• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.68-74
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• 2021

Gas diffusion layer (GDL) compression is important parameter of polymer electrolyte membrane fuel cell (PEMFC) performance to have an effect on contact resistance, reactants transfer to electrode, water content in membrane and electrode assembly (MEA). In this study, the effect of GDL compression on fuel cell performance was investigated for commercial products, JNT20-A3. Polarization curve and electrochemical impedance spectroscopy was performed at different relative humidity and compression ratio using electrode area of 25 ㎠ unit cell. The contact resistance was reduced to 8, 30 mΩ·㎠ and membrane hydration was increased as GDL compression increase from 18.6% to 38.1% at relative humidity of 100 and 25%, respectively. It was identified through ohmic resistance change at relative humidity conditions that as GDL compression increased, water back-diffusion from cathode and electrolyte membrane hydration was increased because GDL porosity was decreased.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.62-69
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• 2022

Graphene has a large surface area to volume ratio and good mechanical and electrical property and biocompatibility. This study described the electrochemical deposition and reduction of graphene oxide on the surface of indium tin oxide (ITO) glass slide and electrochemical characterization of graphen-modified ITO. Cyclic voltammetry was used for the deposition and reduction of graphene oxide. The surface of graphen-coated ITO was characterized using scanning electron microscopy and energy dispesive X-ray spectroscopy. The electrodes were evaluated by performing cyclic voltammetry and electrochemical impedance spectroscopy. The number of cycles and scan rate greatly influenced on the coverage and the degree of reduction of graphene oxide, thus affecting the electrochemical properties of electrodes. Modification of ITO with graphene generated higher current with lower charge transfer resistance at the electrode-electrolyte interface. Glucose oxidase was immobilized on the graphene-modified ITO and has been found to successfully generate electrons by oxidizing glucose.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.4_1
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• pp.493-504
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• 2022

Recently, as interest in eco-friendliness grows, the supply of hybrid electric vehicles and pure electric vehicles (EVs) for improving fuel efficiency of automobiles is rapidly expanding. The average daily energy consumption of electric vehicles is less than 20 [%] of the total ESS capacity of the vehicle, and research on additional functions using the ESS of the vehicle is urgently needed to expand the supply of electric vehicles. V2H(Vehicle to Home), like V2G(Vehicle to Grid), includes the concept of cooperating with system stabilization using ESS of electric vehicles. In addition, it includes various operations that can realize home welfare, such as uninterrupted power supply in case of power outage at home, and power supply for home DC devices. Therefore, in order to expand the supply of eco-friendly electric vehicles, it is urgently required to develop a V2H system with various functions that can realize home welfare. In this paper, we propose a V2H system with a CLLC resonant converter and a non-isolated step-up converter that can solve different impedance and resonant frequencies depending on the power transfer direction. The proposed V2H system is 6 [kVA] applicable to 150-450 [V], the voltage range that can use the ESS voltage for electric vehicles, and is designed with a capacity that can handle instantaneous electricity use at home. In addition, in order to verify the feasibility, an experiment by Psim simulation and prototype production was performed.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.52-57
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• 2023

This study is a basic research for the development of high performance flexible electrode material. To enhance its electrochemical property, CuO nanoparticles (CuO NPs) were introduced and dispersed on surface of CNT fiber through electrochemical deposition method. The CNT fiber/CuO NPs electrode was fabricated and applied to electrochemical non-enzymatic glucose sensor. Surface morphology and elemental composition of the CNT fiber/CuO NPs electrode was characterized by scanning electron microscope (SEM) with energy dispersive X-ray spectrometry (EDS). And its electrochemical characteristics were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The CNT fiber/CuO NPs electrode exhibited the good sensing performance for glucose detection such as high sensitivity, wide linear range, low detection limit and good selectivity due to synergetic effect of CNT fiber and CuO NPs. Based on the unique property of CNT fiber, CuO NPs were provide large surface area, enhanced electrocatalytic activity, efficient electron transport property. Therefore, it is expected to develop high performance flexible electrode materials using various nanomaterials.

