• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.1
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• pp.84-87
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• 2016

In this paper, a receiver for wireless power transfer is proposed. The receiver consists of a 100 W rectifier in 1.8 MHz frequency band, and a constant current charger. In particular, two kinds of protection circuits are installed in the rectifier. They are a over-voltage protection circuit which block the input voltages greater than 30 V and a active-dummy load which maintains the receiver input impedance by automatically consuming the remaining input power. The constant current charger is designed to charge the battery with a charging current of up to 1 A. A wireless charging system is fabricated using the proposed receiver. The system is composed of a 130 W transmitter, two magnetic resonator, and proposed receiver for charging a 48 V Li-Ion battery using the coupled magnetic resonance method. By the measurement result, the system efficiency is about 54 %.

• Journal of the Korea Society of Computer and Information
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• v.26 no.11
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• pp.11-19
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• 2021

In this paper, we propose a prototype platform combined with the power management system using, as an auxiliary power storage device, a supercapacitor that can be fast charged and discharged with high power efficiency as well as semi-permanent charge and discharge cycle life. For the proposed platform, we designed a technique which is capable of detecting the state of power cutoff or resumption of power supplied from the solar panel in accordance with physical environment changes through an interrupt attached to the micro-controller was developed. To prevent data loss in a computing environment in which continuous power supply is not guaranteed, we implemented a low-level system software in the micro-controller to transfer program context and data in volatile memory to nonvolatile memory when power supply is cut off. Experimental results shows that supercapacitors effectively supply temporary power as auxiliary power storage devices. Various benchmarks also confirm that power state detection and transfer of program context and data from volatile memory to nonvolatile memory have low overhead.

• Journal of Energy Engineering
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• v.29 no.2
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• pp.1-9
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• 2020

In recent days, fuel cell has received attention from the world as an alternative power source to hydrocarbon used in automobile engines. With the industrial advances of fuel cell, There have been a lot of researches actively conducted to find a way of generating hydrogen. Among many hydrogen production methods, Solid Oxide Electrolysis Cell(SOEC) is not only a basic way but also environment-friendly method to produce hydrogen gas. Solid Oxide Electrolysis Cell has lower electrical energy demands and high thermal efficiency since it is possible to operate under high temperature and high pressure conditions. For these reasons, experimental researches as well as studies on numerical modeling for Solid Oxide Electrolysis Cell have been under way. However, studies on numerical modeling are relatively less enough than experimental accomplishments and have limited performance prediction, which mostly is considered as a result from inadequate effects of electrochemical properties by temperature and pressure. In this study, various experimental studies of commercial Membrane Electrode Assembly (MEA) composed of Ni-YSZ (40wt%, Ni-60 wt% YSZ)/8-YSZ (TOSOH, TZ8Y)/LSM (La_0.9Sr_0.1MnO₃) was utilized for improving effectiveness of SOEC model. After numerically analyzing effects of electrochemical properties according to operating temperature, causing the largest deviation between experiments and simulation are that Charge Transfer Coefficient (CTC), exchange current density, diffusion coefficient, electrical conductivity in SOEC. Analyzing temperature effect on parameter used in overpotential model is conducted for modeling of SOEC. cross-validation method is adopted for application of various MEA and evaluating feasibility of model. As a result, the study confirm that the numerical model of SOEC based on structured process of effectiveness evaluation makes performance prediction better.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.2
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• pp.187-192
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• 2019

