pure phase were synthesized by the citric acid-supported sol-gelmethod and then sintered under controlled redox atmospheres of air, argon and hydrogen. Although ofsimilar morphology and relative density, Li0.33La0.55TiO3 samples sintered under reduction atmosphere suchas argon and hydrogen exhibited a tetragonal structure with lattice distortion. The distortion and volumeexpansion of the crystal lattice was identified as originating from the transformation of the Ti valence state,and this was more clearly observed under sintering of the hydrogen atmosphere. The qualitative analysisof the Ti valence state using an X-ray Photoelectron Spectroscopy experiment was performed and indi-cated that the largest amount of Ti3+(18.6%) was formed in the Li0.33La0.55TiO3 samples sintered underhydrogen atmosphere. The relationship between the lattice distortion and the lithium ion conductivity of theLi0.33La0.55TiO3 sintered under different atmospheres is also discussed on the basis of the lattice distortion.