Mechanical strength improvement of aluminum foam-reinforced matrix for molten carbonate fuel cells

Lee, Mihui,Lee, Chang-Whan,Ham, Hyung-Chul,Han, Jonghee,Yoon, Sung Pil,Lee, Ki Bong Elsevier 2017 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.42 No.25

<P><B>Abstract</B></P> <P>During the cell operation of molten carbonate fuel cells (MCFCs), matrix cracks caused by poor mechanical strength accelerate cell performance degradation. Therefore, for a stable long-term cell operation, the improvement of mechanical properties of matrix is highly required. In this study, aluminum foam was used to enhance the mechanical strength of the matrix as a 3D (three dimensional) support structure. Unlikely conventional matrix (pure α-LiAlO<SUB>2</SUB> matrix) which has paste-like structure at the MCFC operating temperature, Al foam-reinforced α-LiAlO<SUB>2</SUB> matrix has significantly strong mechanical strength because the 3D network structure of Al foam can form the harden alumina skin layer during a cell operation. As a result, the mechanical strength of the Al foam-reinforced α-LiAlO<SUB>2</SUB> matrix was enhanced by 9 times higher than the pure α-LiAlO<SUB>2</SUB> matrix in a 3-point bending test. In addition, thermal cycle test showed notable cell stability due to strong mechanical strength of Al foam-reinforced α-LiAlO<SUB>2</SUB> matrix. The Al foam-reinforced α-LiAlO<SUB>2</SUB> matrix shows appropriate microstructure to preserve the liquid electrolyte when performing the mercury porosimeter analysis and differential pressure test between anode and cathode. Moreover, evaluation of stability and durability for a long-term cell operation were demonstrated by single cell test for 1,000 h.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Matrix had reinforced by 3 dimensional structure of Al foam with Al<SUB>2</SUB>O<SUB>3</SUB> surface layer. </LI> <LI> Reinforced α-LiAlO<SUB>2</SUB> matrix showed higher bending strength than pure α-LiAlO<SUB>2</SUB> matrix. </LI> <LI> Reinforced α-LiAlO<SUB>2</SUB> matrix stayed stable even after 13 times of thermal cycling test. </LI> </UL> </P>

Clinical characteristics and mortality risk factors among trauma patients by age groups at a single center in Korea over 7 years: a retrospective study

( Jonghee Han ),( Su Young Yoon ),( Junepill Seok ),( Jin Young Lee ),( Jin Suk Lee ),( Jin Bong Ye ),( Younghoon Sul ),( Seheon Kim ),( Hong Rye Kim ) 대한외상학회 2023 大韓外傷學會誌 Vol.36 No.4

Purpose: In this study, we aimed to compare the characteristics of patients with trauma by age group in a single center in Korea to identify the clinical characteristics and analyze the risk factors affecting mortality. Methods: Patients aged ≥18 years who visited the Chungbuk National University Hospital Regional Trauma Center between January 2016 and December 2022 were included. The accident mechanism, severity of the injury, and outcomes were compared by classifying the patients into group A (18-64 years), group B (65-79 years), and group C (≥80 years). In addition, logistic regression analysis was performed to identify factors affecting death. Results: The most common injury mechanism was traffic accidents in group A (40.9%) and slipping in group B (37.0%) and group C (56.2%). Although group A had the highest intensive care unit admission rate (38.0%), group C had the highest mortality rate (9.5%). In the regression analysis, 3 to 8 points on the Glasgow Coma Scale had the highest odds ratio for mortality, and red blood cell transfusion within 24 hours, intensive care unit admission, age, and Injury Severity Score were the predictors of death. Conclusions: For patients with trauma, the mechanism, injured body region, and severity of injury differed among the age groups. The high mortality rate of elderly patients suggests the need for different treatment approaches for trauma patients according to age. Identifying factors affecting clinical patterns and mortality according to age groups can help improve the prognosis of trauma patients in the future.

Highly efficient green, blue, and white phosphorescent inverted organic light-emitting diodes by improving charge injection and balance

Lee, Hyunkoo,Maeng, Min-Jae,Hong, Jong-Am,Najnin, Rokeya,Moon, Jaehyun,Cho, Hyunsu,Lee, Jonghee,Yu, Byoung-Gon,Park, Yongsup,Cho, Nam Sung The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.38

