Browsing by Author "Chen, Li-Chyong"

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Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes
(2013)
Sun, Chia-Liang
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Pao, Chih-Wen
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Tsai, Huang-Ming
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Chiou, Jau-Wern
;
Ray, Sekhar C.
The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L-3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.
Carbon-doped SnS2 nanostructure as a high-efficiency solar fuel catalyst under visible light
(2018-01-12)
Shown, Indrajit
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Samireddi, Satyanarayana
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Chang, Yu-Chung
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Putikam, Raghunath
;
Chang, Po-Han
Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an L-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS2 (SnS2-C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO2 to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS2 lattice, resulting in different photophysical properties as compared with undoped SnS2. This SnS2-C photocatalyst significantly enhances the CO2 reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS2-C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO2 reduction under visible light, where the in situ carbon-doped SnS2 nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.
Efficient hydrogen production using Cu-based catalysts prepared via homogeneous precipitation
(2009)
Lin, Yu-Kai
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Su, Yi-Han
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Huang, Yun-Hsin
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Hsu, Chia-Jung
;
Hsu, Yu-Kuei
We report here preparation of multi-composition Cu/ZnO/Al(2)O(3) (CZA) catalyst by homogeneous precipitation (HP) method using urea treatment. Compared to the conventional co-precipitation (CP) method, the HP method used here improves the uniformity of metal mixing through homogeneous generation of hydroxide ions as a result of hydrolysis of urea in the solution. In this study, optimization of the conditions to prepare CZA catalyst was achieved by adjusting the urea concentration, amount of water, reaction temperature and reaction time; to control the pH value. The HP-derived CZA particles exhibited a characteristic flower-like morphology with a higher surface area, typically 78.5 m(2)/g as measured by the BET analysis, as compared to the CP-derived CZA catalysts. Induction coupled plasma and energy dispersive spectroscopy mapping results further confirmed the homogeneity of HP-CZA components and highly uniform dispersion of the active metal. Significantly lowering and a narrower range of the reduction temperature for HP-CZA is observed. An improved performance in methanol reforming reaction, in terms of methanol conversion, yield of hydrogen production, and higher carbon dioxide selectivity, has been achieved. Furthermore, the concentration of carbon monoxide can be further reduced by employing CeO(2) and ZrO(2) to modify the support, which also results in reduced reduction temperature and improved performance. Among the modified catalysts, HP-CZCZ catalyst showed the highest methanol conversion and rate of hydrogen production, simultaneously with reduced concentration of CO. Moreover, only 20 mg of catalyst loading yielded 98% methanol conversion rate under more than 8500 h(-1) GHSV. In future, not only can this method be used to synthesize other multi-composition materials with high homogeneity, but also our approach presents opportunity for production of a highly active catalyst for efficient generation of hydrogen for fuel cell applications.
Electrophoretic deposition of PtRu nanoparticles on carbon nanotubes for methanol oxidation
(2009-02-01)
Hsu, Yu-Kuei
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Yang, Ju-Lan
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Lin, Yan-Gu
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Chen, San-Yuan
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Chen, Li-Chyong
Electrophoretic deposition technique was successfully utilized to deposit the PtRu nanoparticles on carbon nanotubes, which were directly grown on carbon cloths (CNTs/CC). We applied an external dc field to drive the PtRu nanoparticles. which were surrounded by negatively charged glycolate in an ethylene glycol process, toward the positively biased CNTs. Systematic studies to achieve optimal size and loading amount by varying the bias potential and deposition time have been carried out. An average PtRu particle size of 2.08 nm with catalytic activity of 1.6 A/cm(2)/mg in electro-oxidation methanol could be achieved, which is highly desirable for fuel cell applications. (C) 2008 Published by Elsevier B.V.
