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펄스전류파형을 이용한 Ti 전극위에서 BaTiO<sub>3</sub>박막의 합성
강진욱,탁용석,Kang, Jinwook,Tak, Yongsug 한국공업화학회 1998 공업화학 Vol.9 No.7
$85^{\circ}C$, 0.4 M $Ba(OH)_2$용액내에서 펄스전류파형을 이용하여 Ti전극위에 $BaTiO_3$박막을 전해 합성하였다. 환원전류 밀도 및 환원시간이 증가함에 따라 $BaTiO_3$의 결정성 및 페러데이 효율이 증가하였으며, 이는 표면 및 전기화학적특성 분석에 의하면 환원 전류 인가시에 $H_2O$의 환원에 의하여 전극표면의 pH가 증가함으로서 산화전류에 의하여 형성된 산화막의 구조변화가 빠르게 진행되기 때문으로 추측된다. 그리고 0.1M $H_2SO_4$용액하에서 산화막을 형성시킨 후 $BaTiO_3$형성에 미치는 영향을 분석한 결과, 산화막 두께가 증가함에 따라서 산화막을 통한 $Ti^{+4}$이온의 이동이 어려워지면서 $BaTiO_3$형성이 억제되며, 일정두께이상에서는 산화막 결함부위에서 결정이 형성됨을 알 수 있었다. $BaTiO_3$ thin film was electrochemically deposited on Ti electrode in a 0.4 M $Ba(OH)_2$ solution of $85^{\circ}C$ using a current pulse waveform. Both $BaTiO_3$ crystallinity and faradaic efficiency for the film formation were enhanced with the increase of cathodic current density and pulse time. Based on the surface analysis and electrochemical studies, it was suggested that, during cathodic pulsed, the surface pH increase due to the reduction of $H_2O$ accelerates the structural changes of Ti oxides which were formed during anodic cycle. Prior to experiments, Ti oxides were intentionally grown in 0.1 M $H_2SO_4$ solution and the effect of initial oxide film thickness on the $BaTiO_3$ film formation was investigated. The migration of $Ti^{+4}$ ions through the oxide film was retarded with the increase of film thickness and it was observed that the crystallization of $BaTiO_3$ was only limited to the defect area of surface oxides.
Lee, Gibaek,Choi, Hyeonji,Tak, Yongsug IOP 2019 Nanotechnology Vol.30 No.8
<P>In this study, the degradation of different cathode carbon supports is investigated in proton exchange membrane fuel cells (PEMFCs). A platinum catalyst is synthesized using various carbon supports, such as Vulcan XC-72, graphite nanopowder and carbon nanotube, which are evaluated based on the fabrication of membrane electrode assemblies. During the startup and shutdown of PEMFCs, the individual electrode potential can be measured <I>in situ</I> using a dynamic hydrogen electrode. The cathode potential increases instantaneously to 1.4 V in one attempt, when H<SUB>2</SUB>/air boundaries are developed on the anode side during the fuel starvation, leading to significant carbon corrosion. The corrosion rates of various carbon supports are calculated from the concentration of gases, such as CO<SUB>2</SUB>, CO and SO<SUB>2</SUB>, emitted from the cathode outlet, measured directly <I>in situ</I> by Fourier transform infrared gas analysis. The carbon nanotube-supported Pt catalyst shows the best performance against carbon corrosion during fuel starvation, compared to commercial Pt/C catalyst and other types of carbon supports.</P>
Nickel oxalate nanostructures for supercapacitors
Jung, Insoo,Choi, Jinsub,Tak, Yongsug Royal Society of Chemistry 2010 Journal of materials chemistry Vol.20 No.29
<P>Herein, we describe a facile method to produce nickel oxalate nanostructures by chemical reaction of oxalic acid and a nickel foil in various organic solvents and water. Grass-like structures consisting of nickel oxalate are produced by the chemical reaction within 30 min for all solvents. Interestingly, nickel oxalate nanowires can be produced by the addition of a small amount of water in certain solvents. Annealing of nickel oxalate structures leads to formation of nickel oxide structures with a slight morphological change. Compositions of the nanostructures are investigated by TEM and FT-IR analyses. In addition, the supercapacitance of the nickel oxalate nanostructures is characterized, and the results show that they are superior to that of nickel oxide nanostructures.</P> <P>Graphic Abstract</P><P>The supercapacitance of the nickel oxalate structures, which are obtained by the immersion of nickel foils in organic solvents containing oxalic acid, is superior to that of the nickel oxide structures, which are produced by the annealing of the nickel oxalate structures. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm00279h'> </P>
