Browsing by Author "Huang, Wen-Fei"

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CARBON-DOPED TiO2 NANOTUBES: EXPERIMENTAL AND COMPUTATIONAL STUDIES
(2013-05-01)
Huang, Wen-Fei
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Wu, Pin-Jiun
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Hsu, Wei-Chih
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Wu, Chih-Wei
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Liang, K. S.
C-doped TiO2 nanotubes (NTs) with anatase structure, prepared by anodizing the polished Ti foils, were characterized using X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and synchrotron-based X-ray photoemission spectroscopy (XPS). XPS results show electron losses in C atoms, no electron change in Ti atoms, and two doping energy levels appeared in band gaps. Structural geometries, DOSs, PDOSs, and Bader charge analyses of C-doped TiO2 anatase are predicted by periodic DFT calculations. Eight doping positions were taken into consideration: two substitutional cases (in oxygen and titanium sites) and six interstitial cases. We found that the interstitial carbon doping type is the most stable one, whereas the substitutional cases are rather unstable. Band-gap modifications can also be found in oxygen substitution, but not in titanium substitution. Both band-gap modification and non-band-gap modification are found in the interstitial carbon doping. In these eight C-doping systems, only the C atom in the oxygen substitution case gains electrons, 1.14 e, and others present electron losses within 0.5-4.00 e. The results of XPS measurements, DOSs calculations, and Bader charge analyses show that carbon interstitial is the most likely doping type for the C-doped TiO2 NTs.
Computational Investigation of the Adsorption and Reactions of SiHx (x=0-4) on TiO2 Anatase (101) and Rutile (110) Surfaces
(2013-06-15)
Huang, Wen-Fei
;
Chen, Hsin-Tsung
;
Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
The adsorption and reactions of the SiHx (x = 0-4) on Titanium dioxide (TiO2) anatase (101) and rutile (110) surfaces have been studied by using periodic density functional theory in conjunction with the projected augmented wave approach. It is found that SiHx (x = 0-4) can form the monodentate, bidentate, or tridentate adsorbates, depending on the value of x. H coadsorption is found to reduce the stability of SiHx adsorption. Hydrogen migration on the TiO2 surfaces is also discussed for elucidation of the SiHx decomposition mechanism. Comparing adsorption energies, energy barriers, and potential energy profiles on the two TiO2 surfaces, the SiHx decomposition can occur more readily on the rutile (110) surface than on the anatase (101) surface. The results may be used for kinetic simulation of Si thin-film deposition and quantum dot preparation on titania by chemical vapor deposition (CVD), plasma enhanced CVD, or catalytically enhanced CVD. (C) 2013 Wiley Periodicals, Inc.
Computational Study on the Reactions of H(2)O(2) on TiO(2) Anatase (101) and Rutile (110) Surfaces
(2011-04-30)
Huang, Wen-Fei
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Raghunath, P.
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
This study investigates the adsorption and reactions of H(2)O(2) on TiO(2) anatase (101) and rutile (110) surfaces by first-principles calculations based on the density functional theory in conjunction with the projected augmented wave approach, using PW91, PBE, and revPBE functionals. Adsorption mechanisms of H(2)O(2) and its fragments on both surfaces are analyzed. It is found that H(2)O(2), H(2)O, and HO preferentially adsorb at the Ti(5c) site, meanwhile HOO, O, and H preferentially adsorb at the (O(2c))(Ti(5c)), (Ti(5c))(2), and O(2c) sites, respectively. Potential energy profiles of the adsorption processes on both surfaces have been constructed using the nudged elastic band method. The two restructured surfaces, the 1/3 ML oxygen covered TiO(2) and the hydroxylated TiO(2), are produced with the H(2)O(2) dehydration and deoxidation, respectively. The formation of main products, H(2)O(g) and the 1/3 ML oxygen covered TiO(2) surface, is exothermic by 2.8 and 5.0 kcal/mol, requiring energy barriers of 0.8 and 1.1 kcal/mol on the rutile (110) and anatase (101) surface, respectively. The rate constants for the H(2)O(2) dehydration processes have been predicted to be 6.65 x 10(-27) T(4.38) exp(-0.14 kcal mol(-1)/RT) and 3.18 x 10(-23) T(5.60) exp(-2.92 kcal mol(-1)/RT) respectively, in units of cm(3) molecule(-1) s(-1). (C) 2010 Wiley Periodicals, Inc. J Comput Chem 32: 1065-1081, 2011
Computational Study on the Reactions of H2O2 on TiO2 Anatase (101) and Rutile (110) Surfaces
(2011-04-30)
Huang, Wen-Fei
;
Raghunath, P.
