• 전기화학회지
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• 제4권1호
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• pp.26-33
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• 2001

프랙탈 기하학의 계면 전기화학에로의 응용과 관련하여 프랙탈 전극의 임피던스 거동에 대하여 다루었다. 우선, 전기화학적 임피던스 측정시에 자주 관찰되는 constant phase element (CPE)를 간략히 설명하였고, 이와 관련하여 de Levie가 제안한 transmission line model에 대하여 다루었다. CPE현상의 해석을 위하여 Nyikos 와 Pajkossy가 제안한 프랙탈 기하학을 이용한 접근 방법을 소개하였고, 또한 프랙탈 차원과 CPE exponent 사이의 관계를 이론적으로 유도하였다 마지막으로 rough혹은 porous전극의 임피던스 거동을 설명하기 위해 제안된 여러 가지 프랙탈 모델들에 대하여 설명하였다.

• Journal of Electrochemical Science and Technology
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• 제6권2호
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• pp.50-58
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• 2015

There is a great deal of current interest in the development of rechargeable batteries with high energy storage capability due to an increasing demand for electric vehicles (EVs) with driving ranges comparable to those of gasoline-powered vehicles. Among various types of batteries under development, a Li-O₂ battery delivers the highest theoretical energy density; thus, it is considered a promising energy storage technology for EV applications. Despite the fact that extensive research efforts have been made in the field of Li-O₂ batteries in recent years, there are still many technical challenges to be addressed, such as low round-trip efficiency, poor reversibility, and poor power capability. In this article, we provide a short review on the fundamental electrochemistry of Li-O₂ batteries with non-aqueous electrolytes and on electrode materials that have been employed in cathodes (oxygen electrodes). The major aim of this mini-review is to highlight the physical and electrochemical origins of scientific challenges facing Li-O₂ battery technology and to overview the strategies proposed to overcome them.

• Journal of Electrochemical Science and Technology
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• 제8권3호
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• pp.244-249
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• 2017

This paper presents the results of an investigation into the isoamperic point of cyclic voltammograms, which is defined as the singular point where the voltammograms of various scan rates converge. The origin of the unique point is first considered from a theoretical perspective by formulating the voltammetric curves as a system of linear equations, the solution of which indicates that a trivial solution is only available at the potential at which the net current is zero during the reverse potential scan. In addition, by way of a mathematical formulation, it was also shown that the isoamperic point is dependent on the switching potential of the potential scanning. To validate these findings, theoretical and practical cyclic voltammmograms were studied using finite-element based digital simulations and 3-electrode cell experiments. The new understanding of the nature of the isoamperic point provides an opportunity to measure the charge transfer effects without the influence of the mass transfer effects when determining the thermodynamic and kinetic characteristics of a faradaic system.

• Journal of Electrochemical Science and Technology
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• 제12권4호
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• pp.453-457
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• 2021

Lithium-sulfur (Li-S) batteries are one of attractive energy conversion and storage system based on high theoretical specific capacity and energy density with low costs. However, volatile nature of elemental sulfur is one of critical problem for their practical acceptance in industry because it considerably affects electrode uniformity during electrode manufacturing. In this work, polymeric sulfur composite consisting of ionic liquid (IL) are suggested to reduce volatility nature of elemental sulfur, resulting in better processibility of the Li-S cell. According to systematic spectroscopic analysis, it is found that polymeric sulfur is consisting of repeating units combining with elemental sulfur and volatility of them is negligible even at high temperature. In addition, the IL-embedded polymeric sulfur shows moderate cycle performance compared to the cell with elemental sulfur. From these results, it is found that the IL-embedded polymeric sulfur composite is applicable cathode candidate for the Li-S cell based on their excellent non-volatility as well as their superior electrochemical performance.

