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.

We demonstrated for the first time that Agnanoparticle-decorated SiO 2 nanospheres (NSs) may display noticeable photocatalytic activities upon surface plasmon resonance (SPR) excitation. The samples were prepared by reacting SiO 2 NSs with AgNO 3 in the seed-mediated growth process, from which the Ag particle size and decoration density can be readily controlled. The dependence of the SPR-mediated photocatalytic performance of Ag-decorated SiO 2 NSs on the Ag morphology was investigated and presented. The as-prepared Agdecorated SiO 2 NSs showed a significantly red shifted and relatively broad SPR absorption when compared with the individually dispersed Ag nanoparticles. Owing to the considerably broad SPR absorption that spanned from the visible to the near-infrared region, Ag-decorated SiO 2 NSs surpassed N-doped P-25 TiO 2 powder and individually dispersed Ag nanoparticles in photocatalytic activity, demonstrating their potential as an active photocatalyst in nearly all the current photocatalysis applications. Furthermore, the result of performance evaluation under natural sunlight shows that the present Ag-decorated SiO 2 NSs can be used as highly efficient photocatalysts that may practically harvest energy from sunlight. The current study provides a new paradigm for designing plasmonic metal nanostructures that can effectively absorb the entire solar spectrum and beyond for solar fuel generation.

Correlations among Au content, SPR-mediated charge transfer and electromagnetic response, and the resultant photoactivity enhancement for ZnO–Au nanocrystals were established.

We developed a facile precursor-treatment approach for effective surface passivation of rutile TiO 2 nanowire photoanode to improve its performance in photoelectrochemical (PEC) water oxidation. The approach was demonstrated by treating rutile TiO 2 nanowires with titanium precursor solutions (TiCl 4 , Ti(OBu) 4 , or Ti(OiP) 4 ) followed by a post annealing process, which resulted in the additional deposition of anatase TiO 2 layer on the nanowire surface. Compared to pristine TiO 2 , all the precursor-treated TiO 2 nanowire electrodes exhibited a significantly enhanced photocurrent density under white light illumination. Among the three precursor-treated samples, Ti(OBu) 4 -treated TiO 2 nanowires achieved the largest enhancement of photocurrent generation, which is approximately a 3-fold increase over pristine TiO 2 . Monochromatic incident photon-to-electron conversion efficiency (IPCE) measurements showed that the improvement of PEC performance was dominated by the enhanced photoactivity of TiO 2 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 TiO 2 nanowire electrodes for PEC water oxidation. This approach could also potentially be used for other photoconversion applications, such as TiO 2 based dyesensitized solar cells, as well as photocatalytic systems. electrodes were 0.039, 0.081, 0.043 and 0.045 mole/cm 2 , respectively. This result signified that the apparent surface area of the TiO 2 -TIP and TiO 2 -TBU electrodes were equivalent to that of the pristine TiO 2 electrode, while the TiO 2 -TCL electrode with rough surface had approximately twice the surface area of the pristine TiO 2 . This phenomenon further supported that the improved PEC performance of the TiO 2 -TIP and TiO 2 -TBU electrodes was related to effective surface passivation rather than an increase in surface area. As for the TiO 2 -TCL electrode, the improved PEC performance could be partly ascribed to the surface area effect because the increase in surface area was evident. Figure 5. (a) Absorption spectra for pristine TiO 2 and precursor-treated TiO 2 nanowire array films. (b) Absorption spectra for the N3-adsorbed samples after they were immersed into a base solution for N3 desorption. Inset shows the corresponding apparent color of the samples.