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Synthesis of a New Cathode Redox Polymer for High Performance in Biofuel Cells

  • Choi, Young-Bong;Lee, Jung-Min;Kim, Hyug-Han
    • Bulletin of the Korean Chemical Society
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    • v.35 no.9
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    • pp.2803-2808
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    • 2014
  • High potential and fast electron transfer of a cathode mediator are significant factors for improving the performance of biofuel cells. This paper reports the first synthesis of a cathode redox polymer that is a coordination complex of poly (acrylic acid-vinylpyridine-acryl amide) (PAA-PVP-PAA) and [Os(4,4'-dicarboxylic acid-2,2'-bipyridine)2Cl2]/+ (E=0.48V versus Ag/AgCl). Bilirubin oxidase can be easily incorporated into this polymer matrix, which carried out the four-electron oxygen under typical physiological conditions (pH 7.2, 0.14 M NaCl, and 37C). This new polymer showed an approximately 0.1 V higher redox potential than existing cathode mediators such as PAA-PVI-[Os(dClbpy)2Cl]+/2+. In addition, we suggest increasing the polymer solubility with two hydrophilic groups present in the polymer skeleton to further improve fast electron transfer within the active sites of the enzyme. The maximum power density achieved was 60% higher than that of PAA-PVI-[Os(dClbpy)2Cl]+/2+. Furthermore, high current density and electrode stability were confirmed for this osmium polymer, which makes it a promising candidate for high-efficiency biofuel cells.

A Study on Corrosion CoCrMo Magnetic Thin Films (CoCrMo 자성박막의 부식에 관한 연구)

  • 남인탁;홍양기
    • Journal of the Korean Magnetics Society
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    • v.3 no.3
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    • pp.221-228
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    • 1993
  • The general requirements of recording media include recording performance, environmental stability, runnability on the drive or deck, and manufacturability. CoCrMo thin films were prepared using RF sputtering system for a study on chemical stability. Surface degradation of the CoCrMo thin film was studied by SEM, XPS and AES. Surface degradation was found to be dependent of sputtering condition and Mo content. Addition of Mo to CoCr thin film improved dramatically its surface degradation resistance in dilute sulfuric acid, as indicated by active-passive transition appeared in electrochemical polarization curve. Futhermore, the passive current density was decreased with increasing Mo content. The reduction in a number density of corrosion sites by Mo addition vms observed, after accelerated corrosion test. AES survey indicated that corrosion occured on the site with Cr depletion and highly concentrated chloride ions.

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The Surface Modification of Electrode with Solid Electrolyte Interphase for Hybrid Supercapacitor

  • Choi, Min-Geun;Kang, Soo-Bin;Yoon, Jung Rag;Lee, Byung Gwan;Jeong, Dae-Yong
    • Journal of Electrical Engineering and Technology
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    • v.10 no.3
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    • pp.1102-1106
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    • 2015
  • A hybrid supercapacitor (HS) is an energy storage device used to enhance the low weight energy density (Wh/kg) of a supercapacitor. On the other hand, a sudden decrease in capacity has been pointed out as a reliability problem after many charge/discharge cycles. The reliability problem of a HS affects the early aging process. In this study, the capacity performance of a HS was observed after charge/discharge. For detailed analysis of the initial charge/discharge cycles, the charge and discharge curve was measured at a low current density. In addition, a solid electrolyte interphase (SEI) layer was confirmed after the charge/discharge. A HC composed of a lithium titanate (LTO) anode and active carbon cathode was used. The charge/discharge efficiency of the first cycle was lower than the late cycles and the charge/discharge rate was also lower. This behavior was induced by SEI layer formation, which consumed Li ions in the LTO lattice. The formation of a SEI layer after the charge/discharge cycles was confirmed using a range of analysis techniques.

