Publications (7)10.44 Total impact
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Article: Electrocatalytic effects of carbon dissolution in Pd nanoparticles.
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ABSTRACT: Highly dispersed Pd nanoparticles were prepared by borohydride reduction of Pd(acac)(2) in 1,2-propanediol at an elevated temperature. They were uniformly dispersed on carbon black without significant aggregation. X-ray diffraction showed that carbons from the Pd precursor dissolved in Pd, increasing its lattice parameter. A modified reduction process was tested to remove the carbon impurities. Carbon removal greatly enhanced catalytic activity toward the oxygen reduction reaction. It also generated an inconsistency between the electronic modifications obtained from X-ray photoelectron spectroscopy and the electrochemical method. CO displacement measurements showed that the formation of Pd-C bonds decreased the work function of the surface Pd atoms.Langmuir 02/2012; 28(7):3664-70. · 4.19 Impact Factor -
Article: Preparation of mesoporous carbon-carbon nanotube composites using the template method.
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ABSTRACT: Reported herein is a simple template method for preparing mesoporous carbons (MPCs) from a mesophase pitch, using homemade nano-sized MgOs and MgO-carbon nanotube (CNT) composites as templates. Nano-sized MgO particles containing iron-molybdenum were synthesized through the heat treatment of the precursor ash, and the MgO-CNT composites were prepared via catalytic chemical vapor deposition of CH4 over the MgO-based particles. MPCs with a high surface area of 443-578 m2/g were obtained through the heat treatment of well-mixed mesophase pitch-MgO (or MgO-CNT), followed by mild-acid treatment to remove the MgO and other catalyst components. All the materials (the precursors, nano-particles, and MPCs) were analyzed via powder X-ray diffraction, N2 adsorption-desorption isotherms, scanning electron microscopy, and high resolution transmission electron microscopy. The formation of the pore structure in the MPCs is discussed, and the potential application of the MPC-CNT composite is demonstrated through cyclic voltammetry.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5761-8. · 1.56 Impact Factor -
Article: Characteristics of porous carbon nano-fibers synthesized by selective catalytic gasification.
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ABSTRACT: Carbon nanofibers (CNFs) with uniquely oriented channels were prepared via selective catalytic gasification in air at 450 and 500 degrees C, using Pt or Ru nano particles as catalysts. Catalytic gasification was chosen because it can selectively generate channels in the vicinity of the catalyst particles at relatively low temperatures, where thermal oxidation does not intensively occur. The structures and surface properties of the CNFs were examined via X-ray diffraction, analysis of the nitrogen adsorption-desorption isotherms, and high-resolution transmission electron microscopy. The effects of the catalyst species and loading amount on the formation of pores (channels) were investigated. The gasification mechanism, especially the channeling direction, throught the selection of the gasification catalysts, is discussed based on the results. This process can be effectively utilized for preparation of porous carbons, which have a well-aligned graphitic structure, and also channel-type pores can be designed by selection of gasification catalysts and conditions. The present porous CNF can be applied for catalyst support in fuel cells, without further treatment (e.g., acid treatment for the removal of metallic components).Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5775-80. · 1.56 Impact Factor -
Article: Electrochemical catalytic activity for oxygen reduction reaction of nitrogen-doped carbon nanofibers.
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ABSTRACT: The electrocatalytic activity of nitrogen-doped carbon nanofibers (N-CNFs), which are synthesized directly from vaporized acetonitrile over nickel-iron based catalysts, for oxygen reduction reaction (ORR), was investigated. The nitrogen content and specific surface area of N-CNFs can be controlled through the synthesis temperature (300-680 degrees C). The graphitization degree of N-CNFs also are significantly affected by the temperature, whereas the chemical compositions of nitrogen species are similar irrespective of the synthesis conditions. From measurement of the electrochemical double layer capacitance, the surface of N-CNFs is found to have stronger interaction with ions than undoped-carbon surfaces. Although N-CNFs show higher over-potential than Pt catalysts do, N-CNFs were observed to have a noticeable ORR activity, as opposed to the carbon samples without nitrogen doping. The activity dependency of N-CNFs on the content of the nitrogen with which they were doped is discussed, based on the experiment results. The single cell of the direct methanol fuel cell (DMFC) was tested to investigate the performance of a membrane-electrode assembly that includes N-CNFs as the cathode catalyst layer.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):6350-8. · 1.56 Impact Factor -
Article: Study on the water flooding in the cathode of direct methanol fuel cells.
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ABSTRACT: Water flooding phenomena in the cathode of direct methanol fuel cells were analyzed by using electrochemical impedance spectroscopy. Two kinds of commercial gas diffusion layers with different PTFE contents of 5 wt% (GDL A5) and 20 wt% (GDL B20) were used to investigate the water flooding under various operating conditions. Water flooding was divided into two types: catalyst flooding and backing flooding. The cathode impedance spectra of each gas diffusion layer was obtained and compared under the same conditions. The diameter of the capacitive semicircle became larger with increasing current density for both, and this increase was greater for GDL B20 than GDL A5. Catalyst flooding is dominant and backing flooding is negligible when the air flow rate is high and current density is low. An equivalent model was suggested and fitted to the experimental data. Parameters for catalyst flooding and backing flooding were individually obtained. The capacitance of the catalyst layer decreases as the air flow rate decreases when the catalyst flooding is dominant.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5788-94. · 1.56 Impact Factor -
Chapter: Development of A 5-W Direct Methanol Fuel Cell Stack for DMB Phone
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ABSTRACT: As high-tech multifunctional and miniature devices such as laptop computers, digital video recorders, digital multimedia phones, PDAs, and electronic game players become more widely used, new power sources need to be developed that have much longer run time and stronger power than those that current power sources, namely lithium batteries, provide. A fuel cell, which is a device that generates electricity by a chemical reaction, is considered the promising candidate for replacing them. Among various fuel cells, direct methanol fuel cell (DMFC) is the most suitable power source because it does not require any fuel processing equipment and can be operated at low temperatures. Also DMFC has advantages of easy transportation and storage of the fuel, and reduced system weight and size. However, in order to develop a micro fuel cell needs much examination due to a limited weight and size and a high performance, durability. To meet these requirements, the MEA has to perform well and the stack design has to be very compact. We have developed a 5-W DMFC stack for DMB phones. This paper describes the design of the micro fuel cell system and stack and flow field. We also investigated the feasibility of metal bipolar plates to decrease the volume and cost of the stack. It was fabricated with five cells having an electrode area of 131 cm2 and has the internal manifolds for supply of air and fuel. The electrochemical performance of the single cell and the stack was evaluated.10/2008: pages 269-289; -
Article: Operating characteristics of direct methanol fuel cell using a platinum–ruthenium catalyst supported on porous carbon prepared from mesophase pitch
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ABSTRACT: The characteristics of a platinum–ruthenium catalyst supported on porous carbon (PC) are analysed by X-ray diffraction, scanning electron microscopy, cyclic voltammetry and chemisorption techniques. Single-cell tests are carried out in order to compare the performance of these catalysts as an anode in a direct methanol fuel cell with respect to that of a commercial-grade catalyst. The methanol oxidation rate on a Pt–Ru catalyst supported on PC with a pore size of 20 nm is about 35% higher than that on a commercial E-TEK catalyst. The catalyst (Pt–Ru/K20) in the single-cell test gives a power density of 90 and 126 mW cm−2 under air and oxygen at 60 °C, respectively. These values are 15–16% higher than those obtained with a commercial E-TEK catalyst.Journal of Power Sources.
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Institutions
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2011
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Korea Institute of Energy Research
Seoul, Seoul, South Korea
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