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Bimetallic NiFe alloys as highly efficient electrocatalysts for the oxygen evolution reaction
Lim, Dongwook,Oh, Euntaek,Lim, Chaewon,Shim, Sang Eun,Baeck, Sung-Hyeon Elsevier 2020 CATALYSIS TODAY - Vol.352 No.-
<P><B>Abstract</B></P> <P>In this study, binary NiFe alloy nanoparticles are successfully prepared using a simple hydrothermal method followed by H<SUB>2</SUB> reduction. The nanoparticles are then applied as electrocatalysts for oxygen evolution reaction (OER). Compared to unary Ni or Fe, the binary NiFe alloy electrocatalyst exhibits a much lower overpotential of 298 mV at a current density of 10 mA cm<SUP>−2</SUP>, and it exhibits electrocatalytic activity for OER superior to that of state-of-the-art RuO<SUB>2</SUB> and IrO<SUB>2</SUB> noble metal oxide catalysts. Moreover, the alloy catalyst exhibits substantial long-term durability after 1000 cyclic voltammetry tests. This remarkable electrochemical performance mainly originates from the synergistic effects of Fe incorporation into Ni species, leading to the improved charge transfer kinetics and intrinsic activity of the catalyst. These results provide a promising avenue for developing cost-effective and high-performance electrocatalysts as advanced electrodes for energy storage and conversion systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bimetallic Fe<SUB>0.64</SUB>Ni<SUB>0.36</SUB> Alloys were prepared by a hydrothermal method followed by mild H<SUB>2</SUB> reduction. </LI> <LI> The binary metal alloys exhibited a low overpotential and substantial long-term stability for oxygen evolution reaction. </LI> <LI> This outstanding OER performance and durability can be attributed to the synergistic effect of binary metal. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lim, Dongwook,Park, Taesoon,Choi, Yeji,Oh, Euntaek,Shim, Snag Eun,Baeck, Sung-Hyeon The Korean Electrochemical Society 2020 Journal of electrochemical science and technology Vol.11 No.2
Highly ordered mesoporous manganese oxide films were electrodeposited onto indium tin oxide coated (ITO) glass using sodium dodecyl sulfate (SDS) and ethylene glycol (EG) which were used as a templating agent and stabilizer for the formation of micelle, respectively. The manganese oxide films synthesized with surfactant templating exhibited a highly mesoporous structure with a long-range order, which was confirmed by SAXRD and TEM analysis. The unique porous structure offers a more favorable diffusion pathway for electrolyte transportation and excellent ionic conductivity. Among the synthesized samples, Mn<sub>2</sub>O<sub>3</sub>-SDS+EG exhibited the best electrochemical performance for a supercapacitor in the wide range of scan rate, which was attributed to the well-developed mesoporous structure. The Mn<sub>2</sub>O<sub>3</sub> prepared with SDS and EG displayed an outstanding capacitance of 72.04 F g<sup>-1</sup>, which outperform non-porous Mn<sub>2</sub>O<sub>3</sub> (32.13 F g<sup>-1</sup>) at a scan rate of 10 mV s<sup>-1</sup>.
Effect of proton irradiation on electrocatalytic properties of MnO2 for oxygen reduction reaction
Choi, Yeji,Lim, Dongwook,Oh, Euntaek,Lim, Chaewon,Baeck, Sung-Hyeon The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.19
<P>Significant efforts have been made to enhance the poor intrinsic electrocatalytic activity of MnO2 toward the oxygen reduction reaction (ORR) for practical applications in fuel cells and metal-air batteries. However, the main bottleneck problems of the MnO2 catalyst for the ORR include the poor conductivity and the low activity compared to state-of-the-art Pt/C. Here, high power proton particles (14 MeV) were irradiated on MnO2, and numerous oxygen vacancies were introduced into the surface of MnO2 by decomposing water radiolytically along the proton beam. Compared with the pristine MnO2, the proton-treated MnO2 showed a much higher current density of −4.6 mA cm<SUP>−2</SUP> at 0.65 V <I>vs.</I> reversible hydrogen electrode (RHE). The proton-treated MnO2 exhibited excellent catalytic durability, maintaining 95 % of its activity after a 10 000 s chronoamperometric stability test. This outstanding ORR performance and stability can be attributed to the improved physicochemical properties resulting from the proton beam irradiation. This study provides a novel approach for the generation of oxygen vacancies by proton irradiation, improving the catalyst for use as an advanced electrode material.</P>
Woo-Ghee Chung,박한규,Euntaek Lim,Jong-Gwan Yook 한국전자통신연구원 2007 ETRI Journal Vol.29 No.2
In this paper, we analyze the algorithm of the methodology developed by ITU for the calculation of spectrum requirements of IMT-Advanced. We propose an approach to estimate user density using traffic statistics, and to estimate spectrum efficiencies using carrier-to-interference ratio distribution and capacity theory as well as experimental data under Korean mobile communication environments. We calculate the IMT-Advanced spectrum requirements based on the user density and spectral efficiencies acquired from the new method. In the case of spectral efficiency using higher modulation and coding schemes, the spectrum requirement of IMT-Advanced is approximately 2700 MHz. When applying a 2×2 multiple-input multiple-output (MIMO) antenna system, it is approximately 1500 MHz; when applying a 4×4 MIMO antenna system, it is approximately 1050 MHz. Considering that the development of new technology will increase spectrum efficiency in the future, the spectrum requirement of IMT-Advanced in the Korean mobile communication environment is expected to be approximately 1 GHz bandwidth.
