DSpace Community: KAIST College of Natural SciencesKAIST College of Natural Scienceshttp://hdl.handle.net/10203/112018-05-04T06:20:24Z2018-05-04T06:20:24ZPromotion of electrochemical oxygen evolution reaction by chemical coupling of cobalt to molybdenum carbideKim, MinJoongKim, SunghyunSong, DongHoonOh, Se-KwonChang, Kee JooCho, EunAehttp://hdl.handle.net/10203/2413972018-04-24T06:32:03Z2018-07-01T00:00:00ZTitle: Promotion of electrochemical oxygen evolution reaction by chemical coupling of cobalt to molybdenum carbide
Authors: Kim, MinJoong; Kim, Sunghyun; Song, DongHoon; Oh, Se-Kwon; Chang, Kee Joo; Cho, EunAe
Abstract: Herein, we report a novel strategy to promote electrochemical oxygen evolution reaction (OER) on cobalt (Co) surface by coupling Co to molybdenum carbide (Mo2C). Chemically coupled Co and Mo2C nanoparticles were synthesized through a simple heat treatment of the mixture containing Co and Mo precursors and graphitic carbon nitride (g-C3N4). Transmission electron microscopy (TEM) images obviously showed that Co and Mo2C nanoparticles were coupled at Co/Mo2C interfaces. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation results revealed that electrons were transferred from Co to Mo2C nanoparticles across the interfaces. The electron transfer makes the Co surface more electrophilic by d-band center of Co upshift, leading to an increase in OH- affinity. As a result, the Co nanoparticles coupled with Mo2C have OER-favorable Co-oxo and Co-hydroxo configuration within their oxidized surfaces, and hence, can accelerate the overall OER than bare Co nanoparticles. This work demonstrates that the Co nanoparticles chemically coupled to Mo2C exhibited excellent OER activity and stability in an alkaline electrolyte and suggests a promising way to design an active OER catalyst.2018-07-01T00:00:00ZSingly periodic free boundary minimal surfaces in a solid cylinder of H-2 x RMorabito, Filippohttp://hdl.handle.net/10203/2414012018-04-24T06:32:14Z2018-06-01T00:00:00ZTitle: Singly periodic free boundary minimal surfaces in a solid cylinder of H-2 x R
Authors: Morabito, Filippo
Abstract: The aim of this work is to show there exist free boundary minimal surfaces of Saddle Tower type which are embedded in a vertical solid cylinder of H-2 x R, H-2 being the hyperbolic plane, and invariant under the action of a vertical translation and a rotation. The number of boundary curves equals 2l, l >= 2. These surfaces come in families depending on one parameter and they converge to 2l vertical stripes having a common intersection line. (c) 2018 Elsevier Ltd. All rights reserved.2018-06-01T00:00:00ZThree Transition Regions Observed in Single Crystalline Bi-Rich Bi2Te3 NanobeltsLee, SunghunIn, June-HoJi, SanghyunPark, Yun ChangKim, JinheeKim, BongsooJung, Myung-Hwahttp://hdl.handle.net/10203/2401912018-02-21T06:02:06Z2018-05-01T00:00:00ZTitle: Three Transition Regions Observed in Single Crystalline Bi-Rich Bi2Te3 Nanobelts
Authors: Lee, Sunghun; In, June-Ho; Ji, Sanghyun; Park, Yun Chang; Kim, Jinhee; Kim, Bongsoo; Jung, Myung-Hwa
Abstract: Bi2Te3 has recently received considerable attention because of its various characteristics and applications potential. The effort to incorporate dopants into Bi2Te3 to achieve particular features has continued. We investigated Bi-rich Bi2Te3 nanobelts, which were synthesized by the VLS method. We confirmed that single crystalline Bi-rich Bi2Te3 nanobelts with 1:1 of Bi:Te atomic ratio had a hexagonal Bi2Te3 crystal structural phase, using X-ray diffraction and scanning transmission electron microscopy. The results from electrical and magneto-transport measurements of a Bi-rich Bi2Te3 nanodevice revealed three different transition regions, in which different magnetoresistance behaviors were observed, and where the maximum magnetoresistanee ratio was about 105%. These characteristics could provide a wider perspective for potential of Bi-rich Bi2Te3 nanodevices.2018-05-01T00:00:00ZAverage values of L-functions in even characteristicBae, SunghanJung, Hwanyuphttp://hdl.handle.net/10203/2405842018-03-21T02:20:41Z2018-05-01T00:00:00ZTitle: Average values of L-functions in even characteristic
Authors: Bae, Sunghan; Jung, Hwanyup
Abstract: Let k = F-q(T) be the rational function field over a finite field F-q, where q is a power of 2. In this paper we solve the problem of averaging the quadratic L-functions L(s, chi(u)) over fundamental discriminants. Any separable quadratic extension K of k is of the form K = k(x(u)), where x(u) is a zero of X-2 + X + u = 0 for some u is an element of k. We characterize the family I (resp. F, F') of rational functions u is an element of k such that any separable quadratic extension K of k in which the infinite prime infinity = (1/T) of k ramifies (resp. splits, is inert) can be written as K = k(x(u)) with a unique u is an element of I (resp. u is an element of F, u is an element of F'). For almost all s is an element of C with Re(s) >= 1/2, we obtain the asymptotic formulas for the summation of L(s,chi(u)) over all k(x(u)) with u is an element of I, all k(x(u)) with u is an element of F or all k(x(u)) with u is an element of F' of given genus. As applications, we obtain the asymptotic mean value formulas of L-functions at s = 1/2 and s = 1 and the asymptotic mean value formulas of the class number h(u) or the class number times regulator h(u)R(u). (C) 2017 Elsevier Inc. All rights reserved.2018-05-01T00:00:00Z