Growth of sparse arrays of narrow GaN nanorods hosting spectrally stable InGaN quantum disks
(2012-07-16)
Chen, Yen-Ting
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Tsai, Wen-Che
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Chen, Wen-Yen
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Hsiao, Ching-Lien
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Hsu, Hsu-Cheng
Wafer-scale production of single InGaN quantum disks (QD) in-a-nanorod array with small rod diameter (> 9 nm) and low rod-density (< 10(8) cm(-2)) has been achieved without extensive processing steps. Excitation power-dependent mu PL spectrum of single QD reveals multi-excitonic peak with 0.75 meV blue-shift for 3 orders of magnitude increasing power, indicating the present system is spectrally stable and nearly free of quantum-confined Stark effects, due possibly to the strain relaxation induced by free surface of small rod diameters. The fully polarized emissions, a high working temperature (180 K), low rod density and good alignment, render this system promising as a potential quantum photon source. (C) 2012 Optical Society of America
Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructures
(2007-12-01)
Huang, Yi-Fan
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Chattopadhyay, Surojit
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Jen, Yi-Jun
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Peng, Cheng-Yu
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Liu, Tze-An
Nature routinely produces nanostructured surfaces with useful properties, such as the self-cleaning lotus leaf, the colour of the butterfly wing, the photoreceptor in brittlestar and the anti-reflection observed in the moth eye. Scientists and engineers have been able to mimic some of these natural structures in the laboratory and in real-world applications. Here, we report a simple aperiodic array of silicon nanotips on a 6-inch wafer with a sub-wavelength structure that can suppress the reflection of light at a range of wavelengths from the ultraviolet, through the visible part of the spectrum, to the terahertz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the silicon result from changes in the refractive index caused by variations in the height of the silicon nanotips, and can be simulated with models that have been used to explain the low reflection from moth eyes. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electro-optical devices for the military.
KSCN-induced Interfacial Dipole in Black TiO2 for Enhanced Photocatalytic CO2 Reduction
(2019-07-17)
Fu, Fang-Yu
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Shown, Indrajit
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Li, Chia-Shuo
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Raghunath, Putikam
;
Lin, Tsai-Yu
Tuning the electronic band structure of black titania to improve photocatalytic performance through conventional band engineering methods has been challenging because of the defect-induced charge carrier and trapping sites. In this study, KSCN-modified hydrogenated nickel nano cluster-modified black TiO2 (SCN-H-Ni-TiO2) exhibits enhanced photocatalytic CO2 reduction due to the interfacial dipole effect. Upon combining the experimental and theoretical simulation approach, the presence of an electrostatic interfacial dipole associated with chemisorption of SCN has dramatic effects on the photocatalyst band structure in SCN H-Ni-TiO2. An interfacial dipole possesses a more negative zeta potential shift of the isoelectric point from 5.20 to 3.20, which will accelerate the charge carrier separation and electron transfer process. Thiocyanate ion passivation on black TiO2 demonstrated an increased work function around 0.60 eV, which was induced by the interracial dipole effect. Overall, the SCN H-Ni-TiO2 photocatalyst showed an enhanced CO2 reduction to solar fuel yield by 2.80 times higher than H-Ni-TiO2 and retained around 88% product formation yield after 40 h.
Label free sub-picomole level DNA detection with Ag nanoparticle decorated Au nanotip arrays as surface enhanced Raman spectroscopy platform
(2011-01-15)
Lo, Hung-Chun
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Hsiung, Hsin-I
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Chattopadhyay, Surojit
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Han, Hsieh-Cheng
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Chen, Chia-Fu
Label free optical sensing of adenine and thymine oligonucleotides has been achieved at the sub-picomole level using self assembled silver nanoparticles (AgNPs) decorated gold nanotip (AuNT) arrays. The platform consisting of the AuNTs not only aids in efficient bio-immobilization, but also packs AgNPs in a three dimensional high surface area workspace, assisting in surface enhanced Raman scattering (SERS). The use of sub-10 nm AgNPs with optimum inter-particle distance ensures amplification of the chemically specific Raman signals of the adsorbed adenine, thymine, cytosine and guanine molecules in SERS experiments. High temporal stability of the Raman signals ensured reliable and repeatable DNA detection even after three weeks of ambient desk-top conservation. This facile architecture, being three dimensional and non-lithographic, differs from conventional SERS platforms. (C) 2010 Elsevier B.V. All rights reserved.
