TiO2 Nanotube Arrays Electrode Research Articles

Enhanced capacitive performance of TiO2 nanotubes with molybdenum oxide coating

Alpha-phase MoO3 is electrochemically deposited on well-aligned TiO2 nanotubes which are synthesized by anodic oxidation. The morphology, composition and electrochemical behaviors of MoO3-coated and bare TiO2 nanotubes are studied. The former deliver greatly higher capacitance than the latter and their performance can be readily optimized by varying MoO3 deposition cycles. The large areal capacitance of 209.6mFcm−2 at a scan rate of 5mVs−1 is firstly achieved for TiO2 nanotube array electrode. In addition, the coated TiO2 nanotubes show significantly more capacitance than a dense MoO3 film. For example, they exhibit a capacitance up to 74.9Fg−1 at 5mVs−1 in 1M KCl solution, while the dense film only shows a capacitance of 32.3Fg−1 under same conditions. Such improvement is found ascribed to MoO3 with high pseudocapacity and TiO2 nanotubes with large surface area allowing efficient MoO3 nanoparticle loading and rapid charge transfer. This nanostructured electrode with features of facile synthesis and excellent performance is believed as a potential candidate for supercapacitor applications.

High-performance and renewable supercapacitors based on TiO2 nanotube array electrodes treated by an electrochemical doping approach

Although one-dimensional anodic TiO2 nanotube arrays have shown promise as supercapacitor electrode materials, their poor electronic conductivity embarrasses the practical applications. Here, we develop a simple electrochemical doping method to significantly improve the electronic conductivity and the electrochemical performances of TiO2 nanotube electrodes. These TiO2 nanotube electrodes treated by the electrochemical hydrogenation doping (TiO2-H) exhibit a very high average specific capacitance of 20.08 mF cm−2 at a current density of 0.05mAcm−2, ∼20 times more than the pristine TiO2 nanotube electrodes. The improved electrochemical performances can be attributed to ultrahigh conductivity of TiO2-H due to the introduction of interstitial hydrogen ions and oxygen vacancies by the doping. The supercapacitor device assembled by the doped electrodes delivers a specific capacitance of 5.42 mF cm−2 and power density of 27.66 mW cm−2, on average, at the current density of 0.05mAcm−2. The device also shows an outstanding rate capability with 60% specific capacitance retained when the current density increases from 0.05 to 4.00mAcm−2. More interestingly, the electrochemical performances of the supercapacitor after cycling can be recovered by the same doping process. This strategy boosts the performances of the supercapacitor, especially cycling stability.

A novel self-cleaning, non-enzymatic glucose sensor working under a very low applied potential based on a Pt nanoparticle-decorated TiO2 nanotube array electrode

In this paper, a non-enzymatic amperometric glucose sensor working under a very low applied potential of −0.5V (vs. saturated calomel electrode or SCE) was developed based on a Pt nanoparticle-decorated TiO2 nanotube array (Pt/TiO2 NTA) electrode. A highly ordered TiO2 NTA with a diameter of 200nm was fabricated by anodization of Ti in ethylene glycol containing 0.5wt% NH4F, 10vol% H2O, and 0.9vol% H2SO4. Pt nanoparticles ∼5nm in diameter were uniformly decorated inside the TiO2 nanotubes through ion-exchange reaction with Pt (NH3)4Cl2, followed by reduction with NaBH4. The morphology of the electrode was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The performance of the as-prepared electrode was characterized by cyclic voltammetry and chronoamperometry. The sensor can accurately detect glucose in 0.1M NaOH solution at an applied potential of −0.5V (vs. SCE) in the presence of interferences, such as ascorbic acid and uric acid, with a linear range of 1–15mM and a detection limit of 0.2mM at a signal-to-noise ratio of 3. The Pt/TiO2 synergistic effect shows a good self-cleaning ability. The electrocatalytic ability of the present Pt/TiO2 NTA electrode toward glucose oxidation under a very low applied potential has promising applications in blood glucose measurement and mediator-free anodes for glucose biofuel cells.