<▼1><P>Highly efficient green, blue, and white phosphorescent inverted organic light-emitting diodes were demonstrated by improving charge injection and balance.</P></▼1><▼2><P>To improve the performance of inverted organic light-emitting diodes (OLEDs), we investigated the electrical, optical, and interfacial properties of three different lithium (Li)-doped electron transport materials (ETMs): tris(3-(3pyridyl)mesityl)borane (3TPYMB), 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), and 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB). The electron injection barriers (EIBs) between indium-tin-oxide and the ETMs were deduced for both pristine and Li-doped cases from ultraviolet photoelectron spectroscopy measurements and optical band gap values. The Li-doped ETMs showed EIB values of approximately 0.03 eV, 0.77 eV, and 0.81 eV for 3TPYMB, TmPyPB, and BmPyPB, respectively, which are much lower than those of their pristine counterparts of 0.94 eV, 1.14 eV, and 1.48 eV, respectively. The Li-doped ETMs were employed as electron injection layers (EILs) of inverted bottom-emission OLEDs (IBE-OLEDs) with green phosphorescence. IBE-OLEDs with 3TPYMB, TmPyPB, and BmPyPB EILs exhibited driving voltages of 3.6 V, 4.0 V, and 4.5 V at 1000 cd m<SUP>−2</SUP> and maximum external quantum efficiencies (EQEs) of 20.3%, 19.7%, and 16.5%, respectively. From the low EIB of Li-doped 3TPYMB, we also demonstrated highly efficient blue and white phosphorescent IBE-OLEDs. We optimized the device structure to improve the charge balance and out-coupling efficiency by changing the hole injection layer and the thickness of the hole and electron transport layers with optical simulation. The blue device showed a maximum EQE and luminous current efficiency of 22.9% and 43.1 cd A<SUP>−1</SUP>, respectively. In addition, the white device exhibited a high EQE and luminous efficacy of 19.3% and 37.8 lm W<SUP>−1</SUP> at 3 mA cm<SUP>−2</SUP> (∼1000 cd m<SUP>−2</SUP>), respectively. To the best of our knowledge, the efficiencies of these green, blue, and white devices are the highest values obtained to date with a low driving voltage for IBE-OLEDs without any additional light-extraction structure. Since the Li-doped 3TPYMB has an extremely low EIB and shows good device performance, it can be utilized as an effective EIL in inverted-structure devices.</P></▼2>

Fabrication of Three-Dimensional Single-Walled Carbon Nanotube Networks Suspended on Si Pillar Architecture

Lee, Jongtaek,Lee, Junyoung,Yang, Jonghee,Park, Taehun,Ahn, Sang Jung,Yi, Whikun American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.8

<P>We synthesized three-dimensional (3-D) SWNT networks suspended on Si pillar architecture. The pillar arrays on Si substrate were formed by a standard photolithography technique using a patterned chrome mask and plasma etching in a SF6:C4F8 gas mixture. Successively, 3-D SWNT networks were synthesized between pillar arrays by a thermal chemical vapor deposition. We investigated the optical properties and formation of 3-D SWNT networks suspended on Si pillar arrays through controlling catalyst deposition methods between pillar arrays by using scanning electron microscopy and Raman spectroscopy. We confirmed that the bridging and connecting of SWNTs between Si pillars, suggesting the effective growth of the 3-D SWNT networks on Si pillar architecture for application to large scale and well-organized devices.</P>

A Light Scattering Layer for Internal Light Extraction of Organic Light-Emitting Diodes Based on Silver Nanowires

Lee, Keunsoo,Shin, Jin-Wook,Park, Jun-Hwan,Lee, Jonghee,Joo, Chul Woong,Lee, Jeong-Ik,Cho, Doo-Hee,Lim, Jong Tae,Oh, Min-Cheol,Ju, Byeong-Kwon,Moon, Jaehyun American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.27

<P>We propose and fabricate a random light scattering layer for light extraction in organic light-emitting diodes (OLEDs) with silver nanodots, which were obtained by melting silver nanowires. The OLED with the light scattering layer as an internal light extraction structure was enhanced by 49.1% for the integrated external quantum efficiency (EQE). When a wrinkle structure is simultaneously used for an external light extraction structure, the total enhancement of the integrated EQE was 65.3%. The EQE is maximized to 65.3% at a current level of 2.0 mA/cm(2). By applying an internal light scattering layer and wrinkle structure to an OLED, the variance in the emission spectra was negligible over a broad viewing angle. Power mode analyses with finite difference time domain (FDTD) simulations revealed that the use of a scattering layer effectively reduced the waveguiding mode while introducing non-negligible absorption. Our method offers an effective yet simple approach to achieve both efficiency enhancement and spectral stability for a wide range of OLED applications.</P>

High performance ITO-free white organic light-emitting diodes using highly conductive PEDOT:PSS transparent electrodes

Lee, Jonghee,Kim, Yong Hyun Elsevier 2018 Synthetic metals Vol.242 No.-

<P><B>Abstract</B></P> <P>We report high performance white organic light-emitting diodes (OLEDs) based on high conductivity poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films optimized by a solvent post treatment. The device stack is carefully optimized with high efficiency tandem structures including red, yellow/green, and blue emissive materials. The OLED with the PEDOT:PSS transparent electrode achieves a high power efficiency of 26.1 lm/W and an external quantum efficiency of 19.3%, which are comparable to the reference indium tin oxide (ITO)-based OLEDs. In addition, it is observed that the angular emission characteristic of PEDOT:PSS-based OLEDs is closer to Lambertian distribution compared to that of the ITO-based OLED. We show that the optimized device stack together with post-treated PEDOT:PSS transparent electrodes can realize high performance ITO-free white OLEDs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Efficient ITO-free white OLEDs prepared with conductive polymers are presented. </LI> <LI> The device efficiency is boosted by using the optimized tandem structure. </LI> <LI> The optimized device stack results in the high efficiency of ITO-free white OLEDs. </LI> </UL> </P>