Low-Frequency Contact Noise of GaN Nanowire Device Detected by Cross-Spectrum Technique
(2011-06-01)
Li, Liang-Chen
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Huang, Kuo-Hsun
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Wei, Jia-An
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Suen, Yuen-Wuu
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Liu, Ting-Wei
We report the properties of low-frequency contact noise of multielectrode GaN nanowire (NW) devices. A two-port cross-spectrum technique is used to discriminate the noise of the ohmic contact from that of the NW section. The diameter of the GaN NW is around 100 nm. The Ti/Al electrodes of the NWs are defined by e-beam lithography. The typical resistance of a NW section with a length of 800nm is about 5.5 k Omega and the two-wire resistance is below 100 k Omega. The results show that the low-frequency excess noise of the GaN NW is much smaller than that of the current-flowing contact, indicating that the contact noise dominates the noise behavior in our GaN NW devices. A careful study of the noise amplitude (A) of the 1/f noise of different types of NW and carbon nanotube devices, both in our work and in the literature, yields an empirical formula for estimating A from the two-wire resistance of the device. (C) 2011 The Japan Society of Applied Physics
Luminescence properties of wurtzite AlN nanotips
(2006-10-16)
Shi, Shih-Chen
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Chen, Chia Fu
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Chattopadhyay, Surojit
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Chen, Kuei-Hsien
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Ke, Bo-Wen
The optical properties of aluminum nitride nanotips (AlNNTs) synthesized via vapor transport and condensation process have been studied by cathodoluminescence, photoluminescence (PL), thermoluminescence (TL), and UV absorption measurements. Two defect related transitions around 2.1 and 3.4 eV and an excitonic feature at 6.2 eV were identified. Compared to the AlN macropowders, the AlNNTs showed a blueshift (+0.2 eV) of the similar to 3.2 eV peak. Analysis of both PL and TL excitation measurements indicated the existence of subband gap multiple energy levels in AlNNTs. A significant TL intensity even at 145 degrees C suggests possible ultraviolet detector and dosimetric applications of these AlNNTs. (c) 2006 American Institute of Physics.
Microwave-activated CuO nanotip/ZnO nanorod nanoarchitectures for efficient hydrogen production
(2011)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Chen, Li-Chyong
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Chen, Kuei-Hsien
Microwave treatment of CuO nanotip/ZnO nanorod catalyst precursors has been demonstrated to remarkably enhance their activity in methanol reforming reactions. Studies using XRD, Raman, XPS, XAS, and HRTEM analyses conclude that comparative to conventional heating, microwave treatment significantly enhances the activity and stability of the catalysts, which might be attributed to defect and microstrain formation and strong metal support interaction at the Cu/ZnO interface.
Nanostructured Zinc Oxide Nanorods with Copper Nanoparticles as a Microreformation Catalyst
(2009)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Lin, Yu-Kai
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Chen, Li-Chyong
Ni-Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction
(2018-01-11)
Billo, Tadesse
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Fu, Fang-Yu
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Raghunath, Putikam
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Shown, Indrajit
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Chen, Wei-Fu
One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO2 molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni-nanocluster loaded black TiO2 (Ni/TiO2[Vo]) with built-in dual active sites for selective photocatalytic CO2 conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO2 binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.
O(2) plasma-activated CuO-ZnO inverse opals as high-performance methanol microreformer
(2010-01-01)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Chen, Li-Chyong
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Chen, Kuei-Hsien
We report the use of oxygen vacancy-rich CuO-ZnO inverse opals to strikingly enhance the performance of catalytic methanol reforming reaction with a ratio of 1 : 0.125 : 1 (H(2)O/O(2)/MeOH) at a low reaction temperature of only 230 degrees C, yielding complete conversion of methanol, high hydrogen production rate, ultralow CO formation, and outstanding stability.
O-2 plasma-activated CuO-ZnO inverse opals as high-performance methanol microreformer
(2010-01-01)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Chen, Li-Chyong
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Chen, Kuei-Hsien
We report the use of oxygen vacancy-rich CuO-ZnO inverse opals to strikingly enhance the performance of catalytic methanol reforming reaction with a ratio of 1 : 0.125 : 1 (H2O/O-2/MeOH) at a low reaction temperature of only 230 degrees C, yielding complete conversion of methanol, high hydrogen production rate, ultralow CO formation, and outstanding stability.
