Nanotube Array Photoelectrodes Research Articles

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.

Preparation of Highly Ordered TiO<SUB>2</SUB> Nanotube Array Photoelectrode for the Photoelectrocatalytic Degradation of Methyl Blue: Activity and Mechanism Study

Preparation of Highly Ordered TiO<SUB>2</SUB> Nanotube Array Photoelectrode for the Photoelectrocatalytic Degradation of Methyl Blue: Activity and Mechanism Study

Preparation of graphene film decorated TiO2 nano-tube array photoelectrode and its enhanced visible light photocatalytic mechanism

Graphene film decorated TiO2 nano-tube array (GF/TiO2 NTA) photoelectrodes were prepared through anodization, followed by electrodeposition strategy. Morphologies and structures of the resulting GF/TiO2 NTA samples were characterized by scanning electrons microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. In addition, the optical and photoelectrochemical properties were investigated through UV–visible light diffuse reflection spectroscopy, photocurrent response and Mott–Schottky analysis. Furthermore, the photodecomposition performances were investigated through yield of hydroxyl radicals and photocatalytic (PC) degradation of methyl blue (MB) under visible light irradiation. It was found that GF/TiO2 NTA photoelectrode exhibited intense light absorption both in UV light and visible region, higher transient photoinduced current of 0.107mAcm−2 and charge carrier concentration of 0.84×1019cm−3, as well as effective PC performance of 65.9% for the degradation of MB. Furthermore, contribution of several reactive species to the PC efficiency of GF/TiO2 NTA photoelectrode was distinguished. Moreover, the enhanced visible light PC mechanism was proposed and confirmed in detail.

Research on the effect of crystal structures on W-TiO2 nanotube array photoelectrodes by theoretical and experimental methods

W-doped/undoped TiO2 nanotube array (TNAs) photoelectrodes with different nanostructures were successfully fabricated using the anodization method. Their morphology and characteristics were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and ultra violet/visible light diffuse reflectance spectra (UV/vis/DRS). Their electronic structure and optical properties were studied by means of first-principle. Photocatalytic (PC) performance of W-TNAs photoelectrodes with different crystal structures was evaluated using the decomposition rates of Rhodamine B (Rh.B) under xenon light illumination. The results demonstrated that W substituting Ti broadened the width of conduction band (CB) and valence band (VB) of anatase and rutile TiO2, reduced the band gap of rutile TiO2 and even caused its red-shift. W incorporated into TNAs photoelectrodes extended light absorption threshold and enhanced its utilization of solar light and PC activity, particularly, the PC performance of W-TNAs photoelectrodes with mixed crystal and rutile crystal structure.

Effect of Post-Annealing Treatment on Photocatalytic and Photoelectrocatalytic Performances of TiO<SUB>2</SUB> Nanotube Arrays Photoelectrode

Highly ordered TiO2 nano-tube arrays (TNTAs) photoelectrodes were prepared through anodization method, followed by annealing treatment. Morphologies and structures of the as-prepared TNTAs samples were investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, the optical and photoelectrochemical (PECH) properties were investigated through ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and transient photocurrent response. Furthermore, the photodecomposition performances were investigated through the yield of hydroxyl (*OH) radicals and photocatalytic (PC) degradation of RhB under Xenon light irradiation. Results indicated that the TNTAs samples annealed at 723 K exhibited the highest photocurrent response, PC performance and yield of *OH radicals, in which 60.8% of RhB could be degraded by PC degradation within 60 min. The high PC performance could mainly be attributed to the anatase structure, high crystallinity and highly ordered nano-tubular structure, which favored the transfer and separation of photoinduced charge carriers. This study suggests that highly ordered nano-structure could provide superior pathway for the charge transfer and separation.

