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Lim, Dongwook,Park, Taesoon,Choi, Yeji,Oh, Euntaek,Shim, Snag Eun,Baeck, Sung-Hyeon The Korean Electrochemical Society 2020 Journal of electrochemical science and technology Vol.11 No.2
Highly ordered mesoporous manganese oxide films were electrodeposited onto indium tin oxide coated (ITO) glass using sodium dodecyl sulfate (SDS) and ethylene glycol (EG) which were used as a templating agent and stabilizer for the formation of micelle, respectively. The manganese oxide films synthesized with surfactant templating exhibited a highly mesoporous structure with a long-range order, which was confirmed by SAXRD and TEM analysis. The unique porous structure offers a more favorable diffusion pathway for electrolyte transportation and excellent ionic conductivity. Among the synthesized samples, Mn<sub>2</sub>O<sub>3</sub>-SDS+EG exhibited the best electrochemical performance for a supercapacitor in the wide range of scan rate, which was attributed to the well-developed mesoporous structure. The Mn<sub>2</sub>O<sub>3</sub> prepared with SDS and EG displayed an outstanding capacitance of 72.04 F g<sup>-1</sup>, which outperform non-porous Mn<sub>2</sub>O<sub>3</sub> (32.13 F g<sup>-1</sup>) at a scan rate of 10 mV s<sup>-1</sup>.
Lim, Dongwook,Lee, Young-Wook,Pasquato, Mario,Han, Sang-Il,Roh, Dong-Goo American Astronomical Society 2016 The Astrophysical journal Vol.832 No.2
<P>Most globular clusters (GCs) are now known to host multiple stellar populations with different abundances of light elements. Here we use narrow-band photometry and low-resolution spectroscopy for NGC. 362 and NGC. 6723 to investigate their chemical properties and radial distributions of subpopulations. We confirm that NGC. 362 and NGC. 6723 are among the GCs with multiple populations showing bimodal CN distribution and CN-CH anticorrelation without a significant spread in calcium abundance. These two GCs show more centrally concentrated CN-weak, earlier generation stars compared to the CN-strong, later generation stars. These trends are reversed with respect to those found in previous studies for many other GCs. Our findings, therefore, seem contradictory to the current scenario for the formation of multiple stellar populations, but mass segregation acting on the two subpopulations might be a possible solution to explain this reversed radial trend.</P>
Bimetallic NiFe alloys as highly efficient electrocatalysts for the oxygen evolution reaction
Lim, Dongwook,Oh, Euntaek,Lim, Chaewon,Shim, Sang Eun,Baeck, Sung-Hyeon Elsevier 2020 CATALYSIS TODAY - Vol.352 No.-
<P><B>Abstract</B></P> <P>In this study, binary NiFe alloy nanoparticles are successfully prepared using a simple hydrothermal method followed by H<SUB>2</SUB> reduction. The nanoparticles are then applied as electrocatalysts for oxygen evolution reaction (OER). Compared to unary Ni or Fe, the binary NiFe alloy electrocatalyst exhibits a much lower overpotential of 298 mV at a current density of 10 mA cm<SUP>−2</SUP>, and it exhibits electrocatalytic activity for OER superior to that of state-of-the-art RuO<SUB>2</SUB> and IrO<SUB>2</SUB> noble metal oxide catalysts. Moreover, the alloy catalyst exhibits substantial long-term durability after 1000 cyclic voltammetry tests. This remarkable electrochemical performance mainly originates from the synergistic effects of Fe incorporation into Ni species, leading to the improved charge transfer kinetics and intrinsic activity of the catalyst. These results provide a promising avenue for developing cost-effective and high-performance electrocatalysts as advanced electrodes for energy storage and conversion systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bimetallic Fe<SUB>0.64</SUB>Ni<SUB>0.36</SUB> Alloys were prepared by a hydrothermal method followed by mild H<SUB>2</SUB> reduction. </LI> <LI> The binary metal alloys exhibited a low overpotential and substantial long-term stability for oxygen evolution reaction. </LI> <LI> This outstanding OER performance and durability can be attributed to the synergistic effect of binary metal. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
LOW-RESOLUTION SPECTROSCOPIC STUDIES OF GLOBULAR CLUSTERS WITH MULTIPLE POPULATIONS
LIM, DONGWOOK,HAN, SANG-IL,ROH, DONG-GOO,LEE, YOUNG-WOOK The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
Recent narrow-band Ca photometry discovered two distinct red giant branch (RGB) populations in some massive globular clusters (GCs) including M22, NGC 1851, and NGC 288. In order to investigate the differences in light/heavy elements abundances between the two subpopulations, we have performed low-resolution spectroscopy for stars on the two RGBs in these GCs. We find a significant difference (more than $4{\sigma}$) in calcium abundance from the spectroscopic HK' index for both M22 and NGC 1851. We also find a more than $8{\sigma}$ difference in CN band strength between the Ca-strong and Ca-weak subpopulations. For NGC 288, however, we detect the presence of a large difference only in the CN strength. The calcium abundances of the two subpopulations in this GC are identical within errors. We also find interesting differences in CN-CH relations among these GCs. While CN and CH indices are correlated in M22, they show an anti-correlation in NGC 288. However, NGC 1851 shows no difference in CH between two groups of stars having different CN strengths. The CN bimodality in these GCs could be explained by pollution from intermediate-mass asymptotic giant branch stars and/or fast-rotating massive stars. For the presence or absence of calcium bimodality and the differences in CN-CH relations, we suggest these would be best explained by how strongly type II supernovae enrichment has contributed to the chemical evolutions of these GCs.