Ki Chul Park

High performance of cup-stacked-type carbon nanotubes as a Pt–Ru catalyst support for fuel cell applications

The potential of cup-stacked-type carbon nanotubes (CSCNTs) as a catalyst support for the direct methanol fuel cells has been investigated by the electrochemical oxidation of methanol at various temperatures. The CSCNT-supported platinum–ruthenium (Pt–Ru) bimetallic catalyst exhibited twice as high a power density as the Pt–Ru catalyst supported on Vulcan XC-72 carbon, which is widely used as a catalyst support for the DMFC electrodes. The microscopic analysis of the CSCNT-supported Pt–Ru catalysts revealed that the bimetallic electrocatalysts were well dispersed on the CSCNT supports, and the particle size of the electrocatalysts was ca.5nm . The results of this work indicate that the performance of the carbon support materials is largely influenced by their electrical properties, morphology and crystallographic structures.

High energy-density capacitor based on ammonium salt type ionic liquids and their mixing effect by propylene carbonate

Novel ionic liquids comprised of a quaternary ammonium salt type cation have been applied to an electrolyte for high-performance electric double-layer capacitors (EDLCs). The novel ionic liquids [IL-B; N, N-diethyl-N-methyl(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF 4 ) and IL-T; N, N-diethyl-N-methyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI)] are promising candidates for EDLC electrolytes in terms of high decomposition voltage (wide voltage window), nonflammability, easy handling, nonvolatility, and low production costs. Notably, the wide voltage window indicates that IL-B and IL-T are more advantageous in energy density than typical propylene carbonate-based electrolytes (i.e., TEA-BF 4 /PC) and a conventional imidazolium type ionic liquid (i.e., 1-ethyl-3-methylimidazolium tetrafluoroborate, EMI-BF 4 ). The effectiveness of IL-B and IL-T on the application to EDLC electrolytes has been confirmed by using KOH-activated mesophase pitch-based carbon fibers (MPCFs) as an electrode material. The combination of IL-T (IL-B) and KOH-activated MPCFs has provided 56 F/g (51 F/g) of high specific capacitance at maximum (1 mA/cm 2 discharge current density, 3.5 V charging voltage), which is equivalent to 224 F/g (204 F/g) in a conventional three-compartment measuring system. In addition, the specific capacitance of both ionic liquids has increased proportional to the increase in the applied voltage from 2.5 to 3.5 V, in contrast to the decline observed for TEA-BF 4 /PC at 3.5 V. Furthermore, the mixture of the IL-B exhibiting high viscosity with propylene carbonate (1 M of IL-B in PC) has been found to provide an excellent capacitance behavior comparable to that observed for the pure IL-B. This indicates that the mixture has great potential for application to EDLC electrolytes, similar to pure IL-B and IL-T.

Gasification reaction of organic compounds catalyzed by RuO2 in supercritical water

Nearly complete gasification of organic compounds has been achieved by stoichiometrically insufficient amounts of RuO2 in supercritical water (SCW) to provide CH4, CO2 and H2, all the hydrogen atoms of which originate from water, and the catalytic effect of RuO2 results from a redox couple of Ru(IV)/Ru(II) induced by SCW.

Progressive and invasive functionalization of carbon nanotube sidewalls by diluted nitric acid under supercritical conditions

Distinctive direct sidewall functionalization of multi-wall carbon nanotubes (MWCNTs) has been carried out using dilute nitric acid (HNO3) under supercritical water (SCW) conditions. The functionalization proceeded invasively from the outer to the inner graphitic layers of the MWCNTs as the reaction progressed. The resulting nanotube-derived material was comprised of a functionalized amorphous carbon sheath and the remaining inner nanotube covered with the sheath. The functional groups induced in the sheath region included alcoholic hydroxyl groups, which endowed the nanotube-derived material with hygroscopicity. The reaction pathways for the functional group formation involved hydration and dehydration processes as well as HNO3 oxidation in the SCW medium. The results of this work have demonstrated the effectiveness of the SCW regime on the direct chemical modification of CNT sidewalls.

Carbon-supported Pt–Ru nanoparticles prepared in glyoxylate-reduction system promoting precursor–support interaction

A high dispersion of carbon-supported Pt–Ru alloy nanoparticles have been prepared in an alkaline aqueous solution by using glyoxylate as a reducing agent. The glyoxylate monoanion is converted to oxalate dianion with the reduction of metal precursor ions. The surface-potential analysis of unsupported Pt–Ru black in the presence of all the anion species coexistent in the preparation system suggests a possibility of oxalate dianion as the most effective particle stabilizer. In the glyoxylate-reduction system, a precursor–support interaction is significantly promoted to affect the formation and stabilization of nanoparticles. The glyoxylate reduction at 20-wt% metal loading has provided a higher Pt(0)/Ru concentration ratio in the near-surface region than that of 60-wt% catalyst. The structural and morphological features and advantageous surface composition of the 20-wt% catalyst contribute to the high mass activity for methanol oxidation in the anode overpotential range of typical direct methanol fuel cells.

