Array Photoelectrode Research Articles

Molybdenum-doped and anatase/rutile mixed-phase TiO2 nanotube photoelectrode for high photoelectrochemical performance

Molybdenum-doped TiO2 nanotube arrays (Mo-doped TiO2 NTs) photoelectrodes with anatase/rutile mixed phase are successfully fabricated via two-step anodization of titanium followed by a hydrothermal doping treatment process. The Mo-doped TiO2 NT material shows higher photocurrent density and enhanced incident photon to current conversion efficiency (IPCE) compared with the pristine TiO2 NTs for photoelectrochemical (PEC) water-splitting. The improvement of PEC response results from not only the increasing of oxygen vacancies and reducing of the recombination of photoexcited charges by Mo-doping, but also the new formed heterojunctions of anatase/rutile mixed-phase by hydrothermal treatment. Moreover, the Mo-doped TiO2 NTs show high stability and obvious visible absorption with considerable photocurrent density under visible light (λ > 420 nm).

High-performance CdS–ZnS core–shell nanorod array photoelectrode for photoelectrochemical hydrogen generation

High-performance CdS–ZnS core–shell nanorod array photoelectrode for photoelectrochemical hydrogen generation from water.

Achieving Enhanced Dye‐Sensitized Solar Cell Performance by TiCl4/Al2O3 Doped TiO2 Nanotube Array Photoelectrodes

For various reasons, low cost, easy fabrication, and so forth, dye‐sensitized solar cells (DSSCs) have been consistently studied in many laboratories. To improve the DSSCs performance, using an aqueous solution of titanium tetrachloride (TiCl4) treatment is one of many processes. Before the treatment of TiCl4, nanoporous TiO2 nanotubes (TNTs) are fabricated through a secondary anodization process. TiCl4 treatment on TNTs film enhanced short‐circuit current density (JSC) and aluminum oxide (Al2O3) posttreatment enhanced open‐circuit voltage (VOC). As a result, Al2O3 posttreatment on TNTs film conversion efficiency of 8.65% is realized, which is 7% higher than TiCl4 treatment on TNTs film. In this work, we investigated that double dip‐coating of TiCl4/Al2O3 treatment on TiO2 nanotubes film had an effect on enhancement of JSC and VOC due to improvement of electron transfer, increment of dye adsorption, and reduction of recombination rate of charge. Photoelectrode DSSCs with light‐to‐electric energy conversion efficiency were achieved under a simulated solar light irradiation of 100 mW·cm2 (AM 1.5).

Heterojunction Engineering of CdS and Ag2S Quantum Dots Co-Sensitized TiO2 Nanotube Array Photoelectrode

CdS and Ag2S heteojunctions sensitized TiO2 nanotube arrays (TiO2 NTs/CdS-Ag2S) were prepared by cation exchange between Cd2+ and Ag+ on the basis of the TiO2 NTs/CdS. The deposition of CdS and Ag2S heteojunctions on the upper and inner surface of the TiO2 NTs was confirmed by field emission scanning electron (FE-SEM) and transmission electron microscopes (TEM). The UV-vis spectrum of the TiO2 NTs/CdS-Ag2S revealed the photoresponse range covering the full visible and near-infrared regions, and showed considerable enhanced photoelectrochemical properties. The corresponding charge transfer path of the TiO2 NTs/CdS-Ag2S photoelectrode was also illuminated.

Photoelectrochemical label-free immunoassay of octachlorostyrene based on heterogeneous CdSe/CdS/Pt/TiO2 nanotube array

A novel heterogeneous CdSe/CdS/Pt/TiO2 nanotube array photoelectrode (denoted as CdSe/CdS/Pt/TiO2 NTA) was developed by dipping and deposition technique as well as successive ionic layer adsorption and reaction (SILAR). An octachlorostyrene (OCS) photoelectrochemical immunosensor was constructed by cross-linking anti-OCS antibody onto the CdSe/CdS/Pt/TiO2 NTA using anti-OCS antibody prepared in this laboratory. The as-prepared photoelectrochemical immunosensor is highly stable, sensitive and selective to octachlorostyrene with a limit of detection (LOD) of 2.08pM and a linear range from 0.1 to 10μM. The practical application of the photoelectrochemical immunosensor is also realized in the selective determination of octachlorostyrene in sewage sample.

