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Hwang, Seung Jun,Kim, Soo-Kil,Lee, June-Gunn,Lee, Seung-Cheol,Jang, Jong Hyun,Kim, Pil,Lim, Tae-Hoon,Sung, Yung-Eun,Yoo, Sung Jong American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.48
<P>The design of electrocatalysts for polymer electrolyte membrane fuel cells must satsify two equally important fundamental principles: optimization of electrocatalytic activity and long-term stability in acid media (pH <1) at high potential (0.8 V). We report here a solution-based approach to the preparation of Pt-based alloy with early transition metals and realistic parameters for the stability and activity of Pt(3)M (M = Y, Zr, Ti, Ni, and Co) nanocatalysts for oxygen reduction reaction (ORR). The enhanced stability and activity of Pt-based alloy nanocatalysts in ORR and the relationship between electronic structure modification and stability were studied by experiment and DFT calculations. Stability correlates with the d-band fillings and the heat of alloy formation of Pt(3)M alloys, which in turn depends on the degree of the electronic perturbation due to alloying. This concept provides realistic parameters for rational catalyst design in Pt-based alloy systems.</P>
Plasmon-Enhanced Ultraviolet Photoluminescence from Hybrid Structures of Graphene/ZnO Films
Hwang, Sung Won,Shin, Dong Hee,Kim, Chang Oh,Hong, Seung Hui,Kim, Min Choul,Kim, Jungkil,Lim, Keun Yong,Kim, Sung,Choi, Suk-Ho,Ahn, Kwang Jun,Kim, Gunn,Sim, Sung Hyun,Hong, Byung Hee American Physical Society 2010 Physical Review Letters Vol.105 No.12
<P>We report substantially enhanced photoluminescence (PL) from hybrid structures of graphene/ZnO films at a band gap energy of ZnO (??.3??eV/376??nm). Despite the well-known constant optical conductivity of graphene in the visible-frequency regime, its abnormally strong absorption in the violet-frequency region has recently been reported. In this Letter, we demonstrate that the resonant excitation of graphene plasmon is responsible for such absorption and eventually contributes to enhanced photoemission from structures of graphene/ZnO films when the corrugation of the ZnO surface modulates photons emitted from ZnO to fulfill the dispersion relation of graphene plasmon. These arguments are strongly supported by PL enhancements depending on the spacer thickness, measurement temperature, and annealing temperature, and the micro-PL mapping images obtained from separate graphene layers on ZnO films.</P>
Yoo, Sung Jong,Hwang, Seung Jun,Lee, June-Gunn,Lee, Seung-Cheol,Lim, Tae-Hoon,Sung, Yung-Eun,Wieckowski, Andrzej,Kim, Soo-Kil The Royal Society of Chemistry 2012 ENERGY AND ENVIRONMENTAL SCIENCE Vol.5 No.6
<P>The design of polymer electrolyte fuel cell electrocatalysts depends on two equally important fundamental principles: the optimization of electrocatalytic activities as well as the long-term stability under operating conditions (<I>e.g.</I>, pH < 1 and <I>E</I> > 0.8 V). Pt-based alloys with transition metals (<I>i.e.</I>, Pt–La) address both of these key issues. The oxygen reduction kinetics depends on the alloy composition which, in turn, is related to the d-band center position. The stability of the oxygen reduction reaction is predictable by correlation of the d-band fillings and vacancies of Pt–M (M = Ti, Fe, Zr and La).</P> <P>Graphic Abstract</P><P>Substantially improved ORR activity and stability of the Pt<SUB>3</SUB>La alloy electrode have been demonstrated and explained in terms of the electronic effects. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ee02691k'> </P>
Development of a Flat-Plate Cooling Device for Electronic Packaging
Seok-Hwan Moon,Gunn Hwang,Hyun-Taeck Lim 한국전자통신연구원 2011 ETRI Journal Vol.33 No.4
In this study, a microcapillary pumped loop (MCPL) that can be used as a cooling device for small electronic and telecommunications equipment has been developed. For thin devices such as an MCPL, securing a vapor flow space is a critical issue for enhancing the thermal performance. In this letter, such enhancement in thermal performance was accomplished by eliminating condensed droplets from the vapor line. By fabricating the grooves in the vapor line to eliminate droplets, a decrease in thermal resistance of about 63.7% was achieved.