One-step Anodization Research Articles

A versatile electrochemical method to synthesize Co-CoO core-shell nanowires anodes for lithium ion batteries with superior stability and rate capability

A novel electrochemical method is proposed to synthesize nanostructured cobalt electrodes for lithium-ion batteries (LIBs). An array of cobalt nanowires (CoNWs) supported by a nanostructured copper current collector was obtained by the sequential electrodeposition of cobalt and copper into the nanopores of alumina templates and selective etching of alumina. The illustrated method can be implemented with one-side open alumina templates generated by one-step aluminium anodization, thus excluding the application alumina membranes and their coating by sputter metal deposition. The cobalt electrodeposition conditions allow to directly form Co-CoO core-shell nanowires, with metallic cobalt nanowires covered by a thin cobalt oxide film. The direct electrochemical growth of copper nanowires connected to CoNWs ensured high electronic conductivity and specific surface area of the resulting electrode, leading to a low interfacial impedance when used in lithium cell. This nanostructure and the enhanced lithium diffusion enabled by the nanowires morphology contributed to achieve a specific capacity of 1500 mAhg−1 after 200 cycles at 2 Ag-1, and complete restore of the capacity at 2 Ag-1 after cycling at the ultra-high current density of 450 Ag-1. The faradaic and capacitive contributions to charge storage were estimated by the analysis of cyclic voltammetry experiments carried out at different scan rates. Based on this latter analysis, pseudo-capacitive effects appear to play a pivotal role in determining the total recorded capacity. The advantages of the proposed method to sustain the large scale application of nanowires electrodes in lithium batteries are thoroughly discussed.

Cobalt-doped titanium oxide nanotubes grown via one-step anodization for water splitting applications

Titanium dioxide (TiO2) is one of the most utilized materials for water splitting applications; nonetheless, its poor exciton separation is a major hurdle towards its full realization as a catalyst for hydrogen (H2) production. This work presents a successful one-step method for the preparation of cobalt-doped TiO2 nanotubes. The wafers were prepared via the anodization of metallic titanium foils at two different potentials (20 and 60 V) in a cobalt-enriched electrolyte, in the presence of diethylenetriamine-pentaacetic acid (DTPA). Scanning Electron Microscopy (SEM) images of the prepared samples demonstrate the successful synthesis of homogeneous nanotube arrays. X-ray diffractometry and Raman spectroscopy confirm the insertion of cobalt as a dopant inside the anatase framework. Furthermore, the diffuse reflectance spectra of the samples are strongly affected by the presence of the dopant. As a consequence of the successful insertion, the current density developed by the doped samples under illumination is greatly enhanced, reaching up to a fourfold increase for the 60 V sample at a potential where the electrolysis of water takes place. The developed one-step method shows therefore great promise for future application in the production of photoelectroactive materials for H2 production.

Nanopatterning of crystalline silicon with anodized aluminum oxide templates

A novel thin film anodized aluminum oxide templating process was developed and applied to make nanopores with anisotropic etching on crystalline silicon through reactive ion etching, with the purpose of enhancing the anti-reflection of silicon substrates. A unique two-step anodizing method was introduced to create high quality nano-channels and it was demonstrated that this process is superior over a one-step anodization approach. It was found that pore to pore distance and pore density can be tuned by changing the applied potential within a range of 10–80 V. Optical characterization of the nanopatterned silicon showed an average 10% reduction in reflection in the UV–Vis wavelength range.

Porosity and hole diameter tuning on nanoporous anodic aluminium oxide membranes by one-step anodization

Nanoporous Aluminium (III) oxide was fabricated and characterized to determine its suitability as a microfiltration membrane and an antireflection coating. Aluminium (III) oxides were obtained using a one-step anodization process with Phosphoric acid (H3PO4) as electrolyte. The effect of the anodization voltage and electrolyte concentration were studied. Semi-ordered nanotubes were observed using a Scanning Electron Microscope. Porosity, pore diameter and interpore distance were obtained and were found to increase with an increase in anodization voltage. While the pore diameter and porosity increased with an increase in electrolyte concentration, the interpore distance was found to remain stable. The porosity was found to vary from 16% to 28% in the investigated range of parameters, while the pore diameter varied from 120 to 178 nm. Reflectance curves showed a wide range of low reflectance in the visible light region, which validates their applicability in the field of anti-reflection coatings.