• Journal of Electrochemical Science and Technology
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• v.14 no.4
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• pp.361-368
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• 2023

In lithium-sulfur (Li-S) batteries, encapsulation of sulfur in activated carbon (AC) materials is a promising strategy for preventing the dissolution of lithium polysulfide into electrolytes and enhancing cycle life, because instead of solid-liquid-solid reactions, quasi-solid-state (QSS) reactions occur in the AC micropores. While a high weight fraction of sulfur in S/AC composites is essential for achieving a high energy density of Li-S cells, the deterioration mechanisms under such conditions are still unclear. In this study, we report the deterioration mechanisms during charge-discharge cycling when the discharge products overflow from the AC. Analysis using scanning electron microscopy and energy-dispersive X-ray spectrometry confirms that the sulfur in the S/AC composites migrates outside the AC as cycling progresses, and it is barely present in the AC after 20 cycles, which corresponds to the capacity decay of the cell. Impedance analysis clearly shows that the electrical resistance of the S/AC composite and the charge-transfer resistance of QSS reactions significantly increase as a result of sulfur migration. On the other hand, the charge-discharge cycling performance under limited-capacity conditions, where the discharge products are encapsulated inside the AC, is extremely stable. These results reveal the degradation mechanism of a Li-S cell with micro-porous carbon and provide crucial insights into the design of a S/AC composite cathode and its operating conditions needed to achieve stable cycling performance.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.95-98
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• 1998

We have developed new type of superconducting-superionic conducting nanohybrids, $Ag_xI_wBi_2Sr_2Ca_{n-1}Cu_nO_y$ (n=1 and 2) by applying the chimie douce reaction to the superconducting Bi-based cuprates. These nanohybrids can be achieved by the stepwise intercalation whereby the $Ag^+$ ion is thermally diffused into the pre-intercalated iodine sublattice of $IBi_2Sr_2Ca_{n-1}Cu_nO_y$. According to the X-ray diffraction analysis, the Ag-I intercalates are found to have an unique heterostructure in which the superionic conducting Ag-I layer and the superconducting $IBi_2Sr_2Ca_{n-1}Cu_nO_y$ layer are regularly interstratified with a remarkable basal increment of ~7.3$\AA$. The systematic XAS studies demonstrate that the intercalation of Ag-I accompanies the charge transfer between host and guest, giving rise to a change in hole concentration of $CuO_2$ layer and to a slight $T_c$ change. The Ag K-edge EXAFS result reveals that the intercalated Ag-I has a $\beta$-AgI-like local structure with distorted tetrahedral symmetry, suggesting a mobile environment for the intercalated $Ag^+$ ion. In fact, from ac impedance analyses, we have found that the Ag-I intercalates possess a fast ionic conductivity ($\sigma_i=10^{-1.4}\sim 10^{-2.6}\Omega^{-1}\textrm{cm}^{-1}\;at\;270^{\circ}C$ with an uniform activation energy ($\DeltaE_a=0.22\pm 0.02$ eV). More interesting finding is that these intercalates exhibit high electronic conducting as well as ionic ones ($t_i$=0.02~0.60) due to their interstratified structure consisting of superionic conducting and superconducting layers. In this respect, these new intercalates are expected to be useful as an electrode material in various electrochemical devices.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.466-473
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• 2013

In this paper, a compact planar multi-loop self-resonant coil of high quality factor with a coaxial cross section is proposed for effective wireless charging. The proposed coil has high Q-factor and a resonant frequency of a coil can be easily controlled by adjusting distributed capacitance. For designing the coil, a self-inductance and a distributed capacitance are calculated theoretically. The self-inductance is calculated from the sum of the mutual energies between small circular loops that are made by dividing the cross section of the coil. To verify its properties and calculation results, the self-resonant coils are fabricated by using a coaxial cable with characteristic impedance of $50{\Omega}$. The measured frequencies are very consistent with the calculated ones. In addition, the resonant frequency can be adjusted slightly by the tuning parameter ${\gamma}$. The resonant coils are applied to a tablet PC, the Q-factors of the Tx and Rx resonant coils are 282 and 135, respectively. As a result of measurement when height between the two resonant coils is 4.4 cm, the power transfer efficiency is more than 80 % within a radius of 5 cm.

• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.729-734
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• 2002

In this study, the polyaniline films of emeraldine base(EB) and lucoemeraldine base(LEB) form chemically doping with poly(sodium-4 styrenesulfonate, PSS) were prepared by casting the mixed solution of chloroform and m-cresol on ITO(indium tin oxide) electrode. By analyzing UV-vis spectra of the mixed solutions, the effects of the secondary doping by m-cresol were obtained. And the conductivity of polyaniline film was increased with increasing m-cresol content. The results suggest that the improvement of conductivity obtained by secondary doping results primarily from interaction of polyaniline and m-cresol. As the results of analyzing cyclic voltammograms, it was known that the redox peak currents of polyaniline electrode prepared from LEB were larger and more reversible than those of polyaniline electrodes prepared from EB. The charge transfer resistances($R_{ct}$) of polyaniline electrodes were reduced with increasing m-cresol content, and LEB/PSS electrodes were smaller than EB/PSS electrodes. This result agrees to the analysis of the redox peak current of cyclic voltammograms. The solution resistance and the capacity of electrical double layer almost unchanged in all prepared polyaniline electrodes. It was confirmed that solution resistance was independent of frequency factor in AC impedance spectra. Also the polyaniline film doping with PSS was revealed pseudo n-type characteristics of conducting polymer.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.1-6
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• 2022

As the demand for wearable devices increases, many studies have been studied on the development of flexible electrode materials recently. In particular, the development of high-performance flexible electrode materials is very important for wearable sensors for healthcare because it is necessary to continuously monitor and accurately detect body information such as body temperature, heart rate, blood glucose, and oxygen concentration in real time. In this study, we fabricated the nonenzymatic glucose sensor based on polyaniline/carbon nanotube fiber (PANI/CNT fiber) electrode. PANI layer was synthesized on the flexible CNT fiber electrode through electrochemical polymerization process in order to improve the performance of a flexible CNT fiber based electrode material. Surface morphology of the PANI/CNT fiber electrode was observed by scanning electron microscopy. And its electrochemical characteristics were investigated by chronoamperometry, cyclic voltammetry, electrochemical impedance spectroscopy. Compared to bare CNT fiber electrode, this PANI/CNT fiber electrode exhibited small electron transfer resistance, low peak separation potential and large surface area, resulting in enhanced sensing properties for glucose such as wide linear range (0.024~0.39 and 1.56~50 mM), high sensitivity (52.91 and 2.24 ㎂/mM·cm²), low detection limit (2 μM) and good selectivity. Therefore, it is expected that it will be possible to develop high performance CNT fiber based flexible electrode materials using various nanomaterials.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.6
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• pp.452-460
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• 2021

As the global electric vehicle (EV) market expands, eco-friendly EV that complement performance and safety problems continue to be released and the market is growing. However, in the case of EVs, the inconvenience of charging, safety problems such as electric shock, and electromagnetic interference (EMI) problems caused by the interlocking of various electronic components are problems that must be solved in EVs. The use of wireless power transmission technology can solve the problem of safety by not dealing with high current and high voltage directly and solving the inconvenience of charging EVs. In this paper, in order to reduce EMI a wireless charging control module, which is a key electronic component of WPT of EV. EMI reduction was designed through simulation of problems such as resonance and impedance that may occur in the power supply and signal distortion between high-speed communication that may occur in the signal part. Therefore, through the EMI reduction design with power integrity and signal integrity, the WPT wireless charging control module for electric vehicles reduces 10 dBu V/m and 15 dBu V/m, respectively, in 800 MHz to 1 GHz bands and 1.5 GHz bnad.