Gold(Core)–Lead(Shell) Nanoparticle‐Loaded Titanium(IV) Oxide Prepared by Underpotential Photodeposition: Plasmonic Water Oxidation

Underpotential photodeposition of Pb yields an ultrathin shell layer on the Au(111) surface of Au nanoparticle(NP)‐loaded TiO₂ (Au/TiO₂) with heteroepitaxial nanojunctions. The localized surface plasmon resonance of Au/TiO₂ undergoes no damping with the Pb‐shell formation, and the Pb shell offers resistance to aerobic oxidation. Mesoporous films comprising the Au(core)–Pb(shell) NP‐loaded TiO₂ and unmodified Au/TiO₂ were formed on fluorine‐doped tin oxide (FTO) electrode. Using them as the photoanode, photoelectrochemical cells were fabricated, and the photocurrent was measured under illumination of simulated sunlight. The photocurrent for water splitting is dramatically enhanced by the Pb‐shell formation. The photoelectrochemical measurements of the hot‐electron lifetime and density functional theory calculations for model clusters indicate that the Pb‐shell effect originates from the charge separation enhancement.     

Axis‐Oriented,Continuous Anatase Titania Films with Exposed Reactive {100} Facets

Homogeneous TiO₂ single crystals with high exposure of {100} reactive facets were constructed as a seed monolayer on transparent conductive substrates with the desired orientation of reactive facets. A secondary growth process was subsequently carried out on the monolayer seed film to form an axis‐oriented continuous reactive film. Performing secondary growth with different precursors led to optimized conditions for high‐performance photoelectrochemical activity of anatase TiO₂ films. Experimental techniques such as UV/Vis absorption spectroscopy, X‐ray diffraction, high‐resolution SEM, and photoelectrochemistry were used to characterize the structural, optical, and photoelectrochemical properties of the as‐synthesized films. As a photoanode in a photoelectrochemical cell, the axis‐oriented reactive film shows a maximum photocurrent density of 0.3 mA cm^?2, as opposed to 0.075 mA cm^?2 for non‐axis‐oriented (randomly oriented) TiO₂ film.     

Single‐Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO2‐Filmed Ultramicroelectrode

An ultrasensitive photoelectrochemical method for achieving real‐time detection of single nanoparticle collision events is presented. Using a micrometer‐thick nanoparticulate TiO₂‐filmed Au ultra‐microelectrode (TiO₂@Au UME), a sub‐millisecond photocurrent transient was observed for an individual N719‐tagged TiO₂ (N719@TiO₂) nanoparticle and is due to the instantaneous collision process. Owing to a trap‐limited electron diffusion process as the rate‐limiting step, a random three‐dimensional diffusion model was developed to simulate electron transport dynamics in TiO₂ film. The combination of theoretical simulation and high‐resolution photocurrent measurement allow electron‐transfer information of a single N719@TiO₂ nanoparticle to be quantified at single‐molecule accuracy and the electron diffusivity and the electron‐collection efficiency of TiO₂@Au UME to be estimated. This method provides a test for studies of photoinduced electron transfer at the single‐nanoparticle level.     

Photocurrent Enhancement of Dye‐Sensitized Solar Cells owing to Increased Dye‐Adsorption onto Silicon‐Nanoparticle‐Coated Titanium‐Dioxide Films

The inverse‐micellar preparation of Si nanoparticles (Nps) was improved by utilizing sodium naphthalide. The Si Nps were subsequently functionalized with 4‐vinylbenzoic acid for their attachment onto TiO₂ films of dye‐sensitized solar cells (DSSCs). The average diameter of the COOH‐functionalized Si (Si? COOH) Nps was 4.6(±1.7) nm. Depth profiling by secondary‐ion mass spectrometry revealed that the Si Nps were uniformly attached onto the TiO₂ films. The number of Ru^II dye molecules adsorbed onto a TiO₂ film that was treated with the Si? COOH Nps was 42 % higher than that on the untreated TiO₂ film. As a result, DSSCs that incorporated the Si? COOH Nps exhibited higher short‐circuit photocurrent density and an overall energy‐conversion efficiency than the untreated DSSCs by 22 % and 27 %, respectively. This enhanced performance, mostly owing to the intramolecular charge‐transfer to TiO₂ from the dye molecules that were anchored to the Si? COOH Nps, was confirmed by comparing the performance with two different Ru^II–bipyridine dyes (N719 and N749).     

