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47 results on '"Seung, Doyoung"'

43. Understanding a Degradation Mechanism of Direct Methanol Fuel Cell Using TOF-SIMS and XPS

Author

Chung, Youngsu, Pak, Chanho, Park, Gyeong-Su, Sung Jeon, Woo, Kim, Ji-Rae, Lee, Yoonhoi, Chang, Hyuk, and Seung, Doyoung

Abstract

The catalyst layers, which were obtained from the aged membrane electrode assemblies (MEAs) showing performance loss, 17%, 37%, 45% as compared with that from the pristine MEA were investigated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) to understand the degradation mechanism of single-cell performance in direct methanol fuel cell. The metallic components in the PtRu anode catalyst layer was decreased significantly with the performance drop revealed from the change of the valance bands. It has been found that ruthenium and platinum were driven to the cathode by the gradient of electric field during the durability test. From the mass-resolved imaging technique of TOF-SIMS combined with a peel-off method, it was indicated that the traveled ruthenium from anode to cathode was not uniformly distributed within the cathode catalyst layer, but more accumulated at the surface of the catalyst layer, that is, the interface with the gas diffusion layer. XPS and TOF-SIMS results suggested that the ruthenium ions are electro-deposited to RuOxrather than metallic Ru, which seems to more closely correlate with the degradation of performance.

Published
2008
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44. Surface Selective Polymerization of Polypyrrole on Ordered Mesoporous Carbon:  Enhancing Interfacial Conductivity for Direct Methanol Fuel Cell Application

Author

Suk Choi, Yeong, Hoon Joo, Sang, Lee, Seol-Ah, Jong You, Dae, Kim, Hansu, Pak, Chanho, Chang, Hyuk, and Seung, Doyoung

Abstract

Ordered mesoporous carbon (OMC) selectively covered on the outer surface with polypyrrole (PPy) was prepared by removing the mesoporous silica template after the polymerization of pyrrole adsorbed on the surface of mesoporous silica−carbon composite. The amounts of PPys loaded on OMCs increased with the polymerization time and adsorption time. The resulting PPy−OMC composite maintained regular mesopore structure and high surface area of the OMC. The electrical resistance of PPy−OMC showed a lower value than that of pristine OMC; however, at high loading amount of PPy, the resistance rised to the value of pristine OMC. The PPy−OMC was successfully used as supports for Pt metal particles with a size of 2.8 nm, which illustrated that inner pores of the OMC were effectively utilized for supporting Pt catalyst particles even in the presence of PPy. Furthermore, the electrochemically active surface area obtained from the cyclic voltammogram of Pt catalyst loaded in the PPy−OMC was much higher than that of a commercial catalyst. The Pt-loaded PPy−OMC catalyst exhibited 50% enhanced power density compared to the commercial Pt catalyst in a direct methanol fuel cell (DMFC) single cell test. These results indicated that the PPy−OMC could afford plenty of surface area for supporting the Pt particles in the mesopores, and the Pt particles in PPy−OMCs were applicable to direct methanol fuel cells.

Published
2006

45. Rational design of ordered mesoporous carbon with controlled bimodal porosity viadual silica templating routeElectronic supplementary information (ESI) available: Fig. S1–S3. See DOI: 10.1039/b511423c

Author

Lee, Hyung Ik, Pak, Chanho, Shin, Chae-Ho, Chang, Hyuk, Seung, Doyoung, Yie, Jae Eui, and Kim, Ji Man

Abstract

Combining both nano-replication and nano-imprinting techniques using dual silica templates provides a simple way to synthesize ordered mesoporous carbons with bimodal pore size distributions (∼1.5 nm and ∼3.5 nm).

Published
2005
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46. Synthesis and characterization of nanostructured PtCo-CeO x /C for oxygen reduction reaction

Author

Lee, Kang Hee, Kwon, Kyungjung, Roev, Victor, Yoo, Duck Young, Chang, Hyuk, and Seung, Doyoung

Subjects
*PLATINUM compounds, *NANOSTRUCTURED materials, *ORGANIC synthesis, *OXIDATION-reduction reaction, *PROTON exchange membrane fuel cells, *COBALT alloys, *ELECTROCATALYSIS
Abstract

Abstract: Highly dispersed PtCo–CeO x couples of fine Pt3Co alloy particles with adjacent CeO x are synthesized on a carbon support using the modified colloid method. The average sizes of Pt3Co and CeO x particles are approximately 1.7 and 4nm, respectively. According to XPS studies, the CeO x particle consists of a CeO2 phase crystal for the core and a Ce2O3 phase for the shell. The CeO x -containing electrocatalysts of PtCo–CeO x and Pt–CeO x show improved electrochemical performances for the oxygen reduction reaction compared with PtCo and Pt electrocatalysts without CeO x in both ring-disc electrode and cell tests. It seems that the unsaturated Ce2O3 phase of the CeO x surface causes the facile adsorption and desorption of oxygen, leading to an enhanced oxygen supply to the PtCo alloy. [Copyright &y& Elsevier]

Published
2008
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47. Determination of bidirectional permeability of proton exchange membranes using a 1H nuclear magnetic resonance technique

Author

Kim, Eun Ah, Kim, Tae Kyoung, Pak, Chanho, Chang, Hyuk, Seung, Doyoung, and Choi, Yeong Suk

Subjects
*MAGNETIC permeability, *NUCLEAR magnetic resonance spectroscopy, *PROTON exchange membrane fuel cells, *PHYSICAL & theoretical chemistry
Abstract

Abstract: Bidirectional permeability of proton exchange membranes was measured using a 1H nuclear magnetic resonance (NMR) technique based on the assignment of characteristic peaks and derivation of a relationship between the peak areas and the concentrations of methanol, water and D2O. The concentration variations of the liquids determined with NMR spectra showed that both methanol and the water transports were affected by the thickness and the chemical structure of membranes. Molar ratios of methanol to water diffused through membranes elucidated that chemical structures of membranes had a strong influence on the methanol transport, compared to thickness. Reverse-direction diffusion behaviors of membranes, back-diffusions, were also appraised with the D2O amounts. The amounts of back-diffusions were much less than those of the water transported from the opposite direction, which is the first report on the direct measurements of back-diffusions. The results suggest that 1H NMR technique can evaluate bidirectional transports of proton exchange membranes. [Copyright &y& Elsevier]

Published
2008
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