Polymer Quantum Dot-Sensitized Solar Cell Incorporating Single-Walled Carbon Nanotubes

Lee, Junyoung,Lee, Jongtaek,Yang, Jonghee,Park, Taehun,Ahn, Sang Jung,Yi, Whikun American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.8

<P>Regioregular poly(3-hexylthiophene) (P3HT) of conjugated polymer is known to be p-type hole transports material. P3HT is used as a material to substitute for the liquid electrolyte in the quantum dot-sensitized solar cells (QDSSCs). In order to gain high performance of the cell, three different cells using P3HT, pristine P3HT, single-walled carbon nanotube (SWNT)-mixed P3HT (mixing), and SWNT-blended P3HT (blended) are made and their photovoltaic cells measure J-V curve, incident photon to current efficiency, and electrochemical impedance spectroscopy. Those values obtained from experiments are compared with each other.</P>

Improvements of phosphorescent white OLEDs performance for lighting application.

Lee, Jonghee,Chu, Hye Yong,Lee, Jeong-Ik,Song, Ki-Im,Lee, Su Jin American Scientific Publishers 2008 Journal of Nanoscience and Nanotechnology Vol.8 No.10

<P>We developed white OLED device with high power efficiency, in which blue and orange phosphorescent emitters were used. By introduction of multi-functional interlayer which has partial doping of orange dopant inside EBL, we report WOLEDs with peak external efficiencies up to (14.1% EQE, 31.3 Im/W) without light out-coupling technique. At 1000 cd/m2, the performance achieved was 11.9% EQE, 18.7 Im/W with CIE = (0.39, 0.44). We also found that WOLED performances are related with doping ratio of the orange dopant that was inserted inside EBL.</P>

Study on the effect of current collector structures on the performance of MCFCs using three-dimensional fluid dynamics analysis

Lee, Chang-Whan,Lee, Mihui,Yoon, Sung-Pil,Ham, Hyung-Chul,Choi, Sun Hee,Han, Jonghee,Nam, Suk Woo,Yang, Dong-Yol Elsevier 2017 Journal of industrial and engineering chemistry Vol.51 No.-

<P><B>Abstract</B></P> <P>The effect of current collectors of molten carbonate fuel cells (MCFCs) was studied through three-dimensional computational fluid dynamics and experiments. Three types of current collectors such as a sheet with sheared protrusions and perforated sheets were employed and performances of MCFCs were compared. A current collector structure with a large gas open area to electrodes improves diffusion characteristics between electrodes and gas flow channels. As a result, differences of gas mole fractions between gas flow channels and electrodes were decreased. Finally, Nernst loss and cathode polarization loss decreased, and the performance was enhanced. Using these results, current collector structures for improved performance and long-term operation were discussed.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Improved performance of molten carbonate fuel cells with (Li/Na)₂CO₃ electrolytes by using BYS coated cathode at low operating temperatures

Lee, Chang-Whan,Kwon, Byeong Wan,Kang, Min-Goo,Ham, Hyung-Chul,Yoon, Sung-Pil,Han, Jonghee,Kim, Young Jin,Lee, Min Chul Elsevier 2017 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.42 No.29

<P><B>Abstract</B></P> <P>In order to improve the stack life time of MCFCs, it is necessary to reduce the operating temperature of MCFCs below 600 °C, because reduced operating temperature minimizes electrolyte loss due to evaporation and corrosion. However, at the low operating temperature below 600 °C, the cell performance of MCFCs with (Li/Na)<SUB>2</SUB>CO<SUB>3</SUB> electrolyte is too low to operate the fuel cell stack and system. In this study, we have performed wettability control of the liquid molten carbonate electrolyte by coating NiO cathodes with poor wetting property of the mixed ionic and electronic conductor (MIEC) such as BYS (Bi<SUB>1.5</SUB>Y<SUB>0.3</SUB>Sm<SUB>0.3</SUB>O<SUB>3-δ</SUB>). From experiments with symmetrical cells, each polarization component with various temperatures and gas conditions were studied. To investigate effects of the BYS coated cathode on the performance of MCFCs, a 100 cm<SUP>2</SUP> single cell of MCFCs was employed. The performance of a 100 cm<SUP>2</SUP> single cell with BYS coated cathode was better than that with conventional cathode by a factor of 1.84, because BYS coated cathode reduces activation polarization and mass transfer resistance greatly.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Wettability of NiO cathodes was controlled by coating BYS powders. </LI> <LI> Effects of the BYS coated cathode on the performance of MCFCs were investigated. </LI> <LI> BYS coated cathode reduces polarizations and mass transfer resistance. </LI> </UL> </P>