Cognitive Radio 시스템 환경에서의 다중 홉 릴레이 전송 기법
이동규(Dong-Kyu Lee),신정채(Jungchae Shin),임은택(Euntaek Lim),이현우(Hyeonwoo Lee),조호신(Ho-Shin Cho) 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.9A
본 논문에서는 IEEE 802.22 기반의 인지라디오 시스템에서 다중 홉 릴레이 방식의 적용 방안을 제안한다. 먼저, 중계기를 통한 전송 시나리오를 가정하고 이를 지원하기 위한 물리 채널 프레임 구조를 예시한다. 다음으로, 분산 감지 (distributed sensing) 방식을 이용한 가용 채널 결정 방식을 제안하고 이를 토대로, 기지국 중심의 중앙집중형 (centralized) 채널 할당 기법 및 릴레이 전송을 위한 중계기 선택 알고리즘을 개발하였다. 그리고 수학적 해석과 시뮬레이션을 통한 성능 분석 결과는 제안한 다중 홉 릴레이 방식이 중계기를 사용하지 않은 기존의 인지 라디오 시스템에 비해 스펙트럼 이용효율과 시스템 수율 측면에서 성능 향상이 있음을 보여준다. In this paper, a multi-hop relaying transmission scheme is analyzed regarding its feasibility and potentiality in the IEEE 802.22-based cognitive radio (CR) environment. Shortly, basic design issues are addressed such as relay station (RS) deployment and a frame structure of physical channel to escape inter-hop interference. This paper mainly develops a radio resource management scheme based on spectrum sensing results aggregated from CR secondary nodes and improves the opportunistic spectrum sharing efficiency. In particular, a decision rule about a channel availability is made using a distributed sensing method. Subsequently, spectrum allocation and routing path decision procedures are proposed to establish a link from source to destination with a hop-by-hop manner. Simulation results show that the proposed multi-hop relaying scheme is substantially profitable in CR environments if the number of hops and RS deployment are designed in such a way that the spectrum sharing gain is larger than spectrum division loss which is inherently induced in multi-hop relaying systems.
정전류/정출력 고속충전 방식에 따른 리튬이온전지의 열화 비교 연구
박선호,오은택,박시영,임지훈,최진혁,이용민,Park, Sun Ho,Oh, Euntaek,Park, Siyoung,Lim, Jihun,Choi, Jin Hyeok,Lee, Yong Min 한국전력공사 2020 KEPCO Journal on electric power and energy Vol.6 No.2
전기자동차의 보급이 확대됨에 따라, 소비자의 고속충전에 요구가 높아지고 있으나 관련 연구는 미흡한 실정이다. 본 연구에서는 LiNi<sub>0.5</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub>O<sub>2</sub>/Graphite 18650 실린더형 리튬이온전지를 이용하여, 정전류와 정출력 충전방식에 따른 전지 열화현상을 비교한다. 정전류모드의 충전속도를 1C, 2C, 3C, 4C로 설정하고, 각 충전속도에서의 에너지를 기반으로 정출력값을 산정하였다. 따라서, 동일 충전 에너지를 기반하여, 두 충전방식에 따른 전지 열화를 분석한 결과, 3C의 높은 율속에서 정출력 충전방식이 전지의 열화를 늦출 수 있음이 전압곡선, 용량유지율, 직류저항값으로 확인되었다. 그러나, 충전속도를 4C 이상 높이면, 충전방식보다 전지간 편차가 열화 거동을 지배하였다. Electric vehicles (EVs) using lithium secondary batteries (LIBs) with excellent power and long-term cycle performance are gaining interest as the successors of internal combustion engine (ICE) vehicles. However, there are few systematic researches for fast charging to satisfy customers' needs. In this study, we compare the degradation of LIB where its composition is LiNi<sub>0.5</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub>/Graphite with the constant current and constant power-charging method. The charging speed was set to 1C, 2C, 3C and 4C in the constant current mode and the value of constant power was calculated based on the energy at each charging speed. Therefore, by analyzing the battery degradation based on the same charging energy but different charging method; CP charging method can slow down the battery degradation at a high rate of 3C through the voltage curve, capacity retention and DC-IR. However, when the charging rate was increased by 4C or more, the deviation between the LIBs dominated the degradation than the charging method.