Cyclic voltammetry for monitoring bacterial attachment and biofilm formation
Kang, Junil,Kim, Taeyoung,Tak, Yongsug,Lee, Joon-Hee,Yoon, Jeyong Elsevier 2012 Journal of industrial and engineering chemistry Vol.18 No.2
<P><B>Abstract</B></P><P>The early detection of bacterial attachment is very crucial in the prevention of biofilm growth because fully established biofilms are extremely resistant to chemical or physical treatments. The cyclic voltammentry was employed to differentially monitor bacterial attachment and biofilm formation on electrodes in this study. In addition, the mathematical estimation of the surface coverage from the cyclic voltammogram was tried and it was found that the estimation had a linear relationship with the actual coverage of the electrode, validating the potential of cyclic voltammetry for getting the quantitative information about the degree of the bacterial attachment on the surface.</P>
Controlling the Diameter of Cu₂O Nanowires by Electrodeposition
Lee, Jaeyoung,Oh, Jaeho,Tak, Yongsug 한국공업화학회 2004 Journal of Industrial and Engineering Chemistry Vol.10 No.6
Cuprous oxide (Cu₂O) nanowires were prepared by electrodeposition into a porous alumina template. To deposit the Cu₂O nanowires defect-free into the alumina membrane, a cathodic current density of -0.5 ㎃/㎠ was constantly applied in a copper sulfate electrolyte in the presence of lactic acid. Top-view and cross-sectional observations by TEM and SEM showed homogeneous filling of the Cu₂O nanowires in the 100- and 200-㎚ alumina pores. The length of the Cu₂O nanowires was 4 ㎛. EDS data indicated pure Cu₂O and XRD analysis showed preferential growth of Cu₂O (200) and (111) nanowires in the absence of Cu metal and CuO.
Hypostatic instability of aluminum anode in acidic ionic liquid for aluminum-ion battery
Lee, Danbi,Lee, Gibaek,Tak, Yongsug IOP 2018 Nanotechnology Vol.29 No.36
<P>Aluminum-ion batteries are considered to be a promising post lithium-ion battery system in energy storage devices because aluminum is earth-abundant, has a high theoretical capacity, and is of low cost. We report on the chemical activities and stabilities of chloroaluminate anions [Al<I> <SUB>n</SUB> </I>Cl<SUB> <I>n</I>+1</SUB>]<SUP>−</SUP> with aluminum metal using a different mole ratio of AlCl<SUB>3</SUB> and 1-ethyl-3-methylimidazolium chloride. The morphological changes in the Al metal surface are investigated as a function of dipping time in electrolyte, revealing that the Al metal surface is locally attacked by chloroaluminate anions followed by the formation of a new Al oxide layer with a specific lattice plane and a craterlike surface around the cracking site. The aluminum-ion battery exhibits outstanding cycle life and capacity even at the high C-rate of 3 A g<SUP>−1</SUP>, with a high energy efficiency of 98%, regardless of the differences in the size of chloroaluminate anions.</P>
Ko, Eunseong,Choi, Jinsub,Okamoto, Koichi,Tak, Yongsug,Lee, Jaeyoung WILEY‐VCH Verlag 2006 CHEMPHYSCHEM -WEINHEIM- Vol.7 No.7
<P><B>Abstract</B></P>10.1002/cphc.200600060.abs<P>Cu<SUB>2</SUB>O nanowires, mainly consisting of (100) and (200) polycrystalline structures with a length of 4 μm are prepared by electrochemical deposition using a porous alumina template. It is found that the optimized electrochemical conditions to prepare Cu<SUB>2</SUB>O nanowires are different from those for the formation of a bulk thin Cu<SUB>2</SUB>O layer since different pH values are found between the tip of the pores and the bulk, due to diffusion limits in porous alumina with an extremely high aspect ratio of 300. We point out that Cu<SUB>2</SUB>O (200), Cu<SUB>2</SUB>O (111), Cu, and co‐deposited alloys can be obtained under specific electrochemical conditions. In addition, the optical band gap of the prepared Cu<SUB>2</SUB>O nanowires with a length of 4 μm and a diameter of 200 nm is estimated to be 2.17 eV from photoluminescence measurements.</P>