Papers by Author: Seok Kim

Abstract: Electroactivity of graphite nanofibers (GNFs)-supported PtRu particles was examined for their application as DMFCs anode. In this work, composites of PtRu nanoparticles of 2-8 nm size and graphite nanofibers were prepared by the electrodeposition methods. As a result, the methanol oxidation current for graphite nanofibers-supported PtRu catalysts was investigated by changing a deposition time. The electroactivity could be attributed to the particle size, particle dispersion ability, and deposition level.

Abstract: Graphite nanofibers (GNFs)–supported platinum (Pt) catalysts had been prepared by an electrochemical deposition by controlling an applied potential to a potential of Pt reduction. Pt nanoparticles were successfully deposited by using potential sweep methods. The catalyst prepared by 18 sweep times showed the lowest resistance and the highest electroactivity. These electrochemical properties were dependent on the size, loading level, and morphology of catalysts. The influences of electrochemical condition on the sizes and loading level of catalysts were also investigated.

Abstract: We present the adsorption characteristics of uranyl ions on a new and innovative composite which was composed of a carboxymethylated polyethyleneimine (CM-PEI) and an activated carbon (F400) with a nanopore less than 2 nm in diameter. In this study, we examined the adsorption phenomena of uranyl ions on the CM-PEI/F400 composite and evaluated the adsorption data using various isotherm models. It was found that the adsorption of uranyl ions on the CM-PEI/F400 composite obeys the Langmuir isotherm model. In addition, it was observed that pH of solutions had great influence on the adsorption capacity of uranyl ions on the CM-PEI/F400 composite. Specially, the adsorption capacity of uranyl ions was linearly increased with an increase of pH at pH > 3.0.

Abstract: In this study, we modified the surface of nanoporous carbons with carboxymethylated polyethyleneimine (CM-PEI) of a high charge density in order to increase the Pt loading on the nanoporous carbons in an aqueous solution. We carried out equilibrium adsorption tests of Pt(IV) on the pure nanoporous carbon and the CM-PEI-coated carbons and evaluated the adsorption isotherm on the CM-PEI-coated carbon using various isotherm models. It was found that the adsorption of Pt(IV) onto the CM-PEI-coated carbons obeys the Langmuir isotherm model.

Abstract: In this work, PtRu/CNTs catalysts were prepared by pulse potential plating methods. The particle size and loading level of catalysts were measured by changing the plating time and pulse interval of pulse potential plating method. Electrochemical activities of PtRu/CNTs catalysts were measured by cyclic voltammetry (CV). PtRu/CNTs catalysts showed an increased the electrochemical activity of methanol oxidation up to 24min and a slightly decreased activity over 24min. The electrochemical activity was increased with increasing of the pulse interval. Consequently, it was found that optimal plating time was 24min and optimal pulse interval was 0.5s for electrochemical activity of PtRu/CNTs catalysts.

Abstract: Multi-walled carbon nanotubes (MWNTs) were oxyfluorinated at several different temperatures. The results indicated that graphitic carbon was the major carbon functional component on the MWNT surfaces and other functional groups, such as C–O, C=O, HO–C=O, C–Fx, were also present after oxyfluorination. The changes of surface properties of oxyfluorinated MWNTs were investigated using FT-IR, EDS and XRD. From the surface analysis, it was found that surface fluorine and oxygen contents increased with increasing oxyfluorination temperature and showed a maximum value at 100 °C. Consequently, it was found that optimal treatment temperature was 100 °C for the best electro activity of Pt/MWNT-100 catalyst and the oxyfluorinated Pt/MWNTs possessed the better electrochemical properties than the pristine Pt/MWNTs.

Abstract: Solid type polymer electrolyte is in progress of research and development in many ways to improve an ionic conductivity to attain 10-3 S/cm which is possibility of practical use of secondary lithium ion battery. There are two major methods of improving ionic conductivity; either lowering Tg of polymer or lowering the energy of ionic movement. In this work, the solid type polymer electrolyte (SPE) composites, which were composed of poly(ethylene oxide) (PEO), ethylene carbonate (EC) as a plasticizer, lithium salt, and 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF6) as a filler in order to improve the ion conductivity of the SPE, were prepared. The influence of EMI-PF6 contents on the ionic conductivity of the SPE composites was investigated in this work. As a result, the ionic conductivity of the SPE was enhanced by an increase in EMI-PF6 content, and showed the highest ionic conductivity at 40 wt.%. It was thought that there was a close correlation between the mobility of Li+ and EMI content in a SPE composite system.

Abstract: Polymeric composite electrolytes (PCE) based on poly(ethylene oxide) (PEO) and mesoporous silicates as a filler material were fabricated, and investigated for understanding the effects of filler addition into the polymer matrix on the ionic conductivity. For a lithium battery application, it is necessary to increase ion conductivity of PCE by modification of microstructure. The ionic conductivity was enhanced with increasing MCM-41 contents due to the decreased crystallinity of PEO. Furthermore, the regular mesoporous structure could be functioned as an ion transfer channel for high ion mobility.

Abstract: In this work, the polymeric electrolyte composites (PECs) based on poly(ethylene oxide) (PEO), ethylene carbonate (EC) as a plasticizer, and lithium montmorillonite (Li-MMT) clay were fabricated, and investigated for understanding the effects of Li-MMT/EC in the polymer matrix on the ionic conductivity. For a lithium battery application, the native sodium cations in MMT were exchanged for lithium cations. As a result, the lithium ion was intercalated into the layer of the MMT clay, and thus PEO entered the galleries of MMT clay. The ionic conductivity was enhanced with increasing MMT contents due to the immobile MMT clay serving as the anion species and the decreased crystallinity of PEO.