Preparation and photocatalytic properties of graphene/TiO2 nanotube arrays photoelectrodes

Graphene/TiO2 Nanotube Arrays (GR/TNAs) photoelectrodes were fabricated by in-situ anodization and electro-deposition method. The surface morphology, structure, photoluminescence spectra (PL), and photocatalytic activity of the samples were investigated. The as-prepared graphene/TNAs (GR/TNAs) photoelectrodes showed significant improvement in the separation of photogenerated carriers and excellent photocatalytic stability. The effects of irradiation time, initial concentration, ionic strength and bias potential on the removal of rhodamine B (Rh.B) by TNAs and GR/TNAs were studied. Results showed that degradation rate of Rh.B for GR/TNAs photoelectrodes reached 75% after 60min illumination at pH of 6.0. The GR/TNAs exhibited significantly enhanced photocatalytic activity compared to unmodified TNAs. When the bias potential was applied, Rh.B degradation rate increased to 90% at 0.5V. NO3−, Ca2+ and Mg2+ in the solution promoted the degradation of Rh.B, while SO42−, Cl− and F− suppressed the removal rate.

A family of vertically aligned nanowires with smooth, hierarchical and hyperbranched architectures for efficient energy conversion

A powerful full solution-based process was demonstrated to synthesize various vertically aligned TiO2 wires/rods self-assembled arrays nanostructures on conductive substrates via a simple hydrothermal growth system. Demonstrated samples included a family of high-quality and high-crystallinity anatase nanowire arrays with smooth, hierarchical or hyperbranched architectures, thanks to oriented attachment and crystallization as well as a self-assembly growth mechanism. The proposed hyperbranched arrays, consisting of long TiO2 nanowire trunks, short TiO2 nanorod branches as well as tiny TiO2 nanorod leaves (recall a tree with luxuriant foliage) and thus possessing a microscopic feature size, overcome typical shortages of insufficient dye adsorption for conventional 1D smooth nanowire arrays or prototype hierarchical nanowire arrays when applied to DSSC, which achieved for the first time similar dye uptakes (i.e. 90.10nmolcm−2vs 88.62nmolcm−2) as nanoparticle counterparts under the same thickness. Dye-sensitized solar cell fabricated with an ~8μm long novel hyperbranched nanowire arrays photoelectrode yields an impressive power conversion efficiency (PCE) of 8.11%, which was much greater than that of anatase TiO2 nanoparticle (20nm in diameter) counterpart due to synergistic effects of high dye uptakes and superior broadband light scattering for improved light harvesting as well as fast charge transport for efficient charge collection for the former.

Natural-dye-sensitised solar cells based on TiO2 nanotube arrays

Dye-sensitised solar cells (DSSCs) were fabricated using TiO2 nanotube array photoelectrodes with natural-dye sensitizers composed of extracts of mango, pumpkin and banana. Conversion of visible light into electricity was accomplished, with a performance comparable to any that has been reported for DSSCs based on TiO2 nanoparticles. The power conversion efficiencies of cells sensitised with dyes based on mango, pumpkin and banana extracts reached 0·15%, 0·06% and 0·21%, respectively, with short-circuit current densities of 0·44, 0·13 and 0·78 mA cm−2, respectively.

Improved photo-stability of silicon nanobelt arrays by atomic layer deposition for efficient photocatalytic hydrogen evolution

Silicon nanostructures have recently drawn great interest for use as photocathodes to produce hydrogen through water photoelectrolysis. Despite the high photocurrent observed, nanostructured Si photocathodes usually exhibit poor photo-stability in aqueous solution and rapidly deactivate. Herein, we report that by coating a thin titania protection layer using atomic layer deposition (ALD), the photo-stability of silicon nanobelt arrays fabricated by metal assisted chemical etching can be markedly improved. The photocurrent loss of the silicon nanobelt array photoelectrode coated with a 3 nm titania layer is found to be much lower than that of the electrode without a titania coating. We also demonstrate that the 3 nm titania coated Si nanobelt arrays can sustain more than twelve hours without a significant loss in photocurrent under operation conditions before it eventually fails. The possible failure mechanism is preliminarily investigated.

Enhanced photoelectrochemical property of gold nanoparticle sensitized TiO2 nanotube: A crucial investigation at electrode–electrolyte interface

We have reported for the first time a simple one step electrodeposition of gold nanoparticle (GNP) on TiO2 nanotube (TNT) structure and GNP sensitized TNT shows enhanced photoelectrochemical property than pristine TNT in visible region. GNP loaded TNT array photoelectrode has a broad visible light absorption (450–700nm) observed by UV–Vis spectroscopy. The GNPs are photoexcited due to plasmon resonance and facilitates the photogenerated electron–hole pair separation under visible illumination. Electrochemical impedance spectroscopy measurement ensures efficient electron transfer from nanoparticle to TNT. Charge transfer mechanism at electrode–electrolyte has also been investigated using Mott–Schottky analysis.

