• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.408-412
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• 2019

In this study, nitrogen doped carbon felt was prepared by pyrolysis of urea at high temperature and applied as an electrode for vanadium redox flow cell. Urea is easier to handle than ammonia and forms $NH_2$ radicals at higher temperatures, creating a nitrogen functional group on the carbon surface and acting as an active site in the vanadium redox reaction. Therefore, the discharge capacity of activated carbon felt electrodes using urea was 14.9 Ah/L at a current density of $150mA/cm^2$, which is 23% and 187% higher than OGF and GF, respectively. These results show the possibility that activated carbon felt electrode using urea can be used as electrode material for redox flow battery.

• Analytical Science and Technology
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• v.8 no.4
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• pp.887-894
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• 1995

Toward the development of universal, sensitive, and convenient method of DNA (or RNA) detection, two kinds of electrochemically active DNA ligands. acridine - viologen and oligonucleotide - ferrocene conjugate, were prepared. Thermodynamic and electrochemical study revealed that these probes bound strongly to DNA, and showed a typical cyclic voltammograms, indicating a potential for use as a reversible electrochemical labelling agent for DNA. Especially, using the electrochemically active oligonucleotide, we have been able to demonstrate the detection of DNA at femtomole levels by HPLC equipped with ordinary electrochemical detector (ECD). These results lead to the conclusion that the redox-active probes are very useful for the microanalysis of nucleic acid due to the stabilily of the complexes, high detection sensitivity, and wide applicability to the target structures (single- and double strands) and sequences.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.847-852
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• 2019

In this study, the effect of additives on the performance of aqueous organic redox flow battery (AORFB) using quinoxaline and ferrocyanide as active materials in alkaline supporting electrolyte is investigated. Quinoxaline shows the lowest redox potential (-0.97 V) in KOH supporting electrolyte, while when quinoxaline and ferrocyanide are used as the target active materials, the cell voltage of this redox combination is 1.3 V. When the single cell tests of AORFBs using 0.1 M active materials in 1 M KCl supporting electrolyte and Nafion 117 membrane are implemented, it does not work properly because of the side reaction of quinoxaline. To reduce or prevent the side reaction of quinoxaline, the two types of additives are considered. They are the potassium sulfate as electrophile additive and potassium iodide as nucleophilie additive. Of them, when the single cell tests of AORFBs using potassium iodide as additive dissolved in quinoxaline solution are performed, the capacity loss rate is reduced to $0.21Ah{\cdot}L^{-1}per\;cycle$ and it is better than that of the single cell test of AORFB operated without additive ($0.29Ah{\cdot}L^{-1}per\;cycle$).

• Journal of Soil and Groundwater Environment
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• v.25 no.1
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• pp.25-36
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• 2020

In a redox transition zone, geochemical reactions are facilitated by active bacteria that mediate reactions involving electrons, and arsenic (As) and iron (Fe) cycles are the major electron transfer reactions occurring at such a site. In this study, the effect of repetitive redox changes on soil bacterial community in As-contaminated soil was investigated. The results revealed that bacterial community changed actively in response to redox changes, and bacterial diversity gradually decreased as the cycle repeated. Proportion of strict aerobes and anaerobes decreased, while microaerophilic species such as Azospirillum oryzae group became the predominant species, accounting for 72.7% of the total counts after four weeks of incubation. Bacterial species capable of reducing Fe or As (e.g., Clostridium, Desulfitobacterium) belonging to diverse phylogenetic groups were detected. Indices representing richness (i.e., Chao 1) and phylogenetic diversity decreased from 1,868 and 1,926 to 848 and 1,121, respectively. Principle component analysis suggests that repetitive redox fluctuation, rather than oxic or anoxic status itself, is an important factor in determining the change of soil bacterial community, which in turn affects the cycling of As and Fe in redox transition zones.