Silver sulfide nanoparticles sensitized titanium dioxide nanotube arrays synthesized by in situ sulfurization for photocatalytic hydrogen production

Titanium dioxide (TiO2) nanotube arrays (TNAs) sensitized with silver sulfide (Ag2S) nanoparticles (NPs) were synthesized via facile in situ sulfurization. Metallic silver NPs were first loaded on TNAs through a simple electrodeposition process. The as-prepared Ag/TNAs composites were further treated with a solution of acetonitrile containing sulfur (S8) and dried in vacuum to obtain a new nanocomposite material comprising of TNAs sensitized with Ag2S NPs. In these composite nanostructures, ultrafine Ag2S NPs were well-dispersed and assembled on the exterior and interior walls of the TNAs. Owing to sensitizing with a narrow bandgap material like Ag2S and the homogeneous distribution of the Ag2S NP heterojunction structures over the surface of the TNAs, the synthesized nanocomposite samples exhibited remarkable capability to absorb visible light and showed a significant enhancement in the photocatalytic efficiency of hydrogen generation. Under visible light illumination (100mW/cm2), a maximum photoconversion efficiency of 1.21% and the highest hydrogen production rate of 1.13mL/cm2h were obtained from the TNA electrodes sensitized with Ag2S NPs.

Synthesis of visible-light absorbing CoFe2O4 sensitized TiO2 nanotube arrays electrode with enhanced photoelectrochemical performance

TiO2 nanotube arrays sensitized with CoFe2O4 nanocrystals were successfully synthesized via a facile hydrothermal method. The as-prepared sample was studied by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX) to characterize its phase structure, morphology and chemical composition. Enhanced absorption in both UV and visible-light regions was observed for the CoFe2O4 sensitized TiO2 nanotube arrays. The photocurrent density of CoFe2O4 sensitized TiO2 nanotube arrays electrode was 30 times as great as that of bare TiO2 nanotube arrays electrode.

Photoelectrocatalytic determination of chemical oxygen demand under visible light using Cu2O-loaded TiO2 nanotube arrays electrode

A novel, visible light responsive chemical oxygen demand (COD) determination method using a Cu2O-loaded TiO2 nanotube arrays (TNTAs) electrode as sensor was proposed. In comparison with the pure TNTAs, the composite electrode showed much enhancement in the photocurrent response in visible region. With a positive bias potential of 0.3V (vs. Ag/AgCl) and visible light illumination, a COD detection limit of 15mgL−1 COD and a linear range of 20–300mgL−1 COD were achieved by the present composite electrode. When the composite electrode was used for the test of real wastewater samples, the obtained values were in good agreement with those determined by the standard K2Cr2O7 COD determination method. This paper would provide a potential outdoor COD determination method utilizing solar energy.

Factors Influencing Hydroxyl Radical Formation in a Photo-Induced Confined Etching System

In this paper, we studied the formation of free OH on a TiO2nanotube array electrode in a photo-induced confined etching system. We used fluorescence spectroscopy, transient photocurrent response, electrochemical impedance spectroscopy(EIS), and Mott- Schottky analysis to investigate the influence of several key factors, including the applied potential, the illumination time, and the pH value. The highest efficiency for the photoelectrocatalytic formation of free OH on the TiO2nanotube array electrode was achieved at an applied potential of 1.0 V(vs a saturated calomel electrode(SCE)); the photoelectrocatalytic generation and consumption of free OH quickly approached a steady state in this system, as the confined etching layer formed by OH remained stable during illumination. This may allow good control of the etching precision during continuous etching processes. The highest efficiency for the photoelectrocatalytic formation of free OH on the TiO2nanotube array electrode was observed at pH 10. The results have an important significance for regulating and optimizing photo-induced confined etching system, which can be used to improve the etching speed or the leveling precision during the planarization of copper.