N-doped TiO2 nanotube array photoelectrode for visible-light-induced photoelectrochemical and photoelectrocatalytic activities

N-doped TiO2 nanotube arrays (TiO2NTs) were prepared by hydrothermal treatment of the crystalline TiO2NTs, and characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (DRS). The highly ordered TiO2NTs with an inner diameter of approximately 80nm and a tube length of about 400nm were obtained. XRD patterns showed that the TiO2 nanotube arrays before and after N doping were anatase. XPS analysis indicated that N was doped into the TiO2 lattice. A shift of the absorption edge to a low energy was observed from DRS. N-doped TiO2NTs electrode exhibited higher photoelectrochemical and photoelectrocatalytic activities than the undoped TiO2NTs electrode. The electrochemical impedance spectroscopy and photoluminescence spectra confirmed that doping N promoted the separation of the photogenerated electrons and holes.

Construction of N, S codoped TiO2 NCs decorated TiO2 nano-tube array photoelectrode and its enhanced visible light photocatalytic mechanism

In the present work, N, S codoped TiO2 nano-crystallites (NCs) decorated TiO2 nano-tube arrays (N-S-TiO2 NCs/TNTAs) photoelectrodes have been successfully constructed through anodization method, followed by evaporation induced self-assembly (EISA) strategy. The structures of N-S-TiO2 NCs/TNTAs samples were characterized by scanning electrons microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron microscopy (XPS). Results indicated that TNTAs was partly covered by N, S codoped TiO2 NCs. Meanwhile, N elements coexisted in the forms of substitutional N (Ti–N and N–Ti–O) and interstitial N (Ti–O–N) in TiO2, while S elements were also incorporated into the lattice of TiO2 through substituting titanium atom and coexisted in the cationic forms of S6+ and S4+. In addition, optical and photoelectrochemical (PECH) properties of the as-prepared N-S-TiO2 NCs/TNTAs samples were investigated through UV–vis light diffuse reflection spectroscopy (DRS), transient open circuit potential (OCP), photocurrent response (PCR) and electro-chemical impedance spectroscopy (EIS). Furthermore, photodecomposition performances were evaluated by the yield of OH radicals and photocatalytic (PC) degradation of methyl blue (MB) under Xenon lamp irradiation. All results showed that N-S-TiO2 NCs/TNTAs photoelectrode exhibited intense visible light absorption ranging from 400 to 700nm, high transient photoinduced current of 0.115mAcm−2, open circuit photovoltage of −0.312mVcm−2, generation of hydroxyl radicals and PC efficiency of 59.7% for the degradation of MB. The enhanced PC performance could mainly be attributed to the decoration of N, S codoped TiO2 NCs, which could not only enhance the light absorption in visible region but also improve the transfer and separation efficiency of photoinduced charge carriers.

CdS quantum dots-sensitized TiO2 nanotube arrays for solar cells

CdS quantum dots(QDs) sensitized TiO2 nanotube arrays photoelectrodes were investigated for their photovoltaic performance of quantum dots-sensitized solar cells. The highly ordered TiO2 nanotube arrays(TNAs) were synthesized on Ti foils by anodic oxidation method. Then CdS quantum dots were deposited onto the TiO2 nanotube arrays by successive ionic layer absorption and reaction(SILAR) method to serve as the sensitizers. Cd(NO3)2 and Na2S were used as the precursor materials of Cd+ and S2− ions, respectively. It is found that the CdS QDs sensitizer may significantly increase the light response of TiO2 nanotube arrays. With increasing CdS QDs deposition cycles, the visible light response increases. Maximum photocurrent was obtained for the QDs that have an absorption peak at about 500 nm. Under AM 1.5 G illuminations(100 mW cm−2), a 4.85 mA/cm2 short circuit current density was achieved, and the maximium energy conversion efficiency of the asprepared CdS QDs-sensitized TNAs solar cells was obtained as high as 0.81 % at five SILAR cycles.

Photoelectrochemical performance of CdTe sensitized TiO2 nanotube array photoelectrodes

CdTe and ZnS quantum dots sensitized TiO2 nanotube array photoelectrodes were prepared by depositing CdTe and ZnS QDs on the tube walls of the self-organized TiO2 NTs using successive ionic layer adsorption and reaction (SILAR) technique. The deposition of CdTe and ZnS 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 obtained results indicated that TiO2 NTs photoelectrodes sensitized by CdTe quantum dots for 5 cycles exhibited excellent photoelectrochemical properties, with an open-circuit voltage of 0.95V and a short circuit current density of 11.15mAcm−2, and ZnS coating protected the photoelectrodes against photocorrosion.