• Journal of the Korean Electrochemical Society
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• v.7 no.4
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• pp.167-172
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• 2004

3,4-dihydroxybenzaldehyde(3,4-DHB) was oxidatively el electropolymerized on glassy carbon (GC) electrodes to prepare CC/p-3,4-DHB type electrodes, which were subsequently modified with 3,4-dihydroxybenzoic acid(3,4-DHBA) using 0.05M HCI as a catalyst. The esterification reactions were performed between -OH sites on the polymeric film surface of the p-3,4-DHB and the -COOH sites within the 3,4-DHBA molecules in solution. These reactions had a rate constant value of $1.1\times10^{-1}\;s^{-1}$ for the esterification step as obtained from the first-order rate constant in the solution. The electrochemical responses of the GC/p-3,4-DHB-3,4-DHBA electrodes exert an influence upon the buffer solution, its pH and applied potential ranges. The redox process of the electrode was more easily controlled by charge transfer kinetics than that of the CC/p-3,4-DHB. The modified electrodes had redox active sites that were 10 times more active than those present before modification. The electrical admittance of the modified electrodes was also three times higher than that of the unmodified electrodes. After being annealed in ethanol for 20 hrs the electrodes brought about a 3.3 times greater change of water molecules in the redox reaction. The modified electrodes are stable in the potential range of 0.4 to 0.55V.

• BMB Reports
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• v.31 no.5
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• pp.444-452
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• 1998

The visible spectra of soybean ferric leghemoglobin reductase exhibited a charge transfer band at 530 nm under aerobic condition. Spectra of the oxidized enzyme show a flavin peak at 454 nm and the enzyme has three redox states associated with the active site of the enzyme. The enzyme has an active disulfide bridge and two-electron transfer may dominate in the ferric state of leghemoglobin reduction. The midpoint potentials of the enzyme were determined by spectrotitration to be -0.294 V for disulfide/dithiol and -0.318 V for FAD/$FADH_2$. Since the midpoint potentials for $NAD^+$/NADH and the ferrous/ferric states of leghemoglobin are -0.32 V and +0.22 V, respectively, it is proposed that two electrons are transferred sequentially from NADH to FAD, to the disulfide group, and then to the ferric state of leghemoglobin in the enzyme reaction.

• Journal of the Korean Electrochemical Society
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• v.10 no.1
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• pp.43-47
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• 2007

Electrochemical rectification at electrode chemically modified with redox active agents isolated at monolayer level was considered. Formulation of the rising part of linear sweep voltammogram at steady and rotating disc electrode was introduced.

• Bulletin of the Korean Chemical Society
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• v.33 no.4
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• pp.1190-1198
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• 2012

Three hydroquinone dimethyl ether derivatives have been synthesized and characterized by X-ray diffraction. The electron donating properties were evaluated by using UV-vis spectroscopy, cyclic voltammetry and by ESR spectroscopy. The microcrystalline cation-radical salts of the three donor molecules were also isolated by using antimony pentachloride, a single electron Lewis acid oxidant.

• Journal of Electrochemical Science and Technology
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• v.10 no.2
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• pp.170-176
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• 2019

Alkanethiol self-assembled monolayers (SAMs) and partially ferrocene (Fc) modifications were applied to the Au ultramicroelectrode (UME) rather than to standard sized electrodes with dimension of millimeters. The electron transfer mediation of the SAMs and Fc modified Au UME was investigated by using a p-aminophenol (p-AP) oxidation reaction via cyclic voltammetry. The electrocatalytic p-AP oxidation at the SAMs and Fc modified Au UME showed a much larger electrocatalytic current density than that at the standard sized electrode due to the fast mass transfer rate at the UME.

• Journal of the Korean institute of surface engineering
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• v.52 no.3
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• pp.150-155
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• 2019

The carbon electrode was modified through manganese-catalyzed hydrogenation method for high energy density vanadium redox flow battery (VRFB). During the catalytic hydrogenation, the manganese oxide deposited at the surface of the carbon electrode stimulated the conversion reaction from carbon to methane gas. This reaction causes the penetration of the manganese and excavates a number of cavities at electrode surface, which increases the electrochemical activity by inducing additional electrochemically active site. The formation of the porous surface was confirmed by the scanning electron microscopy (SEM) images. Finally, the electrochemical performance test of the electrode with the porous surface showed lower polarization and high reversibility in the cathodic reaction compared to the conventional electrode.