Browsing by Author "Yang, Chih-Chieh"

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Carbon Nanotube/Nitrogen-Doped Reduced Graphene Oxide Nanocomposites and Their Application in Supercapacitors
(2017-08-01)
Yang, Chih-Chieh
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Tsai, Meng-Han
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Huang, Chun-Wei
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Yen, Po-Jen
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Pan, Chien-Chung
Electrodes of carbon-based nanocomposites with high specific surface areas and suitable pore sizes have high potential for improving power and energy densities of supercapacitors. In this study, nitrogen-doped reduced graphene oxide (NrGO) nanosheets were synthesized to increase the specific surface area of reduced graphene oxide (rGO). The specific surface area of NrGO was increased to 633 m(2)g(-1) compared to that of rGO, 450 m(2)g(-1). A series of NrGO/carbon nanotubes (CNTs) nanocomposites were prepared. By using NrGO/CNTs/polyvinylidene difluoride (PVDF)/carbon black/N-methyl-pyrrolidone (NMP) nanocomposites as both of anode and cathode into two electrodes, such symmetric supercapacitor in the 1 M KOH aqueous electrolyte exhibited high specific capacitance (227 F g(-1) at 20 mV s(-1)), fast rate capability (83% capacitance of current density 1 mA cm(-2) at current density 5 mA cm(-2)), low resistance (0.98 Omega), and excellent cycling stability (87% capacitance retention after 10,000 charge/discharge cycles). Moreover, the symmetric supercapacitor in the ionic liquid (BMIMTFSI) electrolyte possessed a wide operating voltage (3 V) and high energy density (89 Wh kg(-1) at 1 mA cm(-2)). The carbon-based hybrid electrode has high potential for use in energy storage and conversion devices.
Flexible solid-like electrolytes with ultrahigh conductivity and their applications in all-solid-state supercapacitors
(2018-01-01)
Yang, Chih-Chieh
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Lin, Hao-Yang
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Kumar, Amit
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Pattanayak, Bhaskar
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Tsai, Hung-Yi
All-solid-state supercapacitors (ASSS) with solid-state electrolytes (SSEs) can be used to overcome the liquid leakage problem in devices. However, ionic conduction in solid electrolytes is one of the barriers to further improvements in ASSS. This paper describes the fabrication of a flexible SSE composed of poly(vinylidene fluoride-co-hexafluoropropylene), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and ethylene carbonate, which demonstrates an ultrahigh conductivity of 8.52 mS cm(-1) and a wide 5 V operation voltage window of -2 to +3 V. Electrodes composed of active carbon, multiwall carbon nanotubes, and polyvinylidene fluoride were used as both anode and cathode to assemble a symmetrical supercapacitor. The resultant supercapacitor exhibits a maximum power density of 3747 W kg(-1) at an energy density of 7.71 W h kg(-1) and a maximum energy density 17.1 W h kg(-1) at a power density of 630 W kg(-1). It displays excellent cycling stability with 91.3% of the initial specific capacitance after 3000 charging/discharging cycles. This flexible SSE in this study demonstrates a high potential for use in energy storage, conversion, and wearable device applications.
Front vehicle tracking using scene analysis
(2005)
Song, Kai-Tai
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Yang, Chih-Chieh
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電控工程研究所
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Institute of Electrical and Control Engineering
This paper presents a design and implementation of a real-time visual tracking system for vehicle safety applications. A novel feature-based vehicle tracking algorithm is proposed. This algorithm can automatically detect and track multiple moving objects, including cars and motorcycles, ahead of the tracking vehicle. Combined with the concept of focus of expansion (FOE) and scene analysis, the developed system can segment features of moving objects from moving background and provide a collision warning in real time. The proposed algorithm is realized using a CMOS image sensor and Nios embedded processor architecture. The constructed stand-alone visual tracking system has been validated in actual road tests. Experimental results show that the proposed system successfully tracks front vehicles and provides information of collision warning in urban artery with speed around 60 km/hr both at night and day times.