A photoelectrochemical immunosensor for tris(2,3-dibromopropyl) isocyanurate detection with a multiple hybrid CdTe/Au–TiO2 nanotube arrays

In this paper, tris(2,3-dibromopropyl) isocyanurate (TBC) is for the first time as far as we know determined by ultrasensitive photoelectrochemical (PEC) immunoassay using an antibody-modified ternary hybrid CdTe/Au-TiO2 nanotube arrays (NTAs) photoelectrode, developed by the pulse electrodeposition technique. The as-prepared hybrid shows enhanced photon absorption and photocurrent response, which subsequently increased the photoelectrical conversion efficiency in the visible region. TBC-antibody (Ab) was developed in rabbits as a result of immunization with the BSA-TBC conjugate and covalently cross-linked onto the CdTe/Au-TiO2 NTAs. Since the photocurrent is highly dependent on the TiO2 surface properties, the specific interaction between TBC and the antibody results in a sensitive change in the photocurrent, which displayed a linear range of 5.0 × 10(-11) to 5.0 × 10(-5) M and a low detection limit of 5.0 × 10(-11) M for TBC determination. This proposed strategy highlights the application of TiO2 nanotube in visible-light-activated photoelectrochemical biosensing, which could largely reduce the destructive effect of UV light on biomolecules.

A novel method for the preparation of a photocorrosion stable core/shell CdTe/CdS quantum dot TiO2 nanotube array photoelectrode demonstrating an AM 1.5G photoconversion efficiency of 6.12%

Type-II core/shell CdTe/CdS quantum dots (QDs) are assembled onto TiO2 nanotube array (NTA) films using a bi-functional linker molecule with the help of a hydrothermal method coupled with successive ionic layer adsorption and reaction process. Spatial separation of the electron and hole wave functions within the core/shell heterostructured nanocrystals appears to result in an extended charge separation state, resulting in a significant increase in photocurrent and excellent device stability. When only CdS or CdTe QDs are used as the sensitizer, the largest photocurrent densities are 1.31 mA cm−2 and 1.23 mA cm−2, respectively. For the core/shell CdTe/CdS QDs sensitized TiO2 NTA photoelectrodes the photocurrent density increases to ≈9.17 mA cm−2, dramatically larger than the values obtained with only one sensitizer. The core/shell CdTe/CdS QDs sensitized TiO2 NTA photoelectrodes provide a remarkable photoelectrochemical cell efficiency of 6.12%. To the best of our knowledge this photoconversion efficiency is the highest in the field of QD-sensitized photoelectrodes. A corresponding hydrogen evolution rate as high as 1560 μmol h−1 W−1 was achieved.

Influence of post-treatment temperature of TNTa photoelectrodes on photoelectrochemical properties and photocatalytic degradation of 4-nonylphenol

TiO2/Ti Nanotube array (TNTa) photoelectrodes were prepared by galvanostatic and potentiostatic anodization technique, and annealed at different temperature. The morphology and structure were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectra. Optical properties and photoelectrochemical (PECH) properties were investigated by surface photovoltage (SPV), ultra UV–vis diffuse reflectance spectra (UV/vis/DRS), open-circuit potential (OCP) and transient photocurrent. Photodecomposition performances were evaluated by the yield of •OH radicals and photocatalytic (PC) degradation rate of 4-nonylphenol (4-NP) under xenon light. The results showed that with the increase of post-treatment temperature, PECH and PC properties increased gradually and then decreased. The photocurrent densities, yield of ⁎OH radicals and photodecomposition rates of 4-NP were following the trend of TNT-823>TNT-873>TNT-773>TNT-673>TNT-973>TNT-298. When the annealing temperature was 823K, the photoelectrodes were composed of mixed crystal structure and ordered nanotube array, which exhibited superior PECH properties. When the annealed temperature arrived to 973K, the nanotube collapsed and the PECH and PC properties of TNTa photoelectrodes decreased. For TNT-823 photoelectrodes, after the assistant potential was applied, the degradation rate of 4-NP increased significantly from 77% to 97% after 120min illumination.