Improvement the wastewater purification by TiO2 nanotube arrays: The effect of etching-step on the photo-generated charge carriers and photocatalytic activity of anodic TiO2 nanotubes

The current study demonstrates how the etching step in anodization process effects on the photocatalytic activity of TiO2 nanotubes. In this regard, the TiO2 nanotubes were made by one-step and two-step anodization process on two different substrates Ti and etched-Ti foils, respectively. The results revealed that two-step anodization process is a beneficial way to prepare highly well-organized structure and regular surface. The two-step anodization by an enhancement in the fluoride ions diffusion led to a decrease in nanotubes' porosity and an increment in the nanotubes’ surface area, a factor of roughness, and the ratio of length to diameter, respectively. As a consequence of the improvement in geometrical properties, the two-step TiO2 nanotubes led to the intensification of photocurrent density (from 0.383 to 0.677 mA cm−2) and photoconversion efficiency (from 0.18% to 0.29%) in comparison with the one-step nanotubes, respectively. Further, a synergetic impact of the photoelectrochemical measurement and photocatalytic process was observed. The degradation efficiencies of 2,4-dichlorophenol by two-step nanotubes increased from 47 to 55% under visible light, and from 58 to72% under UV irradiation, which it was attributed to more light harvesting, more photo-generated electrons, higher separation efficiency and improvement in geometrical properties. Furthermore, the kinetic study showed that the reactions follow first-order kinetics and the reaction rate constants by two-step nanotubes are 1.25 and 1.44 times as great as those of one-step nanotubes under visible and UV irradiation, respectively. Moreover, the reusability tests showed that 2-step TiO2 nanotubes has good stability and is active even up to the Fifth run.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au80Sn20 (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn2+ and AuCl4－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm−2 mM−1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.

High-Throughput Screening of Rat Mesenchymal Stem Cell Behavior on Gradient TiO2 Nanotubes.

The dimension of TiO2 nanotubes (TNTs) ranges from several nanometers to hundreds of nanometers. This variety raises the difficulty of screening suitable nanotube dimension for biomedical applications. Herein, we report the use of a simple one-step bipolar anodization method for fabrication of TNT gradients with diameter range from 30 to 100 nm. The gradient TNTs were successfully applied for high-throughput screening of TNT size effect on cell responses, including cell adhesion, proliferation, and differentiation. Results reveal that no significant difference in adherent cell number could be found within the range of 30-87 nm in both the presence and absence of serum proteins. On the contrary, large nanotubes (with outer diameter >87 nm) profoundly reduce cell adhesion in both the presence and absence of serum proteins, indicating TNT size could affect cell adhesion directly without the adsorbed proteins. The size effect on cell behavior becomes prominent with time that cell proliferation and differentiation decrease with increasing nanotube size. This size effect can be comprehended by protein adsorption and the formation of focal adhesion. Another two sample applications of gradient TNTs demonstrate gradient TNTs are promising for high-throughput screening.

Effect of synthesis parameters on visible light photocatalytic activity of graphene-TiO2 nanocomposites for industrial wastewater treatment

Reduced graphene oxide (RGO)-TiO2 nanotubes (TNTs) were used for industrial wastewater treatment that was obtained from Banwol Sihwa Industrial Complex, Korea. RGO-TNT were fabricated using one-step and two-step anodization at different RGO concentrations, RGO deposition times, anodization voltages and anodization times. Synthesized catalysts were characterised using FESEM, XRD, TEM, EDS, XPS, UV–vis DRS, PL, Raman, and pHPZC. Compared with pure-TNTs, two-step and one-step RGO-TNT exhibited 2.7 and 3.3-times higher photocatalytic activities for industrial wastewater. Scavenger experiments identified that OH and e− are main species involved in photocatalytic degradation of MB and industrial wastewater. RGO-TNTs are suitable for industrial wastewater treatment.