Hybrid power storage system with emergency power function for demand management and power outage minimizes the investment cost in the building of buildings and factories requiring emergency power generation facilities, We propose a new business model by developing technology that can secure economical efficiency by reducing power cost at all times. Normally, system power is supplied to load through STS (Static Transfer Switch), and PCS is connected to system in parallel to perform demand management. In order to efficiently operate the electric power through demand forecasting, the EMS issues a charge / discharge command to the ESS as a PMS (Power Management System), and the PMS transmits the command to the PCS controller to operate the system. During the power outage, the STS is rapidly disengaged from the system, and the PCS becomes an independent power supply and can supply constant voltage / constant frequency power to the load side. Therefore, it is possible to secure reliability through verification of actual system linkage and independent operation performance of hybrid ESS, By enabling low-carbon green growth technology to operate in conjunction with an efficient grid, it is possible to improve irregular power quality and contribute to peak load by generating renewable energy through ESS linkage. In addition, the ESS is replacing the frequency follow-up reserve, which is currently under the charge of coal-fired power generation, and thus it is anticipated that the operation cost of the LNG generator with high fuel cost can be reduced.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1627-1637
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• 2012

The coupling reaction between 5-bromo-3-phenylbenzo[c]isoxazole and diphenylamine followed by further condensation with a mono-, di- or ter-acetyl aromatic compound in the presence of diphenyl phosphate at $145^{\circ}C$ gave a novel asymmetric diarylquinolines, oligoquinolines with diphenylamine endgroups, and a first generation quinoline dendrimer in 41-82% isolated yield. The electrochemical and photophysical properties of the oligoquinolines were characterized by cyclic voltammograms (CVs) and spectroscopy. All the quinolines emit bright sky blue light due to charge transfer from quinoline group to diphenly amine with very high quantum efficiency (> 90%). Organic light-emitting diodes (OLEDs) were fabricated using these quinolines as emitting materials. Among different device architectures explored, OLEDs with a structure of ITO/PEDOT (40 nm)/TAPC (15 nm)/D-A quinoline (40 nm)/TPBI (30 nm)/LiF (1 nm)/Al using TAPC as an electron blocking layer and TPBI as a hole blocking layer gave the best performance. A high external quantum efficiency in the range of 1.2-2.3% were achieved in all the quinolines with the best performance in BBQA(5). Our results indicate diarylamino-substituted oligoquinoline and dendrimer are promising materials for OLEDs applications.

• Korean Journal of Materials Research
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• v.28 no.1
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• pp.68-74
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• 2018

Cobalt-incorporated zeolitic imidazolate framework ZIF-8 was synthesized by a simple one-pot synthesis method at room temperature. Powder X-ray diffraction patterns and energy dispersive X-ray spectrum confirmed the formation of the bimetallic Co/Zn-ZIF structure. UV-Vis diffuse reflectance spectra revealed that the bimetallic ZIF had a lower HOMO-LUMO gap compared with ZIF-8 due to the charge transfer process from organic ligands to cobalt centers. A hydrolytic stability test showed that Co/Zn-ZIF is very robust in aqueous solution - the most important criterion for any material to be applied in photodegradation. The photocatalytic efficiency of the synthesized samples was investigated over the Indigo Carmine (IC) dye degradation under solar simulated irradiation. Cobalt incorporated ZIF-8 exhibited high efficiency over a wide range of pH and initial concentration. The degradation followed through three distinct stages: a slow initial stage, followed by an accelerated stage and completed with a decelerated stage. Moreover, the photocatalytic performance of the synthesized samples was highly improved in alkaline environment rather than in acidic or neutral environments, which may have been because in high pH medium, the increased concentration of hydroxyl ion facilitated the formation of hydroxyl radicals, a reactive species responsible for the breaking of the Indigo Carmine structure. Thus, Co/Zn-ZIF is a promising and green material for solving the environmental pollution caused by textile industries.

• Membrane Journal
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• v.29 no.6
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• pp.299-307
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• 2019

Photocatalysis is an environment friendly technique for degrading organic dyes in water. Tungsten oxide is becoming an active area of research in photocatalysis nanomaterials for having a smaller bandgap than the previously favored titanium dioxide. Synthesis of hierarchical structures, doping platinum (Pt), coupling with nanocomposites or other semiconductors are investigated as valid methods of improving the photocatalytic degradation efficiency. These impact the reaction by creating a redshift in the wavelength of light used, effecting charge transfer, and the formation/recombination of electron-hole pairs. Each of the methods mentioned above are investigated in terms of synthesis and photocatalytic efficiency, with the simplest being modification on the morphology of tungsten oxide, since it does not need synthesis of other materials, and the most efficient in photocatalytic degradation being complex coupling of metal oxides and carbon composites. The photocatalysis technology can be incorporated with water purification membrane by modularization process and applied to advanced water treatment system.