In Situ TEM Investigation of the Electrochemical Behavior in CNTs/MnO2-Based Energy Storage Devices
(2017-09-19)
Tsai, Tsung-Chun
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Huang, Guan-Min
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Yang, Chih-Chieh
Transition metal oxides have attracted much interest owing to their ability to provide high power density in lithium batteries; therefore, it is important to understand the electrochemical behavior and mechanism of lithiation-delithiation processes. In this study, we successfully and directly observed the structural evolution of CNTs/MnO2 during the lithiation process using transmission electron microscopy (TEM). CNTs/MnO2 were selected due to their high surface area and capacitance effect, and the lithiation mechanism of the CNT wall expansion was systematically analyzed. Interestingly, the wall spacings of CNTs/MnO2 and CNTs were obviously expanded by 10.92% and 2.59%, respectively. The MnO2 layer caused structural defects on the CNTs surface that could allow penetration of Li+ and Mn4+ through the tube wall and hence improve the ionic transportation speed. This study provided direct evidence for understanding the role of CNTs/MnO2 in the lithiation process used in lithium ion batteries and also offers potential benefits for applications and development of supercapacitors.
Lithography-free thin-titanium-nanocone metamaterial perfect absorbers using ZnO nanostructures
(2017-10-01)
Lin, Albert
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Parashar, Parag
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Yang, Chih-Chieh
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Jian, Ding Rung
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Huang, Wei-Ming
In this work, thin Ti nanocones are deposited on top of the arrays of ZnO nanopagodas, and the whole structure works as an efficient nanostructured metamaterial perfect absorber (MPA) without using lithography and dry etching. In this design, similar to 1 mu m long ZnO nanopagoda arrays are grown on a 100 nm ZnO buffer layer over the silicon/glass substrate by a treatment with an aqueous solution of L-ascorbic acid. Growth direction and the degree of lamination in the ZnO nanostructures can be easily controlled by adjusting the concentration of L-ascorbic acid. Afterward, these ZnO nanopagodas are coated with a 30nm thin top and a 500nm thick bottom layer of Ti to achieve the proposed nanocone resonant cavity structure with electromagnetic wave field penetration. The overall structure encapsulates three physical concepts, namely, field penetration, adiabatic coupling and cavity resonance, which contribute the broadband perfect absorption. The entire process is carried out at a low temperature (< 90 degrees). We believe the proposed tapered Ti nanocones MPA structure facilitates ultra-broadband perfect spectral absorption with promising nature of low-cost, large-area, and lithography-free. (C) 2017 Optical Society of America
Role of nanorods insertion layer in ZnO-based electrochemical metallization memory cell
(2017-12-01)
Simanjuntak, Firman Mangasa
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Singh, Pragya
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Chandrasekaran, Sridhar
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Lumbantoruan, Franky Juanda
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Yang, Chih-Chieh
An engineering nanorod array in a ZnO-based electrochemical metallization device for nonvolatile memory applications was investigated. A hydrothermally synthesized nanorod layer was inserted into a Cu/ZnO/ITO device structure. Another device was fabricated without nanorods for comparison, and this device demonstrated a diode-like behavior with no switching behavior at a low current compliance (CC). The switching became clear only when the CC was increased to 75 mA. The insertion of a nanorods layer induced switching characteristics at a low operation current and improve the endurance and retention performances. The morphology of the nanorods may control the switching characteristics. A forming-free electrochemical metallization memory device having long switching cycles (> 10(4) cycles) with a sufficient memory window (10(3) times) for data storage application, good switching stability and sufficient retention was successfully fabricated by adjusting the morphology and defect concentration of the inserted nanorod layer. The nanorod layer not only contributed to inducing resistive switching characteristics but also acted as both a switching layer and a cation diffusion control layer.
Role of precursors mixing sequence on the properties of CoMn2O4 cathode materials and their application in pseudocapacitor
(2019-11-14)
Pattanayak, Bhaskar
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Simanjuntak, Firman Mangasa
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Panda, Debashis
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Yang, Chih-Chieh
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Kumar, Amit
In this study, the effect of oxygen vacancy in the CoMn2O4 on pseudocapacitive characteristics was examined, and two tetragonal CoMn2O4 spinel compounds with different oxygen vacancy concentrations and morphologies were synthesized by controlling the mixing sequence of the Co and Mn precursors. The mixing sequence was changed; thus, morphologies were changed from spherical nanoparticles to nanoflakes and oxygen vacancies were increased. Electrochemical studies have revealed that tetragonal CoMn2O4 spinels with a higher number of oxygen vacancies exhibit a higher specific capacitance of 1709 F g(-1) than those with a lower number of oxygen vacancies, which have a higher specific capacitance of 990 F g(-1). Oxygen vacancies create an active site for oxygen ion intercalation. Therefore, oxidation-reduction reactions occur because of the diffusion of oxygen ions at octahedral/tetrahedral crystal edges. The solid-state asymmetric pseudocapacitor exhibits a maximum energy density of 32 Wh.kg(-1) and an excellent cyclic stability of nearly 100%.