Enhanced field emission properties of the copper sulfide nanowalls with optimized 3-D morphology

The three-dimensional (3-D) copper sulfide nanowalls with sharp edges were successfully prepared by one-step anodization method. An interesting finding was that the morphology and microstructure of 3-D copper sulfide nanowalls can be regulated and optimized by abjusting the anodization time, and the corresponding field emission (FE) characteristics were significantly improved. The value of turn-on field can be dramatically reduced from 11.84 to 2.84 V/μm and the field enhancement factor up to 19899. Besides, the optimal 3-D copper sulfide nanowalls showed a long-term thermal stability and better conductivity. Preliminary researches indicate that as a promising field emitter, the 3-D copper sulfide nanowalls have potential applications in the field of vacuum micro- or nano-electronic devices.

One-step method for fabrication of superhydrophobic and superoleophilic surface for water-oil separation

A superhydrophobic and superoleophilic surface with micro-nano-binary scale structure and low surface energy coating was fabricated via one-step anodization process based on bare copper wire mesh. The water contact angle and water sliding angle of the prepared surface were 153° and 7.5° respectively, and the oil contact angle was 0°, the prepared surface showed excellent water repelling ability and superior absorption capacity for oil. Moreover, the prepared surface exhibits good resistance to saturation and corrosion. Furthermore, the prepared surface could separate many kinds of oil-water mixture efficiently. Even after 10 cycles, the separation efficiency still could reach above 87%. This study provided a low-cost and facial route to fabricate the surface which had high water-oil separation efficiency and excellent durability. Therefore this method had a promising application prospect.

Facile fabrication of superhydrophobic hybrid nanotip and nanopore arrays as surface-enhanced Raman spectroscopy substrates

We demonstrate the fabrication of superhydrophobic hybrid nanotip and nanopore arrays (NTNPAs) that can act as sensitive surface-enhanced Raman spectroscopy (SERS) substrates. The large-area substrates were fabricated by following a facile, low-cost process consisting of the one-step voltage-variation anodization of Al foil, followed by Ag nanoparticle deposition and fluorosilane (FS) modification. Uniformly distributed, large-area (5 × 5 cm2) NTNPAs can be obtained rapidly by anodizing Al foil for 1560 s followed by Ag deposition for 400 s, which showed good SERS reproducibility as using1 μM Rhodamine 6G (R6G) as analyte. SERS performances of superhydrophobic NTNPAs with different FS modification and Ag nanoparticle deposition orders were also studied. The nanosamples with FS modification followed by Ag nanoparticle deposition (FS-Ag) showed better SERS sensitivity than the nanosamples with Ag nanoparticle deposition followed by FS modification (Ag-FS). The detection limit of a directly dried R6G droplet can reach 10−8 M on the FS-Ag nanosamples. The results can help create practical high sensitive SERS substrates, which can be used in developing advanced bio- and chemical sensors.

Study of the highly ordered TiO2 nanotubes physical properties prepared with two-step anodization

Abstract Highly ordered hexagonal closely packed titanium dioxide nanotubes (TiO2 NTs) were successfully grown by a two-step anodization process. The TiO2 NTs were synthesized by electrochemical anodization of titanium foils in an ethylene glycol based electrolyte solution containing 0.3 wt% NH4F and 2 vol% deionized (DI) water at constant potential (50 V) for 1 h at room temperature. Physical properties of the TiO2 NTs, which were prepared via one and two-step anodization, were investigated. Atomic Force Microscopy (AFM) analysis revealed that anodization and subsequently peeled off the TiO2 NTs caused to the periodic pattern on the Ti surface. In order To study the nanotubes morphology, Field Emission Scanning Electron Microscopy (FESEM) was used, which was revealed that the two-step anodization resulted highly ordered hexagonal TiO2 NTs. Crystal structures of the TiO2 NTs were mainly anatase, determined by X-ray diffraction analysis. Optical studies were performed by Diffuse Reflection Spectra (DRS) and Photoluminescence (PL) analysis showed that the band gap of TiO2 NTs prepared via two-step anodization was lower than the band gap of samples prepared by one-step anodization process.