Controlled synthesis of Cu nanoparticles on TiO2 nanotube array photoelectrodes and their photoelectrochemical properties

TiO2 NTs/Cu photoelectrodes were prepared by coating Cu nanoparticles on the tube wall of the self-organized TiO2 nanotube arrays using a successive ionic layer adsorption and reaction method. The structural investigation by X-ray diffraction and scanning electron microscopy indicated that Cu nanoparticles grew uniformly on the walls of TiO2 nanotubes. The modification of Cu nanoparticles improved the photoresponse and photocurrent density of TiO2 NTs into the visible light region.

Stability of Photoactive Oxide Semiconductors

ZnxCd1-xSe quantum dot-sensitized TiO2 nanotube (TiO2 NT) array photoelectrodes were synthesized employing successive ionic layer adsorption and reaction (SILAR) technique. The influence of the number of deposition cycles and post-deposition annealing temperature on photoelectrochemical properties and stability behavior of photoanodes was investigated. The photoanodes were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Photoelectrochemical measurements indicated that TiO2 NTs coupled with ZnCdSe quantum dots synthesized with 7 SILAR cycles, annealed at 400oC for 1hr under N2 atmosphere exhibited excellent photoelectrochemical properties. The high and stable photocurrent produced demonstrates the potential of ZnxCd1-xSe/TiO2 heterostructure as an efficient photoanode.

The increased interface charge transfer in dye-sensitized solar cells based on well-ordered TiO2 nanotube arrays with different lengths

Abstract

Synthesis of ZnO nanoplates decorated rhombus-shaped ZnO nanorods and their application in solar cells

Novel nanostructures of ZnF(OH) nanoplates decorated rhombus-shaped ZnF(OH) nanorods were fabricated. The obtained precursors were transformed by calcination to porous hierarchical ZnO nanostructures with the original morphologies retained. Field emission scanning electron microscope images exhibit that the nanoplates are grown in the interstices between the nanorods and on the top of the nanorods. The structure and composition of the obtained products have been confirmed by transmission electron microscope and X-ray diffraction measurements. The obtained ZnO nanostructures have been successfully used in solar cells. The light-to-electricity conversion results show that the complex nanostructures exhibit a power conversion efficiency of 1.36% with a photoelectrode thickness of 4.2µm, which is comparable to those based on 40µm vertically aligned hexagonal-shaped ZnO nanowire array photoelectrodes. These results indicate that the synthesized ZnO nanoplate decorated rhombus-shaped ZnO nanorod nanostructures are more suitable for application as a photoelectrode in solar cells.

Photoelectrocatalytic degradation of 4-nonylphenol in water with WO3/TiO2 nanotube array photoelectrodes

WO3 decorated TiO2/Ti Nanotube arrays (WO3/TNAs) photoelectrodes were fabricated using in situ anodization and electrochemical deposition method. The morphology and structure of WO3/TNAs photoelectrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of different parameters, such as initial pH, bias potential and anions in solution, on photoelectrocatalytic (PEC) activity of WO3/TNAs photoelectrodes were investigated. The degradation mechanism and degradation products of 4-NP were analyzed using liquid-mass spectrometry (LC/MS). The results showed that the degradation percent of 4-nonylphenol (4-NP) on WO3/TNAs photoelectrodes could reach 90% under neutral conditions after 120min illumination. After a bias potential of 2.0V was applied, the degradation percent increased to 98% and the total organic carbon (TOC) removal efficiency was 60%. 4-NP transformed to carboxylic acid substances, CO2 and H2O by hydroxylation, dealkylation role, broken bonds and open-loop. Acid and base as well as SO42-, Cl−, HCO3- and NO3- ions in solution undermined the removal of 4-NP.

Reduced graphene oxide modified highly ordered TiO2 nanotube arrays photoelectrode with enhanced photoelectrocatalytic performance under visible-light irradiation.

In this paper, reduced graphene oxide modified highly ordered TiO2 nanotube arrays (RGO-TNTs) have been fabricated and used for photoelectrocatalytic (PEC) degradation of organic pollutants under visible light irradiation. Firstly, the RGO-TNT electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, FT-IR, X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. The responsive photocurrent and electrochemical impedance spectroscopy (EIS) results indicated that our present RGO-TNTs displayed superior photoresponsive and electron transfer performances compared with bare TNTs. Moreover, by comparison with bare TNT electrode, the RGO-TNT arrays showed stable and evidently improved PEC activity for degradation of methyl orange (MO) under visible light illumination. This might be attributed to the introduction of RGO, which extended the absorption edge and promoted electron-hole separation in the PEC process. Furthermore, owing to the synergetic effect of photocatalysis and electrocatalysis in the PEC process, the efficiency of PEC process (3.0 × 10(-3) min(-1)) is ca. 7.9 and 2.5 times faster than that of the electrochemical process (3.8 × 10(-4) min(-1)) and photocatalytic process (1.2 × 10(-3) min(-1)), respectively. Our investigation likely provides new opportunities for developing stable and efficient one-dimensional graphene modified TNT-based catalysts for PEC degradation of organic pollutants under visible light illumination.