SSII cancellation in an EAM-based OFDM-IMDD transmission system employing a novel dynamic chirp model
(2013-01-14)
Hsu, Dar-Zu
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Wei, Chia-Chien
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Chen, Hsing-Yu
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Lu, Yi-Cheng
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Song, Cih-Yuan
We develop a novel subcarrier-to-subcarrier intermixing interference (SSII) cancellation technique to estimate and eliminate SSII. For the first time, the SSII cancellation technique is experimentally demonstrated in an electro-absorption modulator-(EAM-) based intensity-modulation-direct-detection (IMDD) multi-band OFDM transmission system. Since the characteristics of SSII are seriously affected by the chirp parameter, a simple constant chirp model, we found, cannot effectively remove the SSII. Therefore, assuming that the chirp parameter linearly depends on the optical power, a novel dynamic chirp model is developed to obtain better estimation and cancellation of SSII. Compared with 23.6% SSII cancellation by the constant chirp model, our experimental results show that incorporating the dynamic chirp model into the SSII cancellation technique can achieve up to 74.4% SSII cancellation and 2.8-dB sensitivity improvement in a 32.25-Gbps OFDM system over 100-km uncompensated standard single-mode fiber. (C) 2013 Optical Society of America
Templating synthesis of nickel cobaltite nanoflakes and their nanocomposites for making high-performance symmetric supercapacitors
(2019-12-01)
Yang, Chih-Chieh
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Sun, Wen-Chien
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Kumar, Amit
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Pattanayak, Bhaskar
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Tseng, Tseung-Yuen
Nickel cobaltite is one of the most popular pseudocapacitance materials for creating high-performance energy-storage devices because of its low cost, high electric conductivity, excellent electrochemical properties, and environmental friendliness. In this study, nickel cobaltite with nanoneedle morphology was synthesized by adopting the hydrothermal method. Change in the nickel cobaltite from nanoneedle to nanoflake morphology was induced by a template of the surface of a self-assembly graphene oxide (GO)/multiwall carbon nanotube (MWCNT) three-dimensional block matrix. Electrodes fabricated from the nanoflake nickel cobaltite, GO, and MWCNT composite exhibited high specific capacitance of 1525 F g(-1) at a current density of 1 A g(-1) and 1081 F g(-1) at a high current density of 100 A g(-1). When these composite electrodes were used as both the anode and cathode to assemble a symmetric super-capacitor with a 6 M KOH electrolyte, the supercapacitor exhibited a maximum energy density of 25.2 Wh kg(-1) and maximum power density of 5151 Wkg(-1). Moreover, it maintained an excellent cycling stability of 99.6% of the initial capacitance value after 7000 chargeedischarge cycles, demonstrating its remarkable potential for application in energy-storage and conversion devices. (C) 2019 The Author(s). Published by Elsevier Ltd.
The synergistic effect of iron cobaltite compare to its single oxides as cathode in supercapacitor
(1970-01-01)
Saaid, Farish Irfal
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Arsyad, Akmal
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Azman, N. S. H.
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Kumar, Amit
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Yang, Chih-Chieh
Mixed transition metal oxides have attracted great attention in supercapacitors applications due to their better electrochemical performance than their single oxides. In this work, iron cobaltite (FeCo2O4) and its single metal oxides i.e. iron oxide (Fe2O3) and cobalt oxide (Co3O4) were synthesized by a simple hydrothermal process. The structural, spectroscopic and morphological properties were studied using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field-emission scanning electron microscope (FESEM). XRD and FTIR results show the composition of the products. The obtained iron oxide was alpha-Fe2O3. FESEM images show that FeCo2O4 and its single metal oxides exhibit different morphology even though they were synthesized via similar method. The electrochemical properties of the alpha-Fe2O3, Co3O4 and FeCo2O4 electrodes were examined by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) in a 6 M KOH electrolyte solution. At comparable current density, the FeCo2O4 electrode has the highest specific capacitance (C-sp), followed by Co3O4 and alpha-Fe2O3. An asymmetric FeCo2O4/KOH/GO supercapacitor was fabricated. The supercapacitor exhibits maximum energy density of 14.5 Wh kg(-1) and maximum power density of 2177 W kg(-1). It demonstrates 60% rate capability after 1000 continuous charge-discharge cycles at 1 A g(-1).