Multiple plasmonic effect on photocurrent generation of metal‐loaded titanium dioxide composite/dye films on gold grating surface

We demonstrate the multiple plasmonic effect on the photocurrent properties of photoanodes containing Ag or Au nanoparticles (NPs) loaded onto titanium dioxide film (Ag–TiO₂ or Au–TiO₂) on Au grating surfaces. Ag–TiO₂ or Au–TiO₂ nanocomposite particles are prepared by a flame spray pyrolysis route. The structures and morphologies of the prepared products are characterized by high‐resolution transmission electron microscopy. The Ag–TiO₂ or Au–TiO₂ composite NPs are deposited by spin coating onto the Au grating surfaces. The photoanode electrode is a layered structure of blu‐ray disc‐recordable grating substrate/Au/Ag (or Au)–TiO₂/dye/electrolyte/indium‐tin oxide. The plasmonic effect is induced when Ag or Au NPs are located within the propagating surface plasmon (SP) field on the Au grating surface. The short‐circuit photocurrent is increased by exciting the grating‐coupled propagating SP on the Au gratings and is further enhanced by positioning the Ag or Au NPs within the grating‐coupled SP field. Copyright © 2014 John Wiley & Sons, Ltd.     

One‐Pot Synthesis of Nitrogen‐doped TiO2 Nanowires with Enhanced Photocurrent Generation

A nitrogen‐doped TiO₂ (N‐TiO₂) nanowire film was synthesized via a one‐pot hydrothermal method using triethylamine as nitrogen source. The effect of the concentration of the triethylamine on the films was evaluated. In addition, the N‐TiO₂ nanowires were characterized using field‐emission scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and ultraviolet–visible spectroscopy. A 3.2× enhancement of the photocurrent for N‐TiO₂ (0.6) was achieved over the as‐prepared TiO₂ nanowire, under AM1.5G solar illumination. This was due to nitrogen doping, which could narrow the bandgap of titania to extend the adsorption of the catalyst to the visible light region.     

Single‐Nanoparticle Collision Events: Tunneling Electron Transfer on a Titanium Dioxide Passivated n‐Silicon Electrode

Single‐nanoparticle collisions were observed on an n‐type silicon electrode (600 μm diameter) passivated by a thin layer of amorphous TiO₂, where the current steps occurred by tunneling electron transfer. The observed collision frequency was in reasonable agreement with that predicted from theory. The isolated electrode, after a collision experiment, with a Pt/TiO₂/n‐Si architecture was shown to retain the photoelectrochemical properties of n‐Si without photocorrosion or current decay. The Pt/TiO₂/n‐Si electrode produced 19 mA cm^?2 of photocurrent density under 100 mW cm^?2 irradiation from a xenon lamp during oxygen evolution without current fading for over 12 h.     

掺杂纳米金粒子的火焰氧化TiO2膜的光电化学性质的研究

A nano-Au modified TiO2 electrode was prepared via the oxidation of Ti sheet in flame and subsequent modification with gold nanoparticles. The results of SEM and TEM measurements show that the Au nanoparticles are well dispersed on TiO2 surface. A near 2-fold enhancement in photocurrent was achieved upon the modification with Au nanoparticles. From the results of photocurrent and electrochemical impedance experiments it was found that the flatband potential of nano-Au/TiO2 electrode negatively shifted about 100 mV in 0.5 mol/L Na2SO4 solutions compared with that of bare TiO2 electrode. The improvement of photoelectrochemical performance was explained by the inhibition for charge recombination of photo-induced electrons and holes, and the promotion for interracial charge-transfer kinetics at nano-Au/TiO2 composite film. Such nanometal-semiconductor composite films have the potential application in improving the performance of photoelectrochemical solar cells.     

