Browsing by Author "Wu, Feng-Yu"

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Direct conversion of multilayer molybdenum trioxide to nanorods as multifunctional electrodes in lithium-ion batteries
(2014)
Ibrahem, Mohammed Aziz
;
Wu, Feng-Yu
;
Mengistie, Desalegn Alemu
;
Chang, Chia-Seng
;
Li, Lain-Jong
In this study we prepared molybdenum trioxide (MoO3) nanorods having average lengths of 0.5-1.5 mu m and widths of approximately 100-200 nm through a one-step mechanical break-down process involving favorable fracturing along the crystal direction. We controlled the dimensions of the as-prepared nanorods by applying various imposing times (15-90 min). The nanorods prepared over a reaction time of 90 min were, on average, much shorter and narrower relative to those obtained over 30 min. Evaluations of lithium-ion storage properties revealed that the electrochemical performance of these nanorods was much better than that of bulk materials. As cathodes, the nanorods could deliver a high specific capacity (>315 mA h g(-1)) with losses of less than 2% in the first cycle at a rate of 30 mA g(-1); as anodes, the specific capacity was 800 mA h g(-1) at a rate of 50 mA g(-1). Relative to alpha-MoO3 microparticles, these nanorods displayed significantly enhanced lithium-ion storage properties with higher reversible capacities and better rate performance, presumably because their much shorter diffusion lengths and higher specific surface areas allowed more-efficient insertion/deinsertion of lithium ions during the charge/discharge process. Accordingly, enhanced physical and/or chemical properties can be obtained through appropriate nanostructuring of materials.
High-performance graphene/sulphur electrodes for flexible Li-ion batteries using the low-temperature spraying method
(2015-01-01)
Kumar, Pushpendra
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Wu, Feng-Yu
;
Hu, Lung-Hao
;
Abbas, Syed Ali
;
Ming, Jun
Elementary sulphur (S) has been shown to be an excellent cathode material in energy storage devices such as Li-S batteries owing to its very high capacity. The major challenges associated with the sulphur cathodes are structural degradation, poor cycling performance and instability of the solid-electrolyte interphase caused by the dissolution of polysulfides during cycling. Tremendous efforts made by others have demonstrated that encapsulation of S materials improves their cycling performance. To make this approach practical for large scale applications, the use of low-cost technology and materials has become a crucial and new focus of S-based Li-ion batteries. Herein, we propose to use a low temperature spraying process to fabricate graphene/S electrode material, where the ink is composed of graphene flakes and the micron-sized S particles prepared by grinding of low-cost S powders. The S particles are found to be well hosted by highly conductive graphene flakes and consequently superior cyclability (similar to 70% capacity retention after 250 cycles), good coulombic efficiency (similar to 98%) and high capacity (similar to 1500 mA h g(-1)) are obtained. The proposed approach does not require high temperature annealing or baking; hence, another great advantage is to make flexible Li-ion batteries. We have also demonstrated two types of flexible batteries using sprayed graphene/S electrodes.
Improving the Light Trapping Efficiency of Plasmonic Polymer Solar Cells through Photon Management
(2012-10-04)
Hsiao, Yu-Sheng
;
Charan, Shobhit
;
Wu, Feng-Yu
;
Chien, Fan-Ching
;
Chu, Chih-Wei
In this study, we have explored how light trapping efficiency can be enhanced by using gold nanoparticles (Au NPs) of various sizes and shapes on the front of polymer solar cells (PSCs) with the active layer-blends of poly(3-hexyl thiophene) and [6,6]-phenyl-C-61-butyric acid methyl ester. The light-concentrating behavior was enhanced after we had incorporated gold nanospheres or nanorods into the anodic buffer layer [based on poly(3,4-ethylenedioxythiophene):polystyrenesulfonate] to trigger various localized surface plasmon resonance (LSPR) bands. Comparison of the optical characteristics and the performance of the PSCs prepared with and without Au NPs, and we found that the UV-vis and wavelength-dependent photoluminescent spectral data corroborated with the device performance due to the photon management by considering the light scattering and LSPR effects at the active layer. The presence of Au NPs increased the power conversion efficiency to approximately 4.3% (an enhancement of 24%).
Improving the Light Trapping Efficiency of Plasmonic Polymer Solar Cells through Photon Management
(2012-10-04)
Hsiao, Yu-Sheng
;
Charan, Shobhit
;
Wu, Feng-Yu
;
Chien, Fan-Ching
;
Chu, Chih-Wei
In this study, we have explored how light trapping efficiency can be enhanced by using gold nanoparticles (Au NPs) of various sizes and shapes on the front of polymer solar cells (PSCs) with the active layer-blends of poly(3-hexyl thiophene) and [6,6]-phenyl-C-61-butyric acid methyl ester. The light-concentrating behavior was enhanced after we had incorporated gold nanospheres or nanorods into the anodic buffer layer [based on poly(3,4-ethylenedioxythiophene):polystyrenesulfonate] to trigger various localized surface plasmon resonance (LSPR) bands. Comparison of the optical characteristics and the performance of the PSCs prepared with and without Au NPs, and we found that the UV-vis and wavelength-dependent photoluminescent spectral data corroborated with the device performance due to the photon management by considering the light scattering and LSPR effects at the active layer. The presence of Au NPs increased the power conversion efficiency to approximately 4.3% (an enhancement of 24%).
Three- Dimensional Molybdenum Sulfi de Sponges for Electrocatalytic Water Splitting
(2014-03-01)
Chang, Yung-Huang
;
Wu, Feng-Yu
;
Chen, Tzu-Yin
;
Hsu, Chang-Lung
;
Chen, Chang-Hsiao