• Korean Chemical Engineering Research
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• v.57 no.4
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• pp.525-530
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• 2019

The performance and stability of solid oxide fuel cells (SOFCs) depend on the microstructure of the electrode and electrolyte. In anode, porosity and pore distribution affect the active site and fuel gas transfer. In an electrolyte, density and thickness determine the ohmic resistance. To optimizing these conditions, using costly method cannot be a suitable research plan for aiming at commercialization. To solve these drawbacks, we made high performance unit cells with low cost and highly efficient ceramic processes. We selected the NiO-YSZ cermet that is a commercial anode material and used facile methods like die pressing and dip coating process. The porosity of anode was controlled by the amount of carbon black (CB) pore former from 10 wt% to 20 wt% and final sintering temperature from $1350^{\circ}C$ to $1450^{\circ}C$. To achieve a dense thin film electrolyte, the thickness and microstructure of electrolyte were controlled by changing the YSZ loading (vol%) of the slurry from 1 vol% to 5 vol. From results, we achieved the 40% porosity that is well known as an optimum value in Ni-YSZ anode, by adding 15wt% of CB and sintering at $1350^{\circ}C$. YSZ electrolyte thickness was controllable from $2{\mu}m$ to $28{\mu}m$ and dense microstructure is formed at 3vol% of YSZ loading via dip coating process. Finally, a unit cell composed of Ni-YSZ anode with 40% porosity, YSZ electrolyte with a $22{\mu}m$ thickness and LSM-YSZ cathode had a maximum power density of $1.426Wcm^{-2}$ at $800^{\circ}C$.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.3
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• pp.117-123
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• 2006

The water quality before and after a typhoon was investigated as a part of a study on the increase of organic matter and on the fundamental measures to counter chemical oxygen demand (COD) in the eutrophic Soho coastal seawaters of Gamak Bay. The dissolved oxygen (DO) saturations were <54% when water column was stratified. The DO saturation was similar at surface and in the bottom layer after a typhoon $(78\sim88%)$, and a very high DO saturation (234%) was observed in the surface water after mass phytoplankton growth. The highest values of $NH_4-N,\;NO_3-N,\;PO_4-P$, and $SiO_2-Si$ were 18.22, 38.90, 1.58, and $52.10{\mu}M$, respectively, when freshwater entered after heavy rainfall events. In addition, high concentrations of $NH_4-N,\;PO_4-P$, and $SiO_2-Si$ were detected with low DO saturations in bottom water (>5m). A maximum chlorophyll (Chl.) concentration of $311.0{\mu}gl^{-1}$ was observed after typhoon, when a high-density Scrippsiella trochoidea red tide occurred with cell density of 42,000 cells $ml^{-1}$. The algal growth potential (AGP) was high after the typhoon. Nitrogen was always a limiting nutrient for phytoplankton growth. The highest COD level was $10.55mgl^{-1}$, and the main reason of the variation in COD was likely to be phytoplankton growth $(r^2=0.612,\;p=0.000)$. Organic matter, which entered the water column when the typhoon stirred the sediments, seems to have little effects on COD increase.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.10
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• pp.591-598
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• 2017

Power overshoot phenomenon was observed in microbial fuel cells (MFCs) used non-catalyzed graphite felt as cathode. Voltage loss in MFCs was mainly caused by cathode potential loss. Cheap stainless steel scrubber, which has high conductivity, and Pt/C coated graphite felt as cathode were used for overcoming power overshoot and reducing the cathode potential loss in MFCs. The MFCs used stainless steel scrubber showed no power overshoot even slow catholyte flow rate and produced 29% enhanced maximum current density ($23.9A/m^3$) than MFCs used non-catalyzed graphite felt while the power overshoot phenomenon was existed in Pt/C coated MFCs. Increasing catholyte flow rate resulted in disappearing power overshoot of MFCs used non-catalyzed graphite felt. In addition, maximum power density and current density of both MFCs used non-catalyzed graphite felt and stainless steel scrubber increased by 2-3.5 times. Cathode potential losses in all region of activation loss, ohmic loss, and mass transport loss were reduced according to increase of catholyte flow rate. Therefore, stainless steel scrubber has advantages that are economical materials as electrode and prevents power overshoot, leading to enhance electricity generation. In addition, increasing catholyte flux is one of great solution when power overshoot caused by cathodic overpotential is observed in MFCs.