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
This study investigates the adsorption and reactions of H2O2 on TiO2 anatase (101) and rutile (110) surfaces by first-principles calculations based on the density functional theory in conjunction with the projected augmented wave approach, using PW91, PBE, and revPBE functionals. Adsorption mechanisms of H2O2 and its fragments on both surfaces are analyzed. It is found that H2O2, H2O, and HO preferentially adsorb at the Ti-5c site, meanwhile HOO, O, and H preferentially adsorb at the (O-2c)(Ti-5c), (Ti-5c)(2), and O-2c sites, respectively. Potential energy profiles of the adsorption processes on both surfaces have been constructed using the nudged elastic band method. The two restructured surfaces, the 1/3 ML oxygen covered TiO2 and the hydroxylated TiO2, are produced with the H2O2 dehydration and deoxidation, respectively. The formation of main products, H2O(g) and the 1/3 ML oxygen covered TiO2 surface, is exothermic by 2.8 and 5.0 kcal/mol, requiring energy barriers of 0.8 and 1.1 kcal/mol on the rutile (110) and anatase (101) surface, respectively. The rate constants for the H2O2 dehydration processes have been predicted to be 6.65 x 10(-27) T-4.38 exp(-0.14 kcal mol(-1)/RT) and 3.18 x 10(-23) T-5.60 exp(-2.92 kcal mol(-1)/RT) respectively, in units of cm(3) molecule(-1) s(-1). (C) 2010 Wiley Periodicals, Inc. J Comput Chem 32: 1065-1081, 2011
Density Functional Theory Study of the Adsorption and Reaction of H(2)S on TiO(2) Rutile (110) and Anatase (101) Surfaces
(2009-11-26)
Huang, Wen-Fei
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
The adsorption and reaction of H(2)S on TiO(2) rutile (110) and anatase (101) surfaces have been investigated by using periodic density functional theory (DFT) in conjunction with the projected augmented wave (PAW) approach. Adsorption mechanisms of H(2)S, HS, and S on both surfaces were analyzed. It was found that H(2)S, HS, S, and H preferentially adsorb at the Ti(5c), O(2c), (Ti(5c))(2), and O(2c) sites, respectively, on the rutile surface, and at the Ti(5c), (Ti(5c))(2), (-O(2c))(-Ti(5c)), and O(2c), sites, respectively, on the anatase surface. Potential energy profiles of the adsorption processes on both Surfaces producing H(2) and H(2)O were constructed using the nudged elastic band (NEB) method. Forming Surface sulfur species by a complete O <-> S exchange at the rutile Surface is endothermic by 15.4 kcal/mol and requires a high energy barrier of 35.5 kcal/mol, while it is endothermic by 5.0 kcal/mol and requires it lower energy barrier of 12.4 kcal/mol at the anatase surface. The rate constants for the dehydrogenation and dehydration processes have been predicted.
Density Functional Theory Study of the Adsorption and Reaction of H2S on TiO2 Rutile (110) and Anatase (101) Surfaces
(2009-11-26)
Huang, Wen-Fei
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Chen, Hsin-Tsung
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Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The adsorption and reaction of H2S on TiO2 rutile (110) and anatase (101) surfaces have been investigated by using periodic density functional theory (DFT) in conjunction with the projected augmented wave (PAW) approach. Adsorption mechanisms of H2S, HS, and S on both surfaces were analyzed. It was found that H2S, HS, S, and H preferentially adsorb at the Ti-5c, O-2c, (Ti-5c)(2), and O-2c sites, respectively, on the rutile surface, and at the Ti-5c, (Ti-5c)(2), (-O-2c)(-Ti-5c), and O-2c, sites, respectively, on the anatase surface. Potential energy profiles of the adsorption processes on both Surfaces producing H-2 and H2O were constructed using the nudged elastic band (NEB) method. Forming Surface sulfur species by a complete O <-> S exchange at the rutile Surface is endothermic by 15.4 kcal/mol and requires a high energy barrier of 35.5 kcal/mol, while it is endothermic by 5.0 kcal/mol and requires it lower energy barrier of 12.4 kcal/mol at the anatase surface. The rate constants for the dehydrogenation and dehydration processes have been predicted.
Mechanisms for reactions of trimethylaluminum with molecular oxygen and water
(2014-05-01)
Nguyen, Hue M. T.
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Tang, Hsin-Yu
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Huang, Wen-Fei
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Lin, M. C.
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應用化學系
(CH3)(3)Al(TMA) has been employed for preparation of various thin films. It is also known to be hypergolic in the air. To unveil the hypergolic phenomenon, the mechanism for the reaction of TMA with O-2 and/or H2O molecules is studied using computational quantum methods. Our results show that TMA reacts with water much faster than with O-2, and water is not an efficient catalyst to help O-2 reacting with TMA. The reactions of TMA with water and oxygen molecules can undergo subsequent ones in the air. However, the barrier predicted for production of CH3 was found to be too high for combustion initiation under the ambient condition. (c) 2014 Elsevier B.V. All rights reserved.
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.
The adsorption and reactions of SiClx (x=0-4) on hydroxylated TiO2 anatase (101) surface: A computational study on the functionalization of titania with Cl2Si(O)O adsorbate
(1970-01-01)
Huang, Wen-Fei
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
"The adsorption and reactions of the SiClx (x = 0-4) on the hydroxylated TiO2 anatase (101) surface have been investigated by using periodic density functional theory calculations in conjunction with the projected augmented wave (PAW) approach. The adsorption and reactions tend to occur more readily on the 'O-w' site derived from water than the 'O-s' site from TiO2 as revealed by the potential energy profiles and adsorption energies. The stepwise reactions of SiClx can be achieved by dehydrochlorination taking place by three paths: Ow-path, cross-path, and O-s-path. The Ow-path is the lowest energy path, in which Cl3Si-O-w(a) and Cl2Si-(O-w)O-w(a) are the main products formed by spontaneous reactions. The ready formation and the high stability of Cl2Si-(O-w)O-w(a) suggest that it can be employed as a molecular linker for Si and other semiconductor quantum dot growth on titania through its high reactivity towards SiHx radicals and metal alkyls, respectively. (C) 2012 Elsevier B.V. All rights reserved."
Vitalizing fuel cells with vitamins: pyrolyzed vitamin B12 as a non-precious catalyst for enhanced oxygen reduction reaction of polymer electrolyte fuel cells
(2012-01-01)
Chang, Sun-Tang
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Wang, Chen-Hao
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Du, He-Yun
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Hsu, Hsin-Cheng
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Kang, Chih-Ming
The limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H-2-O-2 fuel cell using py-B12/C provides a maximum power density of 370 mW cm(-2) and a current density of 0.720 A cm(-2) at 0.5 V at 70 degrees C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.