Preparation of Graphene/N-TiO<sub>2</sub> Nanoclusters by One Step Anodic Oxidation for Visible-Light-Driven Hydrogen Production

Titanium dioxide, as a promising photocatalytic material, has been widely used in the fields of environmental pollution control and photocatalytic water splitting to generate hydrogen. In this paper, graphene and N-doping TiO2composite film (GR/N-TiO2) electrode had been grown on titanium foil by one-step anodization, which was simple, time-saving and low cost. The electrode surface was lotusroot-like nanoclusters structure, which had a large specific surface area. The electrode exhibited an excellent optical absorption from ultraviolet to near infrared (200-2500 nm). This was due to the synergistic effects of graphene and N element, and the presence of oxygen vacancy defects. The results showed that the electrode had good electrochemical performances under simulated sunlight, its photocurrent density was about 0.7 mA/cm2, the light conversion efficiency was 0.35 %, and the hydrogen production rate was 34 μmol h-1cm-2. Thus, the prepared GR/N-TiO2film electrode had an excellent hydrogen production activity under sunlight and the potential of converting solar energy into hydrogen energy directly.

Electrochemical synthesis of self-organized TiO2 crystalline nanotubes without annealing

This work demonstrates that upon anodic polarization in an aqueous fluoride-containing electrolyte, TiO2 nanotube array films can be formed with a well-defined crystalline phase, rather than an amorphous one. The crystalline phase was obtained avoiding any high temperature annealing. We studied the formation of nanotubes in an HF/H2O medium and the development of crystalline grains on the nanotube wall, and we found a facile way to achieve crystalline TiO2 nanotube arrays through a one-step anodization. The crystallinity of the film was influenced by the synthesis parameters, and the optimization of the electrolyte composition and anodization conditions (applied voltage and time) were carried out. For comparison purposes, crystalline anatase TiO2 nanotubes were also prepared by thermal treatment of amorphous nanotubes grown in an organic bath (ethylene glycol/NH4F/H2O). The morphology and the crystallinity of the nanotubes were studied by field emission gun–scanning electron microscopy (FEG–SEM) and Raman spectroscopy, whereas the electrochemical and semiconducting properties were analyzed by means of linear sweep voltammetry, impedance spectroscopy, and Mott–Schottky plots. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) allowed us to determine the surface composition and the electronic structure of the samples and to correlate them with the electrochemical data. The optimal conditions to achieve a crystalline phase with high donor concentration are defined.

Tailoring of Morphology and Crystalline Structure of Nanoporous TiO2–TiO–TiN Composite Films for Enhanced Capacity as Anode Materials of Lithium-Ion Batteries

We report a novel three-dimensional nanoporous TiO2–TiO–TiN (Np-TTT) ternary composite film with cylindrical pores of diameter ϕ30–50 nm and laminated tier thickness of 10–30 nm, which was fabricated straightforwardly on a Ti foil via a one-step anodization in an aqueous nitric electrolyte. The Np-TTT composite films consisted of amorphous TiO2 matrix, quasi-crystalline TiO, and a small amount of TiN (∼2 at% as N), which are formed simultaneously during anodization through electrochemical and/or chemical reactions in the nitric electrolyte. As a binder-free and auxiliary-component-free anode material for lithium-ion batteries, the capacity and rate performance of the Np-TTT anodes were dependent on both the anodizing conditions and crystalline structure. Particularly, the Np-TTT composite film (∼800 nm-thick) that was annealed at 250°C for 1 h exhibited the highest areal specific capacity of 440 μAh cm−2 at the 1st cycle, a high retention of 95% from the 2nd to the 50th cycles, and a Coulombic efficiency of approximately 100%. The enhanced capacities of the Np-TTT composite films can be primarily attributed to the synergetic effect of the inclusion of conductive TiN component in bulk TiO2 matrix films, the active TiO with quasi-crystalline cubic phase, and nanoporous structure with high surface area.

Fabrication of Commercial Nanoporous Alumina by Low Voltage Anodizing

The present work is considered as an introductory study on the procurement of membranes from nanoporous alumina through one-step anodization. The nonporous alumina was obtained by anodizing the specimens at low voltage 5V for 20 minutes in phosphoric acid. The self-ordered porous arrangements can be acquired by using this process. The variables of space between pores, high pore density on the alumina surface are subjected to comparison with membranes which obtained by other methods. The mixture of phosphoric acid and chromium trioxide is used for removing the formed aluminum oxide after the first anodization. The self-ordered porous configuration is obtained at the second anodization step at the same conditions of the first anodization process. The nonporous alumina membrane was subjected to characterization of its surface morphology by scanning electron microscopy SEM and the electric properties were examined by using the electrochemical impedance test EIS. The formed nanoporous structures can be used for fabrication of sensor elements.