A Study on the Electrical Characteristics of Battery Capacitor Applied to Photovoltaic Power System (태양광 시스템에 적용한 배터리 커패시터의 전기적 특성에 관한 연구)

  • Mang, Ju-Cheul;Yoon, Jung-Rag
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.66 no.12
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    • pp.1740-1744
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    • 2017
  • This paper describes the preparation and characteristics of a battery capacitor and module for solar power system. A cylindrical 30,000F battery capacitor (60×138mm) was assembled by using the LTO(Li4Ti5O12) electrode as an anode and NMC(LiNiMnCoO2)LCO(LiCoO2) as a cathode. The battery capacitor has reduced energy density and power density under high CC(constant current) and CP(constant power) conditions. Battery capacitor module (16V, 11Ah) was fabricated using an asymmetric hybrid capacitor with a capacitance of 30,000F. In order to determine the characteristics of the battery capacitor Module for solar power system, battery capacitor cells were connected in series with active balancing circuit. As a result of measuring the 100w LED lamp, it was discharged at the voltage of 15V~10V, and the compensation time at discharge was measured to be about 4979s. Experimental results show that it can be applied to applications related to solar power system by applying battery capacitor module.

An efficient reliability analysis strategy for low failure probability problems

  • Cao, Runan;Sun, Zhili;Wang, Jian;Guo, Fanyi
    • Structural Engineering and Mechanics
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    • v.78 no.2
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    • pp.209-218
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    • 2021
  • For engineering, there are two major challenges in reliability analysis. First, to ensure the accuracy of simulation results, mechanical products are usually defined implicitly by complex numerical models that require time-consuming. Second, the mechanical products are fortunately designed with a large safety margin, which leads to a low failure probability. This paper proposes an efficient and high-precision adaptive active learning algorithm based on the Kriging surrogate model to deal with the problems with low failure probability and time-consuming numerical models. In order to solve the problem with multiple failure regions, the adaptive kernel-density estimation is introduced and improved. Meanwhile, a new criterion for selecting points based on the current Kriging model is proposed to improve the computational efficiency. The criterion for choosing the best sampling points considers not only the probability of misjudging the sign of the response value at a point by the Kriging model but also the distribution information at that point. In order to prevent the distance between the selected training points from too close, the correlation between training points is limited to avoid information redundancy and improve the computation efficiency of the algorithm. Finally, the efficiency and accuracy of the proposed method are verified compared with other algorithms through two academic examples and one engineering application.

Enhanced Luminous Intensity in LEDs with Current Blocking Layer (전류 차단 층을 갖는 LED의 향상된 광세기)

  • Yoon, Seok-Beom;Kwon, Kee-Young;Choi, Ki-Seok
    • Journal of Digital Convergence
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    • v.12 no.7
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    • pp.291-296
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    • 2014
  • Inserting a SiO2 layer underneath the p-pad electrode as the current blocking layer (CBL) structure and extending p-metal finger patterns, the GaN LEDs using an indium-tin-oxide (ITO) layer show the improved light output intensity, resulting from better current spreading and reduced light loss on the surface of p-pad metal. The LEDs with an oxide layer of 100μm-pad-width and 6μm-finger-width have better light output intensities than those with an oxide layer of 105μm-pad-width and 12μm-finger-width. Using the ATLAS device simulator from Silvaco Corporation, the current density distributions on the active layer in CBL LEDs have been investigated.

Proposed Guidelines for Selection of Methods for Erosion-corrosion testing in Flowing Liquids

  • Matsumura, Masanobu
    • Corrosion Science and Technology
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    • v.6 no.6
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    • pp.291-296
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    • 2007
  • The corrosion of metals and alloys in flowing liquids can be classified into uniform corrosion and localized corrosion which may be categorized as follows. (1) Localized corrosion of the erosion-corrosion type: the protective oxide layer is assumed to be removed from the metal surface by shear stress or turbulence of the fluid flow. A macro-cell may be defined as a situation in which the bare surface is the macro-anode and the other surface covered with the oxide layer is the macro-cathode. (2) Localized corrosion of the differential flow-velocity corrosion type: at a location of lower fluid velocity, a thin and coarse oxide layer with poor protective qualities may be produced because of an insufficient supply of oxygen. A macro-cell may be defined as a situation in which this surface is the macro-anode and the other surface covered with a dense and stable oxide layer is the macro-cathode. (3) Localized corrosion of the active/passive-cell type: on a metal surface a macro-cell may be defined as a situation in which a part of it is in a passivation state and another in an active dissolution state. This situation may arise from differences in temperature as well as in the supply of the dissolved oxygen. Compared to uniform corrosion, localized corrosion tends to involve a higher wall thinning rate (corrosion rate) due to the macro-cell current as well as to the ratio of the surface area of the macro-anode to that of the macro-cathode, which may be rationalized using potential vs. current density diagrams. The three types of localized corrosion described above can be reproduced in a Jet-in-slit test by changing the flow direction of the test liquid and arranging environmental conditions in an appropriate manner.