CdSe/CdS quantum dots co-sensitized TiO2 nanotube array photoelectrode for highly efficient solar cells

In this work, we designed and fabricated a novel one-dimensional CdSe/CdS@TiO2 core–shell nanotube array for quantum dots co-sensitized solar cells (QDSSCs) application. The three-component core–shell nanotube array structure was formed cascade by coating CdS nanoparticles with a successive ionic layer adsorption and reaction process and a thin CdSe layer by chemical bath deposition onto the vertical TiO2 nanotube arrays (TNAs), which enhanced the optical absorption in the visible region and presented an stepwise band-edge level structure to improve the charge separation. Under optimum conditions, the CdS/CdSe co-sensitized QDSSC demonstrated a power conversion efficiency (PCE) of 2.40% under 100mW/cm2 illumination of simulate sunlight. Furthermore, an improved QDSSC with a PCE up to 2.74% was obtained by sealed annealing of TNAs, due to the transformation of thin and smooth nanotube to thick and rough particle nanotube.

Dynamics Study on the Cerium and Oxidative Cerium Modified TiO2Nanotube Arrays for Hydrogen Production by Water Splitting Using Electrochemical Impedance Spectrum

TiO2 nanotube arrays photoelectrodes were prepared by anode oxidation on pure Ti sheet. The donor material glycol (C2H6O2) added in the anode electrolyte significantly reduced the charge transfer im- pedance of TiO2 nanotubes to promote the photocatalytic water splitting for hydrogen production. TiO2 nanotube arrays electrodes were modified by cerium and oxidative cerium with electrochemical deposition and anodic oxidation. The flat band potential moves to the negative potential direction after modification. Electrochemical impedance spectrum (EIS) measurement was used to investigate the electron transfer char- acteristic in photoelectrodes and the interface characteristic in the photoelectrochemical cell (PEC) for hydrogen production. Arcs of EIS and corresponding electrode processes were discussed. Dynamic parameters of the electrodes were calculated by reasonable electrical equivalent circuit fitting. The results indicate that TiO2 nanotube arrays electrode modified by cerium and oxidative cerium could largely decrease the electron transfer resistance which contributes to hydrogen production. The mechanism of the cerium and oxidative cerium acting on TiO2 nanotube arrays to promote charge transfer is discussed.

Self-ordering anodized nanotubes: Enhancing the performance by surface plasmon for dye-sensitized solar cell

In the present work, electrochemical anodization has been used to prepare uniform TiO2 nanotube array photoelectrode. The average internal diameter, tube length and wall thickness of the optimized morphology is ∼180nm, 14μm and 10nm, respectively. It was found that the tube diameter increases with the anodization voltage. Diffraction data reveals that the nanotubes consist solely of anatase phase. Back illuminated geometry of dye-sensitized solar cell (DSSC), with nanotubes grown at 60V for 2h, gave a cell performance of 4.5%. TiO2 nanotubes are loaded with silver (Ag) nanoparticles synthesized by a hydrothermal route. The Ag particle size is controlled resulting in solar conversion efficiency to increase by 22%. The DSSC based on TiO2 nanotube with Ag nanoparticles shows power conversion efficiency of 5.5%. Detailed characterization are performed, presented and discussed.

A photoelectrochemical study of CdS modified TiO2 nanotube arrays as photoanodes for cathodic protection of stainless steel

An electrodeposited CdS nanoparticles-modified highly-ordered TiO2 nanotube arrays (CdS–TNs) photoelectrode and its performance of photocathodic protection are reported. The self-organized TiO2 nanotube arrays are fabricated by electrochemical anodization in an organic–inorganic mixed electrolyte and sensitized with CdS nanoparticles by electrodeposition via a single-step direct current. The morphology, crystalline phase, and composition of the CdS–TNs films were characterized systematically by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet–visible (UV–Vis) spectroscopy, respectively. The photoelectrochemical performances of the CdS–TNs film under illumination and dark conditions in 0.5M NaCl solution were evaluated through the electrochemical measurements. It is indicated that the TNs incorporated by CdS effectively harvest solar light in the UV as well as the visible light (up to 480nm) region. It is supposed that the high photoelectro-response activity of the CdS–TNs is attributed to the increased efficiency of charge separation and transport of electrons. The electrode potentials of 304 stainless steel coupled with the CdS–TNs is found to be negatively shifted for about 246mV and 215mV under UV and white light irradiation, respectively, which can be remained for 24h even in darkness. It is implied that the CdS–TNs are able to effectively function a photogenerated cathodic protection for metals both under the UV and visible light illumination.