Ordered nanopore arrays with large interpore distances via one-step anodization.

Preparation of pre-patterned alumina substrates using bottom-up techniques compatible with nanotechnology applications is still a challenge. We present a novel methodology to achieve superior order in 'anodic' alumina with large interpore distances by a convenient one-step anodization process. The use of transparent insulators renders such anodic layers applicable as templates for nanostructured photovoltaic or photoelectrochemical devices.

The Photocatalytic Properties and Mechanistic Study of ZnO,Ag Multiphase Co-Composited TiO2 Nanotube Arrays Film Prepared by One-Step Anodization Method

ZnO/Ag multi-phase composited TiO2 nanotube arrays (TiO2 TNAs) films were prepared on pure Ti substrate through one-step anodizing method using double pulse plating power supply. The deposition amount of Ag and ZnO were adjusted by changing the concentration of Zn(NO3)2·6H2O and AgNO3 and reverse voltage. The results showed that ZnO deposited in the wall of TiO2 NTAs dispersedly; sedimentary phase and dispersed phase are the two forms of deposited Ag in TiO2 NTAs. The bandgap narrowed 0.33 eV, and the recombination rate of photo-generated electron-hole pairs also decreased obviously due to the doping energy level synergistic effect of ZnO and the Surface Plasmon Resonance (SPR) effect of Ag. Furthermore, the sample with 1 mM ZnO+0.4 mM Ag and 5 V reverse voltage has the best photocatalytic properties, the degradation rate of Methylene blue (MB) reached 86% which improved 15% compared with undoped TiO2 NTAs.

A high-performance supercapacitor electrode based on three-dimensional poly-rowed copper hydroxide nanorods on copper foam

Three-dimensional (3D) poly-rowed copper hydroxide [Cu(OH)2] nanorods nanostructures have been synthesized on copper foam slices, using copper foam as copper source, current collector and 3D substrate, through a facile and scalable one-step anodization method. The synthesized products can be directly used as binder free electrodes of supercapacitors. The synthesized material exhibited a 3D connect and quasi connect network structure which can facilitate ion mobility and increase the amount of active sites for redox reactions. These merits together lead to a high areal specific capacitance of 1.889 F cm−2 at a scan rate of 2 mV s−1, excellent rate capability (75.39% retention upon increasing the current density by 15 times), low intrinsic resistance (0.792 Ω cm−2) and good cycling stability (87.23% capacitance retention after 5000 cycles), demonstrating a good potential for high performance energy storage devices applications.

Electrodeposition of cobalt nanowires into alumina templates generated by one-step anodization

The electrodeposition of cobalt nanowires into nanoporous alumina templates produced by one-step anodization of low-purity aluminium was investigated. Aluminium was electropolished prior anodization to generate a hexagonal cell pattern, and a tree-like structure was introduced at the aluminium/aluminium oxide interface by progressively decreasing the anodization potential following potentiostatic anodization. Pulsed electrodeposition including the periodic application of a cathodic potential pulse with constant amplitude was performed to fill the generated alumina template by cobalt nanowires. With this strategy, cathodic potential pulses with amplitude lower than −5 V (vs. Ag/AgCl) were necessary to enforce uniform and instantaneous cobalt nucleation at the bottom of template nanopores, which allowed achieving uniform filling and narrow length distribution of the electrodeposited nanowires. However, the uniform growth of the nucleating cobalt nanowires could be sustained by considerably less cathodic potential pulses (up to −1.5 V vs. Ag/AgCl). Uniform filling of the alumina template could accordingly be achieved by a two-stage-pulsed electrodeposition strategy including the application of a high cathodic pulse (<−5 V) inducing uniform and instantaneous cobalt nucleation followed by the periodic application of a lower cathodic pulse (>−1.5 V) sustaining nanowire growth. The mechanisms that govern cobalt nucleation at the bottom of nanopores and the technical advantages of the proposed nanowire synthesis strategy are discussed.