On the Reduction of O-2 on Cathode Surfaces of Co-Corrin and Co-Porphyrin: A Computational and Experimental Study on Their Relative Efficiencies in H2O/H2O2 Formation
(2020-02-27)
Huang, Wen-Fei
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Chang, Sun-Tang
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Huang, Hsin-Chih
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Wang, Chen-Hao
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Chen, Li-Chyong
The mechanisms for O-2 reduction and H2P/H2O2 formation on Co-corrin and Co-porphyrin cathode surfaces of the proton exchange membrane fuel cell (PEMFC) systems have been studied by hybrid Hartree-Fock/density functional theory (B3LYP) calculations with the LANL2DZ basis set. The calculations show that the reduced Co-corrin with a single negative charge (Co-corrin(-)) is more reactive than the neutral Co-corrin and the doubly charged Co-corrin(2-). Both O-2 and O adsorptions are most stable on Co-corrin(-), rather than Co-corrin or Co-corrin(2-). The potential energy profiles show that the decomposition of O-2 on both Co-corrin and Co-corrin(-) can take place energetically favorably without thermal activation. The formation of H2O and H2O2 are predicted to occur by two separate reaction paths: the HO path and the HOO path. The HO path with H2O as the predominant product on the reduced Co-corrin(-) surface, the energetically favored surface, under operational cathodic conditions, which is consistent with recent experimental findings, wherein the PEMFCs with pyrolyzed vitamin B12 containing Co-corrin as catalysts loaded at the cathode, can deliver up to 14.5 A cm(-3) at 0.8 V with IR compensation. A similar calculation performed for a Co-porphyrin system shows a significantly less efficient O-2 reduction, consistent with the experiment results of the PEMFC power output studies.
Reversible phase transformation of MnO(2) nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy
(2011-01-01)
Hsu, Yu-Kuei
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Chen, Ying-Chu
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Lin, Yan-Gu
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Chen, Li-Chyong
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Chen, Kuei-Hsien
The reversible phase transformation is reported from hexagonal to monoclinic structure responding to the intercalation/deintercalation of Na(+) between MnO(2) nanosheets upon potential cycling in aqueous electrolyte via an in situ Raman technique. This structural evolution will influence the Na(+) diffusion process in MnO(2) nanosheets and cause phase retention during the self-discharge process.
Reversible phase transformation of MnO2 nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy
(2011-01-01)
Hsu, Yu-Kuei
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Chen, Ying-Chu
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Lin, Yan-Gu
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Chen, Li-Chyong
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Chen, Kuei-Hsien
The reversible phase transformation is reported from hexagonal to monoclinic structure responding to the intercalation/deintercalation of Na+ between MnO2 nanosheets upon potential cycling in aqueous electrolyte via an in situ Raman technique. This structural evolution will influence the Na+ diffusion process in MnO2 nanosheets and cause phase retention during the self-discharge process.
Suppressed piezoelectric polarization in single InGaN/GaN heterostructure nanowires
(2013-10-28)
Tsai, Wen-Che
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Chen, Yen-Ting
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Lin, Chia-Hsien
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Hsu, Wei-Ting
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Hsu, Yung-Sheng
The optical properties of single InGaN/GaN heterostructure nanowires (NWs) with a mean diameter down to 18 nm are investigated. Sharp emission lines originating from the recombination of localized excitons in the InGaN disk layer can be resolved. Excitation-dependent energy shifts, together with spectral diffusions of these emission lines, indicate the presence of a weak quantum confined Stark effect (QCSE) caused by nearby charge fluctuations, rather than the screening of piezoelectric polarizations at the InGaN/GaN interface. The absence of a piezoelectric polarization field is further confirmed by time-resolved photoluminescence measurements. Numerical simulations reveal that the elastic strain relaxation via the NW geometry is marginal and occurs only near the NW sidewalls. Carrier localization preferentially near the periphery of the InGaN disk and alloy intermixing are suggested as possible reasons for the absence of a polarization-induced QCSE in thin InGaN/GaN heterostructure NWs.
Visible-light-driven photocatalytic carbon-doped porous ZnO nanoarchitectures for solar water-splitting
(2012)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, Ying-Chu
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Chen, Li-Chyong
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Chen, San-Yuan
C-doped ZnO hierarchically porous nanoarchitectures were synthesized in situ on indium tin oxide (ITO) through a counter strategy. The PEC performance of the C-doped ZnO nanoarchitectures in the splitting of water without sacrificial reagents was systematically evaluated for the first time. In comparison to other ZnO-based photoanodes in the literature, C-doped ZnO nanoarchitectures exhibit a striking photoresponse. Not only do they have a maximum IPCE value of 95%, but they also have an IPCE at the monochromatic wavelength of 400 nm as high as 26.6%, implying that modification by doping with carbon substantially improves the light utilization and conversion efficiency in the visible region of interest over those obtained using a conventional ZnO structure. This model hybrid photoanode will enable us to design high-activity, high-stability visible-light-driven photoelectrodes in the future.