• Korean Journal of Environmental Biology
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• v.30 no.4
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• pp.355-361
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• 2012

Genus of Gambierdiscus, Ostrepsis, Prorocentrum, Coolia and Amphidinium are epiphytic ciguatoxin-producing armored dinoflagellate, often attached on macroalgae. These organisms are the primary causative agent of ciguatera fish poisoning which occurs in tropical and subtropical regions. However, regardless of the fact that population of epiphytic dinoflagellates have expanded to such temperate areas from sub-trophic and trophic areas, monitoring of the epiphytic dinoflagellates was greatly lacked in coastal water of Korean Peninsula. This study was performed in the Korean Peninsula in November, 2011. Cell densities of Gambierdiscus spp. on macroalgae ranged from zero to 10 cells $g^{-1}$ and the maximum density was recorded at St.18 (Pohang guryongpo). The abundance of Ostreopsis spp. was highest on macro-algaes Chondrus ocellatus, Lomentaria catenata and Plocamium telfairiae (140 cells $g^{-1}$). The maximum abundance of Prorocentrum, Coolia and Amphidinium were 52, 3 and 1 cells $g^{-1}$, respectively. Of these, Prorocentrum lima was observed at most stations of East Sea. Therefore, our results suggest that the epiphytic armored dinoflagellates may have adapted to Korean coastal water of temperate areas (i.e., East Sea) and those abundances may be related to the macroalgal species.

• Korean Journal of Microbiology
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• v.40 no.4
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• pp.263-268
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• 2004

Two species of halophilic bacteria were isolated from five salted seafoods and identified by 16S rDNA sequenc­ing homology. One was identified as Halomonas subglaciescola and other four strains were belong to Halomo­nas marina. The identity of all isolates with standard organisms was above $95\%.$ H. subglaciescola, H. marina IN, and H. marina SH-2 grew in salinity condition from $3%\;to\;18\%$ NaCl but growth of H. marina SQ and H. marina SH-l grew in salinity environment from $8\%\;to\;17\%.$ Maximum biomass of H. subglaciescola, H. marina IN, H. marina SQ, H. marina SH-1, and H. marina SH-2 growing in LB medium containing $15\%$ NaCl were about 3.2, 4.5, 4.5, 5.7, and 4.2, however the maximum biomass in LB medium containing $5\%$ NaCl were about 2.2, 1.1, 0.7, 0.2, and 2.4 as optical density at 660 nm, respectively. In scanning electron micrograph, unknown material (mucus) attached to outer membrane of all isolates was observed. When mucus isolated from halophilic bacterial cell was added to culture of E. coli, E. coli grew in medium containing $15\%$ NaCl.

• Journal of Sensor Science and Technology
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• v.7 no.2
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• pp.131-139
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• 1998

$CdS_{0.67}Se_{0.33}$ single crystal was grown by vertical sublimation method of closed tube physical vapour deposition. The (0001) growth plane of oriented single crystals was confirmed from the back-ref1ection Laue patterns. From the Hall effects by van der Pauw method, the as-grown $CdS_{0.67}Se_{0.33}$ single crystals were found to be n-type semiconductors. The mobility appeared to be decreased by lattice scattering at temperature range from 150K to 293K and by impurity scattering at temperatures ranging from 30K to 150K In order to explore its applicability in photoconductive cells, we measured the ratio of photo-current to dark-current (pc/dc), maximum allowable power dissipation (MAPD), spectral response and response time respectively. The results indicated that for the samples annealed in Cu vapour the photoconductive characteristics are best. We obtained sensitivity of 0.99, the value of pc/de of $1.84{\times}10^{7}$, the MAPD of 323mW and the rise and decay time of 9.3 ms and 9.7 ms, respectively.

• Microbiology and Biotechnology Letters
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• v.43 no.4
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• pp.314-321
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• 2015

Agar-hydrolyzing bacteria were isolated from the coastal sea water of Jeju Island. One isolate, designated as S4, was selected for further study. The S4 cells were Gram-negative and rod-shaped with smooth beige surfaces and single polar flagellum. Cells were grown at $15-42^{\circ}C$, 0.5-5% (w/v) NaCl, between pH 6.0 and 9.0, and in media containing 0.5-5% (w/v) NaCl. The G+C content was 49.93 mol%. The major fatty acids (>15%) were $C_{18:1}{\omega}7c$, $C_{16:0}$ and Summed feature 3 (comprising $C_{16:1}{\omega}7c/iso-C_{15:0}$ 2-OH). Based on 16S rRNA sequencing and biochemical and chemotaxonomic characteristics, the strain was designated as Vibrio sp. S4. In liquid culture supplemented with 0.1% agar the cell density and agarase activity reached a maximum level in 72 h, while agarase activity in the culture without agar was negligible, implying agarose expression is induced by agar. The optimum pH and temperature for the extracellular crude agarase of S4 were 7.0 and $45^{\circ}C$, respectively. However, it also exhibited 98.6% and 87.6% at $40^{\circ}C$ and $50^{\circ}C$, respectively, of the maximum activity seen at $45^{\circ}C$. The crude agarase hydrolyzed agarose into (neo)agarotetraose and (neo)agarohexaose.