Photoelectrocatalytic Performance of Benzoic Acid onTiO2Nanotube Array Electrodes

The photoelectrocatalytic performance of benzoic acid on TiO2nanotube array electrodes was investigated. A thin-cell was used to discuss the effect of the bias voltage, illumination intensity, and electrolyte concentration on the photoelectrocatalytic degradation efficiency of benzoic acid. The photogenerated current-time (I-t) profiles were found to be related to the adsorption and the degradation process. The relationship between the initial concentration and the photocurrent peaks (I0ph) fits the Langmuir-type adsorption model, thus confirming that the adsorption of benzoic acid on TiO2nanotube arrays (TNAs) was single monolayer adsorption. At low concentrations, theI-tprofiles simply decay after the initial transient peak due to the sufficient holes on the TNAs which would oxidize the benzoic acid quickly. However, theI-tprofiles varied with increasing benzoic acid concentrations because the rate of diffusion in the bulk solution and the degradation of the intermediate products affect the photoelectrocatalysis on the electrode surface.

Free standing TiO2 nanotube array electrodes with an ultra-thin Al2O3 barrier layer and TiCl4 surface modification for highly efficient dye sensitized solar cells

Dye sensitized solar cells were fabricated with free standing TiO2 nanotube (TNT) array films, which were prepared by template assisted atomic layer deposition (ALD) with precise wall thickness control. Efforts to improve the photovoltaic performance were made by using Al2O3 barrier layer coating in conjunction with TiCl4 surface modification. An Al2O3 thin layer was deposited on the TNT electrode by ALD to serve as the charge recombination barrier, but it suffers from the drawback of decreasing the photoelectron injection from dye into TiO2 when the barrier layer became too thick. With the TiCl4 treatment in combination with optimal thickness coating, this problem could be avoided. The co-surface treated electrode presents superior surface property with low recombination rate and good electron transport property. A high conversion efficiency of 8.62% is obtained, which is about 1.8 times that of the device without surface modifications.

Electrochemical fabrication of lanthanum-doped TiO2 nanotube array electrode and investigation of its photoelectrochemical capability

Highly ordered lanthanum-doped (La-doped) TiO2 nanotube arrays were prepared by electrochemical anodization process on a Ti sheet, followed by cathodic electrochemical process using lanthanum nitrate solution as the La source, and at last were analyzed by SEM, XPS, FTIR, XRD, and DRS characterization techniques. The analytical results demonstrated that the La doping could promoted phase transformation of TiO2 from the anatase to rutile. Red shifted and enhanced absorption intensities of certain peaks in both UV and visible light regions were also observed. Moreover, a new state of Ti3+ was founded after calcinations. The photoelectrochemical results indicated that La doping can significantly enhance the photoconversion efficiency of the TiO2 nanotube array electrode. The maximum photoconversion efficiency was 0.598%, which was obviously more than 2-fold higher than the undoped one (0.257%) under the same supporting electrolyte solution. The photoelectrocatalytic (PEC) degradation result of p-nitrophenol (PNP) was used to investigate the PEC activities of the as-prepared electrode. The La-doped TiO2 nanotube array electrode showed much higher degradation efficiencies (99.33%) than the undoped TiO2 nanotube array electrode (70.16%) under the same condition.

Gold nanoparticle–polypyrrole composite modified TiO2 nanotube array electrode for the amperometric sensing of ascorbic acid

Titanium dioxide (TiO2) nanotubes were fabricated by anodisation of titanium foil in 0.15 M ammonium fluoride in an aqueous solution of glycerol (90 % v/v). Electropolymerisation of pyrrole and deposition of gold nanoparticles on to the TiO2 nanotube array electrode were carried out by cyclic voltammetry (CV). Electrochemical characterization of the sensor was performed by CV and electrochemical impedance spectroscopy. The morphology of the electrode was studied after every step of modification using field emission scanning electron microscope and atomic force microscope. The sensor was tested for AA and other biomolecules in phosphate buffered saline solution of pH 7 using CV, differential pulse voltammetry and amperometry. The sensor exhibited very high sensitivity of 63.912 μA mM−1 cm−2 and excellent selectivity to ascorbic acid (AA) in the presence of other biomolecules such as uric acid, dopamine, glucose and para-acetaminophen. It also showed very good linearity (R = 0.9995) over a wide range (1 μM–5 mM) of detection. The sensor was tested for AA in lemon and found its concentration to be 339 mg ml−1.