• Journal of Electrochemical Science and Technology
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• 제7권4호
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• pp.293-297
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• 2016

Here we propose a new equation by which we can estimate the baseline for measuring the peak current of the reverse curve in a cyclic voltammogram. A similar equation already exists, but it is a linear algebraic equation that over-simplifies the voltammetric curve and may cause unpredictable errors when calculating the baseline. In our study, we find a quadratic algebraic equation that acceptably reflects the complexity included in a voltammetric curve. The equation is obtained from a laborious numerical analysis of cyclic voltammetry simulations using the finite element method, and not from the closed form of the mathematical equation. This equation is utilized to provide a virtual baseline current for the reverse peak current. We compare the results obtained using the old linear and new quadratic equations with the theoretical values in terms of errors to ascertain the degree to which accuracy is improved by the new equation. Finally, the equations are applied to practical cyclic voltammograms of ferricyanide in order to confirm the improved accuracy.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.112-112
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• 2011

The interaction of water molecules with solid surfaces has been a subject of considerable interests, due to its importance in the fields from atmospheric and environmental phenomena to biology, catalysis and electrochemistry [1,2]. Among various kinds of surfaces, a lot of theoretical and experimental studies have been performed regarding water on MgO(100), however, to date, there has been no direct observation of water molecules on MgO by scanning tunneling microscope (STM) as compared with those on metal surface. Here, we will present the direct observation and manipulation of single water molecules on ultrathin MgO(100) films using low-temperature scanning tunneling microscope (LT-STM) [3]. Our results rationalize the previous theoretical predictions of isolated water molecules on MgO including the optimum adsorption sites and non-dissociative adsorption of water. Moreover, we were able to dissociate a water molecule by exciting the vibrational mode of water, which is unattainable on metal surfaces. The enhanced residual time of tunneling electrons in molecules on the insulating film is responsible for this unique pathway toward dissociation of water.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2871-2876
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• 2022

The sensitivity of polymer-based capacitive relative humidity (RH) sensors after irradiation with neutrons, electrons and protons was measured. Degradation consists of the decreasing of the upper RH limit that can be measured. At the same time, low RH-level sensitivity is almost stable. After 30 krad of absorption dose, RH cut off is equal to 85% of max value, after 60 krad-40%. Degradation reduces after annealing which indicates high radiation sensitivity of the internal circuit in comparison to RH-sensing polymer film.

• 세라미스트
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• 제21권2호
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• pp.49-58
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• 2018

Metal oxide based materials have been widely used to fields of electrochemical applications. Recently, various type of defects from microstructures of metal oxides and their nanocomposites have been raised as the important material design factors for realizing highly improved electrochemical properties. Previous experimental and theoretical works have suggested that controlling the reaction activity and kinetics of the key electrochemical reactions by activated interfaces originating from the defect sites can play an important role in achieving the robust energy storage and conversion. Therefore, this paper focuses on the role of defect-controlled metal oxide materials such as doping, edge-sites, grain boundaries and nano-sized pores for the high performances in energy storage devices and electrocatalysts. The research approaches demonstrated here could offer a possible route to obtain noble ideas for designing the metal oxide materials for the energy storage and conversion applications.

• 전기화학회지
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• 제5권4호
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• pp.216-220
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• 2002

The effects of electrolytes on electrochemical behavior from an oil thin layer interposed between a graphite electrode and an aqueous solution phase were examined. A hydrophobic electroactive species, tetrachloro-1,4-benzoquinone (TCQ), in a benzonitrile (EN) layer was employed to study ion transfer properties across the BN-water interface. Experimental results showed that hydrophobic cations as well as anions could be successfully used as ionic charge carriers. The addition of various salts into either the oil layers or the aqueous solutions offers deeper insight for the electrochemistry of the liquid thin layer system. When aqueous perchloric acid is interfaced with the BN films, the perchlorate ion of tetrahexylammonium perchlorate (THAP) substantially suppresses the dissociated proton concentration in the layer by the common ion effect while there is only a little change in the total acid concentration. Further approach by theoretical calculation makes it possible to quantitatively understand the effect of the electrolytes to the electrochemical responses of TCQ, which were previously reported (Anal. Chem. 73, 337 (2001)).

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1900-1906
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• 2012

Three carbazole chromophores featuring dicyano, cyano, ethyl acetate and dimethyl acetate groups as an acceptor moiety with a ${\pi}$-conjugated spacer and $N$-methyl dibenzo[$b$]pyrole as donor were synthesized by Knovenagel condensation and characterized by IR, $^1HNMR$, $^{13}CNMR$, UV-vis, fluorescence spectroscopy, electrochemistry and theoretical B3LYP/6-$311G^*$ level whilst NLO properties and spectroscopic quantities were calculated. Calculations showed remarkable trend with HOMO located on the donor moiety and LUMO on the acceptors dicyano methylene, cyano, ethyl acetate methylene and dimethyl acetate methylene. In agreement with the calculations, solvatochromic, behavior intramolecular charge transfer band was observed in the visible region.