• Polymer(Korea)
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• v.34 no.6
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• pp.540-546
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• 2010

In this manuscript, in order to reduce methanol permeability and, at the same time, to increase proton conductivity THS-PSA containing silica compound, responsible for methanol permeability reduction, and sulfonic acid, responsible for proton conductivity enhancement, was applied onto PVA/PSSA-MA membranes. And in order to improve durability, the resulting membranes, PVA/PSSAMA/THS-PSA, were exposed to 500ppm F2 gas at varying reaction times. The surface-fluorinated membranes were characterized through the measurement of contact angles, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy to observe the physico-chemical changes. For the evaluation of the electro-chemical changes in the resulting membranes, its water contents, ion exchange capacity, proton conductivity, and methanol permeability were measured and then compared with the commercial membrane, Nafion 115. Finally, the membran electrode assembly(MEA) was prepared and the cell voltage against the current density was measured. As fluorination time increased, the contents of F2 increased up to maximum 4.3% and to depth of 50 nm. At 60 min of fluorination, the proton conductivity was 0.036 S/cm, larger than Nafion 115 at 0.024 S/cm, and the methanol permeability was $9.26E-08cm^2/s$, less than Nafion 115 at $1.17E-06cm^2/s$.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.45.1-45.1
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• 2011

Cobalt-free $La_xSr_{4-x}Fe_6O_{13}$ ($0{\leq}x{\leq}2$) oxide have been synthesized and investigated as a potential cathode material for solid oxide fuel cells (SOFCs). $Sr_4Fe_6O_{13}$ consists of alternating perovskite layers ($Sr_4Fe_2O_8$) containing iron cations in octahedral oxygen coordination and $Fe_4O_5$ layers where iron cations have 5-fold coordination of two types-square pyramids and trigonal bipyramids. Our preliminary electrochemical testes of pristine $Sr_4Fe_6O_{13}$ show a rather high area specific resistance ($0.47{\Omega}cm^2$ at $700^{\circ}C$) for ~20 ${\mu}m$ thick layers with CGO electrolyte. The electrochemical performances are improved by La addition up to x=1 ($La_1Sr_3Fe_6O_{13}$, $0.06{\Omega}cm^2$ at $700^{\circ}C$). In addition, thermal expansion coefficient (TEC) values of $La_1Sr_3Fe_6O_{13}$ specimen demonstrated $15.1{\times}10^{-6}\;^{\circ}C^{-1}$ in the range of 25-900$^{\circ}C$, which provides good thermal expansion compatibility with the CGO electrolyte. An electrolyte supported (300-${\mu}m$-thick) single-cell configuration of $La_1Sr_3Fe_6O_{13}$/CGO/Ni-CGO delivered a maximum power density of 584 $mWcm^{-2}$ at $700^{\circ}C$. In addition, an anode supported single cell by YSZ electrolyte (10-${\mu}m$-thick) with a porous CGO interlayer between the cathode and the electrolyte to avoid undesired interfacial reactions exhibited 1,517 $mWcm^{-2}$ at $800^{\circ}C$. The unique composition of $La_1Sr_3Fe_6O_{13}$ with low thermal expansion coefficient and higher electrochemical properties could be a good cathode candidate for intermediate temperature SOFCs with CGO and YSZ electrolyte.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.63-67
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• 2010

The organic solar cells with Glass/ITO/PEDOT:PSS/P3HT:PCBM/Al structure were fabricated using regioregular poly (3-hexylthiophene) (P3HT) polymer:(6,6)- phenyl $C_{61}$-butyric acid methyl ester (PCBM) fullerene polymer as the bulk hetero-junction layer. The P3HT and PCBM as the electron donor and acceptor materials were spin casted on the indium tin oxide (ITO) coated glass substrates. The optimum mixing concentration ratio of photovoltaic layer was found to be P3HT:PCBM = 4:4 in wt%, indicating that the short circuit current density ($J_{SC}$), open circuit voltage ($V_{OC}$), fill factor (FF) and power conversion efficiency (PCE) values were about 4.7 $mA/cm^2$, 0.48 V, 43.1% and 0.97%, respectively. To investigate the effects of the post annealing treatment, as prepared organic solar cells were post annealed at the treatment time range from 5min to 20min at $150^{\circ}C$. $J_{SC}$ and $V_{OC}$ increased with increasing the post annealing time from 5min to 15min, which may be originated from the improvement of the light absorption coefficient of P3HT and improved ohmic contact between photo voltaic layer and Al electrode. The maximum $J_{SC},\;V_{OC}$, FF and PCE values of organic solar cell, which was post annealed for 15min at $150^{\circ}C$, were found to be about 7.8 $mA/cm^2$, 0.55 V, 47% and 2.0%, respectively.