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.

High-Efficiency Degradation Sugar Wastewater by Co-TiO2 Nanotube Arrays

This work presents a novel approach for preparing TiO2 nanotube arrays loaded with highly dispersed Co nanoparticles through an ultrasound aided photochemical route. The Co content doped on the arrays was controlled by changing the concentration of Co(NO3)2 and the ultrasound time. The Co doped TiO2 nanotube arrays were characterized by SEM, XRD, EDS and UV–Vis spectrum. The photocatalytic activities of TiO2 nanotube arrays electrode were studied. The results showed that Co doping significantly enhanced the photocatalytic degradation rate of TiO2 nanotube arrays under UV-light irradiation. The main factors affected photocatalytic degradation of sugar wastewater such as the illumination time, pH, different concentrations of H2O2 and wastewater with undoped TiO2 nanotube arrays were compared. The results showed that the longer the exposure time, the higher the initial pH of wastewater is more favorable for the Co-TiO2 nanotube arrays, The concentration of H2O2 is 60mmol/L, and compared to undoped TiO2 nanotube arrays Co doped TiO2 nanotube arrays have better photocatalytic properties.

Enhanced Electrochromic Properties by Using a CeO<SUB>2</SUB> Modified TiO<SUB>2</SUB> Nanotube Array Transparent Counter Electrode

A new kind of electrochromic device composed of a CeO2 modified TiO2 nanotube array counter electrode and a working electrode of P3MeT film was reported. The counter electrode was fabricated by electrodepositing CeO2 nanoparticles onto the walls of anodized TiO2 nanotubes. The CeO2 modified TiO2 nanotube array counter electrode keeps a high transparency under working voltage. The charge capacity of CeO2 modified TiO2 nanotube array has an increase of 30% than that of un-modified TiO2 nanotube array electrode. Compared with the electrochromic device with a TiO2 nanotube array film electrode, the CeO2 modified TiO2 nanotube counter electrode based EC device has a fast decoloration time of 0.8 s. The fast response attributes to the high effective surface area and the fast charge transportation along the nanotube walls.

Enhanced Visible‐Light‐Induced Photoelectrocatalytic Degradation of Methyl Orange by CdS Sensitized TiO2 Nanotube Arrays Electrode

AbstractIn this work, CdS sensitized TiO2 nanotube arrays (CdS/TiO2NTs) electrode was synthesized with the CdS deposition on the highly ordered titanium dioxide nanotube arrays (TiO2NTs) by sequential chemical bath deposition method (S‐CBD). The as‐prepared CdS/TiO2NTs was characterized by field‐emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD). The results indicated that the CdS nanoparticles were effectively deposited on the surface of TiO2NTs. The amperometric I‐t curve on the CdS/TiO2NTs electrode was also presented. It was found that the photocurrent density was enhanced significantly from 0.5 to 1.85 mA/cm2 upon illumination with applied potential of 0.5 V at the central wavelength of 253.7 nm. The photoelectrocatalytic (PEC) activity of the CdS/TiO2NTs electrode was investigated by degradation of methyl orange (MO) in aqueous solution. Compared with TiO2NTs electrode, the degradation efficiencies of CdS/TiO2NTs electrode increased from 78% to 99.2% under UV light in 2 h, and from 14% to 99.2% under visible light in 3 h, which was caused by effective separation of the electrons and holes due to the effect of CdS, hence inhibiting the recombination of electron/hole pairs of TiO2NTs.

Synthesis and characterization of polythiophene-modified TiO2 nanotube arrays

The highly ordered and uniform TiO2 nanotube arrays were fabricated by anodic oxidation method and PTh(polythiophene)/TiO2 nanotube arrays electrode were obtained by electrochemical polymerization. X-ray powder diffraction (XRD) analysis confirmed the formation of TiO2 phase. The morphologies and optical characteristics of the TiO2 nanotube arrays were studied by scanning electron microscope (SEM), UV-Vis absorption spectra and Raman spectra. The results demonstrate that the PTh/TiO2 electrode could enlarge the visible light absorption region and increase the photocurrent in visible region. The modified TiO2 electrode with light-to-electric energy conversion efficiency of 1·46%, the short-circuit current density of 4·52 mAcm − 2, open-circuit voltage of 0·74 V and fill factor of 0·44, were obtained.