Fabrication and characterization of CdS-sensitized TiO2 nanotube photoelectrode

CdS quantum dot (Qd)-sensitized TiO2 nanotube array photoelectrode is synthesised via a two-step method on tin-doped In2O3-coated (ITO) glass substrate. TiO2 nanotube arrays are prepared in the ethylene glycol electrolyte solution by anodizing titanium films which are deposited on ITO glass substrate by radio frequency sputtering. Then, the CdS Qds are deposited on the nanotubes by successive ionic layer adsorption and reaction technique. The resulting nanotube arrays are characterized by scanning electron microscopy, X-ray diffraction (XRD) and UV–visible absorption spectroscopy. The length of the obtained nanotubes reaches 1.60 μm and their inner diameter and wall thickness are around 90 and 20 nm, respectively. The XRD results show that the as-prepared TiO2 nanotubes array is amorphous, which are converted to anatase TiO2 after annealed at 450 °C for 2 h. The CdS Qds deposited on the TiO2 nanotubes shift the absorption edge of TiO2 from 388 to 494 nm. The results show that the CdS-sensitized TiO2 nanotubes array film can be used as the photoelectrode for solar cells.

Photoelectric performance of TiO2 nanotube array photoelectrodes cosensitized with CdS/CdSe quantum dots

The photoresponse of TiO2 nanotube-array films in the visible region is shown to have been significantly improved by sensitizing them with CdS and CdSe semiconductor quantum dots using a sequential chemical bath deposition method. These quantum dots served as cosensitizers, and the performance of corresponding photoelectrode was measured in a photoelectrochemical solar cell. A 13.0 mA/cm2 short circuit current density is achieved with the TiO2/CdS/CdSe photoelectrode under AM 1.5G illuminations, which is higher than the direct sum of CdS and CdSe sensitized TiO2.

A new glass substrate photoelectrocatalytic electrode for efficient visible-light hydrogen production: CdS sensitized TiO2 nanotube arrays

Transparent and visible-light-response CdS sensitized TiO2 nanotube arrays (TNAs) photoelectrode was fabricated on conductive glass with the aim to improve the mechanical stability and light utilization of traditional Ti-foil-based titania nanotubes electrode. The sample was studied by FESEM, EDX and XPS to characterize its morphology and chemical compostion. UV–vis absorption spectra and photoelectrochemical measurement approved that the CdS coating enhanced the visible spectrum absorption of the TiO2 nanotube array, as well as their solar-spectrum induced photocurrents. Under visible-light AM 1.5 illumination (100mW/cm2) the composite photoelectrode generate hydrogen from water containing sulfide ions at a rate of 1.12mL/cm2h, nearly 7.46 times higher than that of pure TNAs or 11.79 times than that of commercial P25 glass electrode. Such kind of material will has potential application in solar water splitting and other fields.

Fabrication of uniform Ag/TiO2 nanotube array structures with enhanced photoelectrochemical performance

In the current work, pulse current deposition has been used to prepare evenly distributed and uniformly sized Ag nanoparticles on a TiO2 nanotube array photoelectrode. The Ag particle size and loading were controlled by the pulse deposition time. The Ag/TiO2 nanotube arrays were characterized by SEM, TEM, XRD, XPS and UV-vis diffuse reflection absorption. The resulting electrode contained intimately coupled, three-dimensional Ag/TiO2 structures with greatly improved photocurrent generation and charge transfer compared to a two-dimensional random Ag particle layer deposited directly on top of the nanotube array by the regular photoinduction method. A model mechanism is proposed to illustrate the uniform Ag nanoparticle deposition via the new deposition technique developed in the current work that promotes the uniform distribution of the Ag particles whilst minimizing their deposition at tube entrances, thus effectively preventing the pores from becoming clogged.