Operation of lightly doped Si microwires under high-level injection conditions

The operation of lightly doped Si microwire arrays under high-level injection conditions was investigated by measurement of the current-potential behavior and carrier-collection efficiency of the wires in contact with non-aqueous electrolytes, and through complementary device physics simulations. The current-potential behavior of the lightly doped Si wire array photoelectrodes was dictated by both the radial contact and the carrier-selective back contact. For example, the Si microwire arrays exhibited n-type behavior when grown on a n+-doped substrate and placed in contact with the 1,1′-dimethylferrocene+/0–CH3OH redox system. The microwire arrays exhibited p-type behavior when grown on a p+-doped substrate and measured in contact with a redox system with a sufficiently negative Nernstian potential. The wire array photoelectrodes exhibited internal quantum yields of ∼0.8, deviating from unity for these radial devices. Device physics simulations of lightly doped n-Si wires in radial contact with the 1,1′-dimethylferrocene+/0–CH3OH redox system showed that the carrier-collection efficiency should be a strong function of the wire diameter and the carrier lifetime within the wire. Small diameter (d 400 nm) exhibited higher carrier collection efficiencies that were strongly dependent on the carrier lifetime in the wire, and wires with carrier lifetimes exceeding 5 μs were predicted to have near-unity quantum yields. The simulations and experimental measurements collectively indicated that the Si microwires possessed carrier lifetimes greater than 1 μs, and showed that radial structures with micron dimensions and high material quality can result in excellent device performance with lightly doped, structured semiconductors.

Application of ZnxCd1−xSe-sensitized TiO2 nanotube arrays as photoanodes for solar cells

This study reports the synthesis of ZnxCd1−xSe quantum dot-sensitized titania nanotube array photoelectrodes using a successive ionic layer adsorption and reaction technique and evaluates the photoelectrochemical performance as anodes. The effect of altering the number of sensitization cycles and annealing temperature on optical and photoelectrochemical properties of prepared photoanodes was studied. Surface morphology of the sensitized tubes was analyzed by scanning electron microscopy, while the phase composition was determined using X-ray diffraction and X-ray photoelectron spectroscopy techniques. Spectral response measurements indicated that TiO2 nanotube arrays coupled with ZnxCd1−xSe quantum dots synthesized in 7 cycles of deposition and annealed at 300 °C for 1 h under N2 exhibited excellent photoelectrochemical properties. The notably high photovoltaic characteristics demonstrate the potential of the ZnxCd1−xSe/TiO2 heterostructure as an efficient photoanode.

Effect of ZnS buffer layers in ZnO/ZnS/CdS nanorod array photoelectrode on the photoelectrochemical performance

ZnO/CdS/ZnS and ZnO/ZnS/CdS nanorod array photoelectrodes were constructed and fabricated by an alternative chemical bath deposition of CdS and ZnS layers onto the surface of the ZnO nanorod array. The photoelectrochemical performances of composite photoelectrodes were investigated, and the action mechanism of ZnS buffer layers was also considered. The results show that the ZnO/ZnS/CdS nanorod array photoelectrode possesses enhanced hydrogen production efficiency. The enhancement may be attributed to the ZnS buffer layers, which are advantageous in the separation and transportation of photogenerated electron–hole pairs in ZnO/ZnS/CdS nanorod array photoelectrodes.

Synthesis of Cu3BiS3 nanosheet films on TiO2 nanorod arrays by a solvothermal route and their photoelectrochemical characteristics

This paper presents an investigation on the synthesis and characterization of Cu3BiS3 nanosheet films on a TiO2/FTO substrate by a solvothermal route and the photoelectrochemical characteristics of the Cu3BiS3/TiO2 composite films are demonstrated as well. The results show that Cu3BiS3 nanosheets with an average thickness of 30 nm were successfully synthesized on the surface of TiO2 nanorod arrays. The photoelectric properties of the Cu3BiS3/TiO2 composite film indicate that the fill factor of the film photoelectrode is 60.8%, and the energy conversion efficiency is 1.281%, which is higher than that of a bare TiO2 nanorod array photoelectrode.