Enhancing the Performance of Dye‐Sensitized Solar Cells with a Gold‐Nanoflowers Box

To improve the electron collection, electron lifetime, and light‐harvesting efficiency of dye‐sensitized solar cells simultaneously, Au nanoflowers were prepared and used to cover the entire TiO₂ film. Deposition of Au nanoflowers around the TiO₂ film formed a light‐scattering “box” that covered the entire TiO₂ film. Compared with a light‐scattering layer that only covers the top surface of TiO₂, the Au‐nanoflowers box exhibited better light‐harvesting efficiency due to omnidirectional light scattering, faster electron transport (attributed to the formation of electron channels between the metallic Au nanoflowers and the electron‐collection electrode), and slower charge recombination. As a consequence, the short‐circuit photocurrent and open‐circuit photovoltage were both enhanced significantly, which improved the power conversion efficiency from 8.12 to 10.91 % (34 %) when an Au‐nanoflowers box was wrapped around the photoanode.     

Synthesis of Hollow Mesoporous TiO2 Microspheres with Single and Double Au Nanoparticle Layers for Enhanced Visible‐Light Photocatalysis

A facile method was used to prepare hollow mesoporous TiO₂ and Au@TiO₂ spheres using polystyrene (PS) templates. Au nanoparticles (NPs) were simultaneously synthesized and attached on the surface of PS spheres by reducing AuCl₄^? ions using sodium citrate which resulted in the uniform deposition of Au NPs. The outer coating of titania via sol‐gel produced PS@Au@TiO₂ core–shell spheres. Removing the templates from these core–shell spheres through calcination produced hollow mesoporous and crystalline Au@TiO₂ spheres with Au NPs inside the TiO₂ shell in a single step. Anatase spheres with double Au NPs layers, one inside and another outside of TiO₂ shell, were also prepared. Different characterization techniques indicated the hollow mesoporous and crystalline morphology of the prepared spheres with Au NPs. Hollow anatase spheres with Au NPs indicated enhanced harvesting of visible light and therefore demonstrated efficient catalytic activity toward the degradation of organic dyes under the irradiation of visible light as compared to bare TiO₂ spheres.     

Photosensitization of TiO2 nanoparticulate thin film electrodes by CdS nanoparticles

Surface photovoltage spectra (SPS) measurements of TiO₂ show that a large surface state density is present on the TiO₂ nanoparticles and these surface states can be efficiently decreased by sensitization using CdS nanoparticles as well as by suitable heat treatment. The photoelectrochemical behavior of the bare TiO₂ thin film indicates that the mechanism of photoelectron transport is controlled by the trapping/detrapping properties of surface states within the thin films. The slow photocurrent response upon the illumination can be explained by the trap saturation effect. For a TiO₂ nanoparticulate thin film sensitized using CdS nanoparticles, the slow photocurrent response disappears and the steady-state photocurrent increases drastically, which suggests that photosensitization can decrease the effect of surface states on photocurrent response. Electronic Publication     

Photoelectrochemical Complexes of Fucoxanthin‐Chlorophyll Protein for Bio‐Photovoltaic Conversion with a High Open‐Circuit Photovoltage

Open‐circuit photovoltage (V_oc ) is among the critical parameters for achieving an efficient light‐to‐charge conversion in existing solar photovoltaic devices. Natural photosynthesis exploits light‐harvesting chlorophyll (Chl) protein complexes to transfer sunlight energy efficiently. We describe the exploitation of photosynthetic fucoxanthin‐chlorophyll protein (FCP) complexes for realizing photoelectrochemical cells with a high V_oc . An antenna‐dependent photocurrent response and a V_oc up to 0.72 V are observed and demonstrated in the bio‐photovoltaic devices fabricated with photosynthetic FCP complexes and TiO₂ nanostructures. Such high V_oc is determined by fucoxanthin in FCP complexes, and is rarely found in photoelectrochemical cells with other natural light‐harvesting antenna. We think that the FCP‐based bio‐photovoltaic conversion will provide an opportunity to fabricate environmental benign photoelectrochemical cells with high V_oc , and also help improve the understanding of the essential physics behind the light‐to‐charge conversion in photosynthetic complexes.     

