Browsing by Author "Li, Yat"

Now showing 1 - 4 of 4

Au Nanostructure-Decorated TiO2 Nanowires Exhibiting Photoactivity Across Entire UV-visible Region for Photoelectrochemical Water Splitting
(2013-08-01)
Pu, Ying-Chih
;
Wang, Gongming
;
Chang, Kao-Der
;
Ling, Yichuan
;
Lin, Yin-Kai
Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV-visible region from 300 to 800 nm by manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV visible light for solar fuel production.
Optical Properties and Exciton Dynamics of Alloyed Core/Shell/Shell Cd1-xZnxSe/ZnSe/ZnS Quantum Dots
(2013-04-24)
Fitzmorris, Bob C.
;
Pu, Ying-Chih
;
Cooper, Jason K.
;
Lin, Yi-Fang
;
Hsu, Yung-Jung
In this study we introduce a new method for the onepot synthesis of core/shell/shell alloyed Cd1-xZnxSe/ZnSe/ZnS QDs and examine the effect of the shell coating on the optical properties and exciton dynamics of the alloy core. The photoluminescence (PL) quantum yield is greatly enhanced after shell growth, from 9.6% to 63%. The exciton dynamics were studied by time correlated single photon counting (TCSPC) and fit using integrated singular value decomposition global fitting (i-SVD-GF), which showed the biexponential observed lifetimes on the nanosecond time scale remain the same after shell growth. Using ultrafast transient absorption (TA) spectroscopy and SVD-GF, we have determined that surface passivation by ZnSe and ZnSe/ZnS shells reduces nonradiative recombination primarily on the picosecond time scale. These findings are helpful in directing the development of the next generation of QDs for biological labeling and other applications.
Surface Passivation of TiO2 Nanowires Using a Facile Precursor-Treatment Approach for Photoelectrochemical Water Oxidation
(2014-07-10)
Pu, Ying-Chih
;
Ling, Yichuan
;
Chang, Kao-Der
;
Liu, Chia-Ming
;
Zhang, Jin Z.
We developed a facile precursor-treatment approach for effective surface passivation of rutile TiO2 nanowire photoanode to improve its performance in photoelectrochernical (PEC) water oxidation. The approach was demonstrated by treating rutile TiO2 nanowires with titanium precursor solutions (TiCl4, Ti(OBu)(4), or Ti(OiP)(4)) followed by a postannealing process, which resulted in the additional deposition of anatase TiO2 layer on the nanowire surface. Compared to pristine TiO2, all the precursor-treated TiO2 nanowire electrodes exhibited a significantly enhanced photocurrent density under white light illumination. Among the three precursor-treated samples, Ti(OBu)(4)-treated TiO2 nanowires achieved the largest enhancement of photocurrent generation, which is approximately a 3-fold increase over pristine TiO2. Monochromatic incident photon-to-electron conversion efficiency (IPCE) measurements showed that the improvement of PEC performance was dominated by the enhanced photoactivity of TiO2 in the UV region. The photovoltage and electrochemical impedance spectroscopy (EIS) measurements showed that the enhanced photoactivity can be attributed to the improved charge transfer as a result of effective surface state passivation. This work demonstrates a facile, low-cost, and efficient method for preparing highly photoactive TiO2 nanowire electrodes for PEC water oxidation. This approach could also potentially be used for other photoconversion applications, such as TiO2 based dye-sensitized solar cells, as well as photocatalytic systems.
Surface Passivation of TiO2 Nanowires Using a Facile Precursor-Treatment Approach for Photoelectrochemical Water Oxidation
(2014-07-10)
Pu, Ying-Chih
;
Ling, Yichuan
;
Chang, Kao-Der
;
Liu, Chia-Ming
;
Zhang, Jin Z.
We developed a facile precursor-treatment approach for effective surface passivation of rutile TiO2 nanowire photoanode to improve its performance in photoelectrochernical (PEC) water oxidation. The approach was demonstrated by treating rutile TiO2 nanowires with titanium precursor solutions (TiCl4, Ti(OBu)(4), or Ti(OiP)(4)) followed by a postannealing process, which resulted in the additional deposition of anatase TiO2 layer on the nanowire surface. Compared to pristine TiO2, all the precursor-treated TiO2 nanowire electrodes exhibited a significantly enhanced photocurrent density under white light illumination. Among the three precursor-treated samples, Ti(OBu)(4)-treated TiO2 nanowires achieved the largest enhancement of photocurrent generation, which is approximately a 3-fold increase over pristine TiO2. Monochromatic incident photon-to-electron conversion efficiency (IPCE) measurements showed that the improvement of PEC performance was dominated by the enhanced photoactivity of TiO2 in the UV region. The photovoltage and electrochemical impedance spectroscopy (EIS) measurements showed that the enhanced photoactivity can be attributed to the improved charge transfer as a result of effective surface state passivation. This work demonstrates a facile, low-cost, and efficient method for preparing highly photoactive TiO2 nanowire electrodes for PEC water oxidation. This approach could also potentially be used for other photoconversion applications, such as TiO2 based dye-sensitized solar cells, as well as photocatalytic systems.