• Korean Journal of Optics and Photonics
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• v.31 no.1
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• pp.37-44
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• 2020

In this study, we propose a design method to optimize the electro-optical efficiency of a planar solar cell structure by adjusting one-dimensionally periodic emitter electrodes. Since the aperture ratio of the active layer decreases as the period of the emitter electrode decreases, the amount of light absorption diminishes, affecting the performance of the device. Here we design the optimal structure of the periodic emitter electrode in a simple planar solar cell, by simulation. In terms of optics, we find the condition that shows optical performance similar to that of a reference without the emitter electrode. In addition, the optimized electrode structure is extracted considering both the optical and electrical efficiency. This work will help to increase the utilization of solar cells by suggesting a structure that can most efficiently transfer charge generated by photoelectric conversion to the electrodes.

• Korean Journal of Materials Research
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• v.31 no.10
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• pp.552-561
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• 2021

For the purpose of manufacturing a high efficiency TiO₂ photocatalyst, B-doped TiO₂ photocatalysts are synthesized using a plasma electrolytic oxidation method in 0.5 M H₂SO₄ electrolyte with different concentrations of H₃BO₃ as additive. For the B doped TiO₂ layer fabricated from sulfuric electrolyte having a higher concentration of H₃BO₃ additive, the main XRD peaks of (101) and (200) anatase phase shift gradually toward the lower angle direction, indicating volume expansion of the TiO₂ anatase lattice by incorporation of boron, when compared with TiO₂ layers formed in sulfuric acid with lower concentration of additive. Moreover, XPS results indicate that the center of the binding energy peak of B1s increases from 191.45 eV to 191.98 eV, which suggests that most of boron atoms are doped interstitially in the TiO₂ layer rather than substitutionally. The B doped TiO₂ catalyst fabricated in sulfuric electrolyte with 1.0 M H₃BO₃ exhibits enhanced photocurrent response, and high efficiency and rate constant for dye degradation, which is ascribed to the synergistic effect of the new impurity energy band induced by introducing boron to the interstitial site and the improvement of charge transfer reaction.

• Journal of the Korean GEO-environmental Society
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• v.23 no.3
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• pp.23-29
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• 2022

In this study, we investigated the ozone nanobubble process in which nanobubble and ultrasonic cavitation were applied simultaneously to improve the dissolution and self-decomposition of ozone. To confirm the organic decomposition efficiency of the process, a 200 mm × 200 mm × 300 mm scale reactor was designed and phenol decomposition experiments were conducted. The use of nanobubble was 2.07 times higher than the conventional ozone aeration in the 60 minutes reaction and effectively improved the dissolution efficiency of ozone. Ultrasonic irradiation increased phenol degradation by 36% with nanobubbles, and dissolved ozone concentration was lowered due to the promotion of ozone self-decomposition. The higher the ultrasonic power was, the higher the phenol degradation efficiency. The decomposition efficiency of phenol was the highest at 132 kHz. The ozone nanobubble process showed better decomposition efficiency at high pH like conventional ozone processes but achieved 100% decomposition of phenol after 60 minutes reaction even at neutral conditions. The effect by pH was less than that of the conventional ozone process because of self-decomposition promotion. To confirm the change in bubble properties by ultrasonic irradiation, a Zetasizer was used to measure the bubbles' size and zeta potential analysis. Ultrasonic irradiation reduced the average size of the bubbles by 11% and strengthened the negative charge of the bubble surface, positively affecting the gas transfer of the ozone nanobubble and the efficiency of the radical production.