Treatment of TiO2 with COOH‐Functionalized Germanium Nanoparticles to Enhance the Photocurrent of Dye‐Sensitized Solar Cells

A dye‐sensitized solar cell (DSSC) containing a TiO₂ film treated with COOH‐functionalized germanium nanoparticles (Ge COOH Nps) exhibited a higher short‐circuit photocurrent density (J_sc; 15.4 mA cm⁻²) compared to the corresponding untreated DSSC (13.4 mA cm⁻²) using N719 and a 12 μm thick TiO₂ film at 100 mW cm⁻². The amount of N719 attached to the treated TiO₂ film was 21 % greater than that attached to the untreated TiO₂ film. Enhancement of the J_sc value by 15 % was attributed mostly to an intramolecular charge transfer from N719 attached to the Ge COOH Nps to the TiO₂ conduction band through the Ge COOH Nps.     

Photocurrent Response of Surface‐Functionalized Metal Oxides with Well‐Matched Energy Levels: From Nothing to Something

In recent years, an enormous amount of research has been devoted to the study of photosensitive materials from both fundamental and practical viewpoints, due to their wide applications in photocatalytic 1 – 3 and optoelectronic devices, 4 , 5 ultraviolet (UV) photodetectors, 6 – 9 photoswitch microdevices, 10 , 11 light‐emitting diodes, 12 , 13 photovoltaic devices, 14 – 16 and photoelectrochemical cells. 17 Metal oxides, such as ZnO, TiO₂, SnO₂, and NiO have been the most investigated photosensitive materials. 3 , 6 – 8 , 18 – 21 To enhance and take full advantage of their photosensitivity, functionalizing their surface with a polymer that has a high light absorption ability has become one of the widely used methods. 1 – 12 , 22 – 24 For example, Z. L. Wang et al. reported that the UV photocurrent of a ZnO nanobelt‐based sensor was enhanced by close to five orders of magnitude after functionalizing its surface with polystyrene sulfate which has a high UV absorption ability. 25 T. Sasaki et al. reported the assembly of a TiO₂ nanoparticle film with poly(3,4‐ethylenedioxythiophene) and poly(4‐styrene sulfonate) (PEDOT‐PSS) through layer‐by‐layer fabrication in the nanometer scale. The electric conductivity of the TiO₂ composite films could be tuned by UV and visible (Vis) light. 22 Thus, sunlight or photon energy can be used and transformed to electrical energy by UV‐photosensitive metal oxides after their surfaces have been functionalized with a dye that has a high Vis absorption ability. To date, most of the dye‐sensitized solar cells are based on the surface functionalization of UV‐photosensitive metal oxides by dyes. 26 – 28 However, to the best of our knowledge, all of the reports on surface functionalization enhanced only the UV photosensitivity of the metal oxide. In other words, this method has been used exclusively to enhance the UV photocurrent in metal oxides that already have UV‐photosensitive properties, but not to induce UV photocurrent in metal oxides that have no UV‐photosensitive properties. In fact, to the best of our knowledge, there are no surface‐functionalizing reports on inducing UV or Vis photocurrent in metal oxides that have no UV‐ or Vis‐photosensitive properties.     

Structural and photoelectrochemical characterization of MWCNT-TiO2 matrices sensitized with Bi2S3

Structural and photoelectrochemical characterization of multiwall carbon nanotubes–titanium oxide (MWCNT-TiO₂) matrices, sensitized with bismuth sulfide (Bi₂S₃), are presented as a function of MWCNT-TiO₂ annealing temperature and Bi₂S₃ deposition time. Random matrices of multiwall carbon nanotubes were grown on stainless steel substrates by spray pyrolysis and then functionalized with a thin layer of TiO₂. Air annealing modifies the morphology and C/TiO₂ ratio in the hybrid materials, from MWCNT-TiO₂ core and shell structures at 400 °C to carbon-doped TiO₂ (C-TiO₂) at 550 °C. Both matrices increase the amount of Bi₂S₃ deposited by the chemical bath, but the best photoelectrochemical performance is observed in electrodes based on C-TiO₂. Electrodes based on core–shell structures of MWCNT-TiO₂ show large capacitive currents that interfere with photocurrent generation, demonstrating the storage potential of MWCNT and the critical role of MWCNT/TiO₂ ratio for photoelectrochemical applications. Regardless of the superior properties of C-TiO₂ photoanodes, the power conversion efficiency of Bi₂S₃-sensitized C-TiO₂ is limited by the appearance of an electron collection barrier at the substrate/film interface.     