Preparation and electrocatalytic activity of gold nanoparticle embedded in highly ordered TiO2 nanotube array electrode for electro-oxidation of galactose

Gold nanoparticle–TiO2 nanotube electrodes with high surface area have been successfully prepared using a two step process consisting of galvanic deposition of gold nanoparticles on TiO2 nanotubes/Ti electrodes as support. TiO2 nanotubes/Ti electrodes are fabricated by anodising titanium foil in a dimethyl sulphoxide fluoride containing electrolyte. Scanning electron microscopy and energy dispersive X-ray spectroscopy results indicate that the TiO2 nanotube layers consist of individual tubes of about 60–90 nm diameters, and gold nanoparticles with a size range of 30–40 nm are well dispersed on the surface of the TiO2 nanotube support. The electrocatalytic properties of gold nanoparticle–TiO2 nanotube electrodes towards the electro-oxidation of galactose are investigated by cyclic voltammetry. Compared with pure gold electrodes, gold nanoparticles–TiO2 nanotube electrodes show much higher electrochemical activity. This novel electrode can be used repeatedly and exhibits stable electrocatalytic activity for galactose oxidation.

Cyclic voltammetry studies of TiO2 nanotube arrays electrode: Conductivity and reactivity in the presence of H+ and aqueous redox systems

In this paper, we use cyclic voltammetry to investigate the effect of protons on the conductivity and reactivity of TiO2 nanotube array (NTA) electrodes in an aqueous redox system. The H+ ion can change the TiO2 nanotube (anatase phase) surface states for electrons transfer. It can also act as an intermediate state for electron transfer to the acceptor species in the electrolyte surrounding the TiO2. The higher the concentration of H+ ions in the aqueous electrolyte, the easier it is for the electrons transfer from the TiO2 to the electrolyte oxidized species. The reduction is facile, with a similar reduction potential for various acceptor species, but re-oxidation is not possible. It is apparently an electrochemical reduction involving a single-proton transfer and single-electron transfer. Based on this conclusion, an electrode (PB/Au/TiO2 NTAs) was fabricated by means of electrodeposition. The electrode used to detect hydrogen peroxide. The sensitivity of the detector is high, and its the detection limit can be as low as 100nM.

Synthesis and Photoinduced Charge-Transfer Properties of a ZnFe2O4-Sensitized TiO2 Nanotube Array Electrode

TiO2 nanotube arrays sensitized with ZnFe2O4 nano-crystals were successfully fabricated by a two-step process of anodization and a vacuum-assistant impregnation method followed by annealing. The sample was studied by an environmental scanning electron microscope, a transmission electron microscope, energy-dispersive X-ray analysis, and X-ray diffraction to characterize its morphology and chemical composition. Ultraviolet-visible (UV-vis) absorption spectra and a photoelectrochemical measurement approved that the ZnFe2O4 sensitization enhanced the probability of photoinduced charge separation and extended the range of the photoresponse of TiO2 nanotube arrays from the UV to visible region. In addition, the behaviors of photoinduced charge transfer in a TiO2 nanotube array electrode before and after sensitization by ZnFe2O4 nanocrystals were comparatively studied. The photoluminescence of the TiO2 nanotube array electrode became suppressed, and the surface photovoltage responses on the spectrum were significantly enhanced after the introduction of ZnFe2O4 nanocrystals. The transfer dynamics of the photoinduced charges were observed directly by a transient photovoltage measurement, which revealed a fast charge separation at the interface between ZnFe2O4 nanocrystals and TiO2 nanotubes upon light excitation.

Enhanced photoelectrochemical properties of Cu2O-loaded short TiO2 nanotube array electrode prepared by sonoelectrochemical deposition

Enhanced photoelectrochemical properties of Cu2O-loaded short TiO2 nanotube array electrode prepared by sonoelectrochemical deposition