Numerical Study on Oxygen Depletion Characteristics of Porous Cathodes in Anode-Supported Solid Oxide Fuel Cells (음극지지 고체산화물 연료전지 다공성 양극에서의 산소고갈 특성에 관한 수치해석 연구)

  • Shin, Dongwoo;Nam, Jin Hyun;Kim, Charn-Jung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.4
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    • pp.257-268
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    • 2017
  • This paper proposes an efficient two-dimensional simulation model for solid oxide fuel cells (SOFCs) based on the electrochemical effectiveness model. The effectiveness model is known to accurately predict the current generation performance of SOFC electrodes, by considering the complex reaction/transport processes that occur within thin active functional layers near the electrolyte. After validation tests, the two-dimensional simulation model was used to calculate the distribution of current density and oxygen concentration transverse to the flow channel in anode-supported SOFCs, with which the oxygen depletion characteristics were investigated in detail. In addition, simulations were also conducted to determine the minimum number of grids required in the transverse direction to efficiently obtain accurate results.

Visual Explanation of a Deep Learning Solar Flare Forecast Model and Its Relationship to Physical Parameters

  • Yi, Kangwoo;Moon, Yong-Jae;Lim, Daye;Park, Eunsu;Lee, Harim
    • The Bulletin of The Korean Astronomical Society
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    • v.46 no.1
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    • pp.42.1-42.1
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    • 2021
  • In this study, we present a visual explanation of a deep learning solar flare forecast model and its relationship to physical parameters of solar active regions (ARs). For this, we use full-disk magnetograms at 00:00 UT from the Solar and Heliospheric Observatory/Michelson Doppler Imager and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, physical parameters from the Space-weather HMI Active Region Patch (SHARP), and Geostationary Operational Environmental Satellite X-ray flare data. Our deep learning flare forecast model based on the Convolutional Neural Network (CNN) predicts "Yes" or "No" for the daily occurrence of C-, M-, and X-class flares. We interpret the model using two CNN attribution methods (guided backpropagation and Gradient-weighted Class Activation Mapping [Grad-CAM]) that provide quantitative information on explaining the model. We find that our deep learning flare forecasting model is intimately related to AR physical properties that have also been distinguished in previous studies as holding significant predictive ability. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of daily solar flare occurrence with TSS = 0.65, without any preprocessing to extract features from data. Second, using the attribution methods, we find that the polarity inversion line is an important feature for the deep learning flare forecasting model. Third, the ARs with high Grad-CAM values produce more flares than those with low Grad-CAM values. Fourth, nine SHARP parameters such as total unsigned vertical current, total unsigned current helicity, total unsigned flux, and total photospheric magnetic free energy density are well correlated with Grad-CAM values.

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Thin Film Morphology Control of P3HT:PCBM Organic Solar Cells Using Electrospray Deposition Process

  • Hwang, Won-Tae;Choe, Su-Jeong;Chae, Hui-Yeop
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.432-433
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    • 2012
  • Polymer solar cells are fabricated using electrospray (e-spray) deposition process. It shows comparable performance with reference devices, and has different characteristics according to the thickness of the active layer: In the case of the devices with higher fill factor, it shows relatively lower current density, and vice versa. These films are characterized by atomic force microscopy measurement. The results indicate that the comparable power conversion efficiency made by e-spray results from the 'solvent annealing effect' by process conditions and the different thin film property is caused by the degree of self-organization of the polymer.

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