Papers by Author: Soo Jin Park

Abstract: In this work, nickel (Ni)-loaded activated carbon nanotubes (ACNTs) were prepared for hydrogen storage applications. The process was conducted by chemical activation method at 900oC with KOH:CNTs ratios (4:1, g/g). And then, Ni-loaded ACNTs were also formulated to investigate the hydrogen storage characteristics as a function of Ni content. The microstructures of the Ni-loaded ACNTs were characterized by XRD and TEM measurements. The textural properties of the samples were analyzed using N2 adsorption isotherms at 77 K. The BET, D-R, and BJH equations were used to observe the specific surface areas, the micropore, and mesopore structures, respectively. The hydrogen storage capacity of the Ni-loaded ACNTs was measured at 298 K at a pressure of 100 bar. It was found that the hydrogen storage capacity of Ni-loaded ACNTs was enhanced in proportion to the Ni content, with Ni-5-ACNTs exhibiting the largest hydrogen storage capacity. Therefore, it could be concluded that the significantly created micropores on CNTs by chemical activation had an effect on hydrogen storage behaviors as well as the Ni particles played an important role in hydrogen storage characteristics due to the hydrogen spillover effect.

Abstract: Recently core/shell nanostructures including nanotubes, nanowires, and nanofibers have a considerable attension because multiple or enhanced functionality can be obtained by the synergistic effect of different materials in the formation of a core/shell structure. In this work, porous carbon/carbon core/shell carbon electrode (P-C/C-CE) composed of core graphene and disordered shells were prepared to obtain a new type of carbon electrode materials. The disordered carbon shells were prepared by coating of polyaniline onto the graphene by in-situ polymerization in the presence of nano-sized silica and subsequent carbonization at 850°C. After carbonization, P-C/C-CE showed the hollow structure and crystallinity. In addition, P-C/C-CE exhibited superior electrochemical performance compared to graphene and graphene/PANI composites, which was attributed to the high surface area of P-C/C-CE and the presence of nitrogen groups formed onto carbon electrode after the carbonization of shell polyaniline.

Abstract: In this work, poly(amide imide) (PAI) fibers containing various silicon content ratios were prepared for the precursor of carbon fibers by electrospinning method from 25 wt.% PAI in dimethylformamide (DMF) solution. The fibers were stabilized and then subsequently carbonized in a flow of nitrogen to obtain porous Si/carbon fibers. The morphologies and the crystalline structures of the Si/CFs were characterized by scanning electron microscopy (SEM) and X-ray diffractometer (XRD). The electrochemical behaviors of the Si/CFs were observed by cyclic voltammetry tests. The experimental results indicated that the Si/CFs exhibited convoluted structure and wrinkled surface morphology. The silicon particles had a uniform diameter of approximately 1 μm. And the electrochemical activity of the Si/CFs was gradually improved due to the buffering effect of the large Si volume expansion and shrinkage. In addition, the fibers exhibited large accessible surface area, high reversible capacity, and relatively good cycling performance at high current densities. Consequently, it was found that the introduction of silica could affect the electrochemical properties of the CFs, and the Si/CFs might have potential applications for various fields of electrochemical materials.

Abstract: In this work, we synthesized graphene nanosheets via a soft chemistry synthetic route involving pre-exfoliation treatment, strong oxidation, and post thermal exfoliation. X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) confirmed the ordered graphite crystal structure and morphology of graphene nanosheets. N2 adsorption was used to determine the specific surface area of graphene nanosheets. As a result, pre-treatment of the graphite with HNO3/H2SO4 mixture produced the exfoliated graphite nanoplates, and the post thermal exfoliation of the graphite oxide nanosheets at low temperature led to produce a large number graphene nanosheets. The specific surface area of obtained graphene nanosheets was 333 m2/g.

Abstract: In this work, carbon nanofibers(CNFs) were prepared by using electrospinning method. Phosphoric acid and sodium carbonate activation of CNFs were conducted to increase surface area and pore volume. Pore structures of activated CNFs were developed with increasing surface area and pore volume through activation. Specific surface area increased about 60 times and total pore volume developed around 120 times. Activated CNFs have different pore distribution with different chemical agent.

Abstract: In this work, nano-sized nickel particles were dispersed on multi-walled carbon nanotubes using multi-step impregnation method, to use them as hydrogen storage media. The dispersion degree of nickel particles on multi-walled carbon nanotubes is inversely proportional to the nickel concentration of solution. It was observed that the low nickel concentration is efficient to decorate nickel particles into the inner space. Multi-step impregnation method of MWNTs through several times with low nickel concentration is more efficient to manufacture Ni-MWNTs having well dispersed metallic nickel particles.

Abstract: The rheological behaviors of mesophase pitch containing different contents (0, 1.0, 2.0 wt%) of multi-wall carbon nanotubes (MWNTs) were studied by using ARES cone-plate rheometer. The dynamic response of mesophase pitch containing MWNTs was different from that of pure mesophase pitch due to the MWNTs as a suspension in viscous pitch. The dynamic viscosity increased with increasing the amount of MWNTs, which is a clear evidence of the interruption of MWNTs in mesophase pitch. Also, the phase angle result indicates that mesophase pitch containing MWNT had less elastic nature than pure mesophase pitch.

Abstract: In this work, the thermal and mechanical interfacial properties of diglycidylether of bisphenol A (DGEBA)/polyurethane modified epoxy (UME-305) blends were investigated. 4,4’-Diaminodiphenyl methane (DDM) was used as a curing agent, and the content of UME-305 in the mixture was 0, 20, 40, 60, 80, and 100 wt%. The cure behaviors of DGEBA/UME-305 blends were studied by DSC. The mechanical interfacial properties were confirmed by critical stress intensity factor (KIC) at 77K and 298K. As a result, the exothermic peaks in DSC results were shifted to higher temperature region as increasing the UME-305 content in the blends. The KIC was also enhanced with increasing the UME-305 content and showing a maximum value at 60 wt.% UME-305.

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.