Sensitization of Mn with CdS nanoparticles via electrochemical deposition technique for photocurrent enhancement of nanomaterial’s-sensitized photoelectrochemical cells

A photoconversion efficiency of 2.12% was obtained under visible light illumination by nanostructure-sensitized photoelectrochemical cells using Mn/CdS as sensitizer loaded on TiO₂ nanotube arrays (NTAs) (Mn/CdS/TiO₂). Sensitization of Mn on CdS nanoparticles pre-loaded on TiO₂ NTAs was carried out by a two-step electrodeposition method. Compared with unsensitized TiO₂ NTAs, the photocurrent had increased from 0.03 to 4.12 for Mn/CdS/TiO₂ prepared at 1 min. The effects of deposited Mn on the physical, chemical, and photoelectrochemical properties of the CdS/TiO₂ NTAs nanostructure were investigated by using UV–visible diffuse reflectance spectroscopy, X-ray diffractometry, and field-emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photoelectrochemical analysis was examined in a three-electrode system under a halogen illumination by using the prepared film as the photo-anode.     

Toward Cost‐Effective Manufacturing of Silicon Solar Cells: Electrodeposition of High‐Quality Si Films in a CaCl2‐based Molten Salt

Electrodeposition of Si films from a Si‐containing electrolyte is a cost‐effective approach for the manufacturing of solar cells. Proposals relying on fluoride‐based molten salts have suffered from low product quality due to difficulties in impurity control. Here we demonstrate the successful electrodeposition of high‐quality Si films from a CaCl₂‐based molten salt. Soluble Si^IV−O anions generated from solid SiO₂ are electrodeposited onto a graphite substrate to form a dense film of crystalline Si. Impurities in the deposited Si film are controlled at low concentrations (both B and P are less than 1 ppm). In the photoelectrochemical measurements, the film shows p‐type semiconductor character and large photocurrent. A p–n junction fabricated from the deposited Si film exhibits clear photovoltaic effects. This study represents the first step to the ultimate goal of developing a cost‐effective manufacturing process for Si solar cells based on electrodeposition.     

A facile strategy to modify TiO2 nanoparticles via surface‐initiated ATRP of styrene

A core‐shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (n‐TiO₂) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface‐initiated atom transfer radical polymerization (ATRP) at 90 °C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, ¹H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core‐shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO₂‐PS nanocomposites exhibited higher glass transition temperature (T_g) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface‐attached polymers were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1782–1790, 2010     

Synthesis and Study of Plasmon‐Induced Carrier Behavior at Ag/TiO2 Nanowires

Nanocomposites of Ag/TiO₂ nanowires with enhanced photoelectrochemical performance have been prepared by a facile solvothermal synthesis of TiO₂ nanowires and subsequent photoreduction of Ag⁺ ions to Ag nanoparticles (AgNPs) on the TiO₂ nanowires. The as‐prepared nanocomposites exhibited significantly improved cathodic photocurrent responses under visible‐light illumination, which is attributed to the local electric field enhancement of plasmon resonance effect near the TiO₂ surface rather than by the direct transfer of charge between the two materials. The visible‐light‐driven photocatalytic performance of these nanocomposites in the degradation of methylene blue dye was also studied, and the observed improvement in photocatalytic activity is associated with the extended light absorption range and efficient charge separation due to surface plasmon resonance effect of AgNPs.     

Interim Anatase Coating Layer Stabilizes Rutile@CrxOy Photoanode for Visible‐Light‐Driven Water Oxidation

Ternary core–shell heterostructured rutile@anatase@Cr_xO_y nanorod arrays were elaborately designed as photoanodes for efficient photoelectrochemical water splitting under visible‐light illumination. The four‐fold enhanced and stabilized visible‐light photocurrent highlights the unique role of the interim anatase layer in accelerating the interfacial charge transfer from the Cr_xO_y chromophore to rutile nanorods.