Edge-enriched, porous carbon-based, high energy density supercapacitors for hybrid electric vehicles.

Supercapacitors can store and deliver energy by a simple charge separation, and thus they could be an attractive option to meet transient high energy density in operating fuel cells and in electric and hybrid electric vehicles. To achieve such requirements, intensive studies have been carried out to improve the volumetric capacitance in supercapacitors using various types and forms of carbons including carbon nanotubes and graphenes. However, conventional porous carbons are not suitable for use as electrode material in supercapacitors for such high energy density applications. Here, we show that edge-enriched porous carbons are the best electrode material for high energy density supercapacitors to be used in vehicles as an auxiliary powertrain. Molten potassium hydroxide penetrates well-aligned graphene layers vertically and consequently generates both suitable pores that are easily accessible to the electrolyte and a large fraction of electrochemically active edge sites. We expect that our findings will motivate further research related to energy storage devices and also environmentally friendly electric vehicles.

Effect of dispersants of multi-walled carbon nanotubes on cellular uptake and biological responses

Although there have been many reports about the cytotoxicity of multi-walled carbon nanotubes (MWCNTs), the results are still controversial. To investigate one possible reason, the authors investigated the influence of MWCNT dispersants on cellular uptake and cytotoxicity. Cytotoxicity was examined (measured by alamarBlue® assay), as well as intracellular MWCNT concentration and cytokine secretion (measured by flow cytometry) in human bronchial epithelial cells (BEAS-2B) exposed to a type of highly purified MWCNT vapor grown carbon fiber (VGCF®, Shōwa Denkō Kabushiki-gaisha, Tokyo, Japan) in three different dispersants (gelatin, carboxylmethyl cellulose, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine). The authors also researched the relationship between the intracellular concentration of MWCNTs and cytotoxicity by using two cell lines, BEAS-2B and MESO-1 human malignant pleural mesothelioma cells. The intracellular concentration of VGCF was different for each of the three dispersants, and the levels of cytotoxicity and inflammatory response were correlated with the intracellular concentration of VGCF. A relationship between the intracellular concentration of VGCF and cytotoxic effects was observed in both cell lines. The results indicate that dispersants affect VGCF uptake into cells and that cytotoxicity depends on the intracellular concentration of VGCF, not on the exposed dosage. Thus, toxicity appears to depend on exposure time, even at low VGCF concentrations, because VGCF is biopersistent.

Carbonization under pressure

Carbonization under pressure was reviewed by being classified into three routes: carbonization of the precursors under pressure of their decomposition gases, carbonization under hydrothermal conditions, and reduction of pressurized CO2. Carbon materials with different structures and nanotextures were formed with relatively high yield under pressure, but obtained as a mixture in most cases. In this review, the formation conditions of carbon spheres in pure and an individually separated state are discussed by focusing on the temperature–pressure conditions and the chemical composition of the precursors used.

Simple Synthesis of Multiwalled Carbon Nanotubes from Natural Resources

The mass production of carbon nanotubes (CNTs) at low cost remains an important technological challenge if applications of CNTs are to be exploited further. Here, we report an extremely efficient method for growing pure and highly crystalline CNTs using natural resources: garnet powder as a catalyst, and city gas as a carbon source. The chemically reduced iron particles on the surface of the sand granules catalyze the decomposition of city gas, leading effectively to a high growth rate of CNTs. This novel method is very promising for providing lowcost, high-quality industrially available CNT products for developing large-scale applications in the near future. To produce CNTs in bulk quantities, a well-developed ironbased catalytic chemical vapor deposition (CCVD) method has been commonly used, as established by one of us after obtaining ultrathin hollow CNTs grown on nanosized iron particles. 2] However, for the production of CNTs, the catalyst is considered as one of the most expensive components. Therefore, to find an alternative cheap and effective catalyst for producing highquality and high-quantity CNTs remains a challenge for the bulk production of this key material in nanotechnology. Recently, Su and Chen reported the preparation of CNTs grown on lava rocks. However, those CNTs did not exhibit a well-ordered structure. In addition, the lava is not easy to handle in the CCVD process. Interestingly, one of us reported early on that the origin of the nanosized iron catalyst which promoted the production of a large amount of fibrous carbon material was the emery paper that was used for polishing the aluminum or graphite substrate used in the CCVD chamber. Later, it was found that brown emery paper is made of fine garnet powder. From this perspective, we report an alternative, environmentally friendly and efficient method for growing multiwalled carbon nanotubes (MWCNTs) using purely natural resources: stone garnet sand as a catalyst and support, and city gas based natural gas as the carbon source. Garnet powder consists of SiO2, FeO, Fe2O3, and Al2O3, among other things (Figure 1a) and is inexpensive (

Elucidation mechanism of different biological responses to multi-walled carbon nanotubes using four cell lines

1.4kg ). The size of the garnet sand particles is around 200 mm (see inset in Figure 1a). We