Anodization Conditions Research Articles

Electrochemical functionalization at anodic conditions of multi-walled carbon nanotubes with chlorodiphenylphosphine

Covalent functionalization of multi-walled carbon nanotubes (MWCNTs) and oxidized MWCNTs (o-MWCNTs) with chlorodiphenylphosphine (Ph2PCl) has been studied by cyclic voltammetry in organic medium. Depending the upper potential limit used in the electrochemical functionalization, different amount of phosphorus incorporation n is obtained, as result of the formation of radical species during the electrochemical oxidation of the Ph2PCl. The electrochemical oxidation of Ph2PCl promotes the covalent attachment of diphenylphosphine-like structure on the carbon nanotube surface. At the same time, the incorporation of Cl on the carbon nanotubes is observed during the functionalization. Furthermore, the presence of oxygen surface groups on the MWCNTs provides a favorable attachment of the Ph2P∙+ species, which has promoted preferentially the formation of CP bonds, whereas the amount of Cl is reduced.

Tuning the visible light activity of tungsten oxide layers by changing the anodization conditions

Photoelectrochemical water splitting under solar radiation is one of the most studied methods of solar-to-fuel energy conversion. The search for effective photoelectrode materials operating under solar radiation is still ongoing, and in this paper, it is shown how to control the optical and photoelectrochemical properties of anodic tungsten oxide layers by changing the anodizing potential. Anodic tungsten oxide layers were obtained in an aqueous electrolyte with 1 M ammonium sulfate and 75 mM ammonium fluoride at a constant voltage of 20–70 V and annealed at 500 °C in air. Comprehensive characterization of materials was performed using SEM, XRD, UV–Vis DRS, Mott-Schottky analyses, and photoelectrochemical water splitting tests. It was found that with increasing the anodizing potential the band gap narrows from 3.09 eV to 2.75 eV, donor density increases, and the IPCE spectrum shifts towards the visible light range.

Electrocarboxylation of N-Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids.

Direct electrocarboxylation of various N-acylimines with atmospheric CO2 is achieved in an undivided cell under mild conditions, affording substituted α-amino acids in yields of 62-95%. This reaction is conducted with high efficiency using triethanolamine as an external reductant under nonsacrificial anode conditions, and can be facilely performed on gram scale. Preliminary mechanistic studies including cyclic voltammetry and control experiments support N-radical carbanion as the key intermediate.

Single Particle Electrochemical Oxidation of Polyvinylpyrrolidone-Capped Silver Nanospheres, Nanocubes, and Nanoplates in Potassium Nitrate and Potassium Hydroxide Solutions

Single particle electrochemical oxidation of polyvinylpyrrolidone-capped silver nanoparticles at a microdisk electrode is investigated as a function of particle shape (spheres, cubes, and plates) in potassium nitrate and potassium hydroxide solutions. In potassium nitrate, extreme anodic potentials (≥1500 mV vs Ag/AgCl (3 M KCl)) are necessary to achieve oxidation, while lower anodic potentials are required in potassium hydroxide (≥900 mV vs Ag/AgCl (saturated KCl)). Upon oxidation, silver oxide is formed, readily catalyzing water oxidation, producing a spike-step current response. The spike duration for each particle is used to probe effects of particle shape on the oxidation mechanism, and is substantially shorter in nitrate solution at the large overpotentials than in hydroxide solution. The integration of current spikes indicates oxidation to a mixed-valence complex. In both electrolytes, the rate of silver oxidation strongly depends on silver content of the nanoparticles, rather than the shape-dependent variable–surface area. The step height, which reflects rate of water oxidation, also tracks the silver content more so than shape. The reactivity of less-protected citrate-capped particles toward silver oxidation is also compared with that of the polymer-capped particles under these anodic conditions in the nitrate and hydroxide solutions.

Anodic Shock-Triggered Exsolution of Metal Nanoparticles from Perovskite Oxide

Nanoparticles decorated electrodes (NDEs) are useful in fuel cells, electrolyzers, water treatment, and chemical synthesis. Here, we show that by rapidly bringing a mixed ionic-electronic conductor outside its electrochemical stability window, one can achieve uniform dispersion of metallic nanoparticles inside its bulk and at the surface and improve its electrocatalytic performance when back under normal functional conditions. Surprisingly, this can happen under anodic as well as cathodic current/voltage shocks in an ABO3 perovskite oxide, La0.4Ca0.4Ti0.88Fe0.06Ni0.06O3-δ (LCTFN), across a wide range of H2/O2 gas environments at 800 °C. One possible mechanism for bulk Fe0/Ni0 precipitation under anodic shock condition is the incomplete oxygen oxidation (O2- → Oα-, 0 < α < 2), migration and escape of oxygen to interfaces, and "whiplash" transition-metal reduction due to low electronic conductivity. We show that both cathodic and anodic shocks can produce NDEs to enhance electrocatalytic performance, potentially improving the flexibility of this approach in practical devices.

High temperature oxidation of AISI 441 in simulated solid oxide fuel cell anode side conditions

This study investigates the corrosion of AISI 441 in simulated anode conditions of solid oxide fuel cells (SOFCs). Several parameters such as temperature, humidity, surface condition, pre-oxidation temperature and environment, were investigated. Samples pre-oxidized at 800 ºC were protective at 550–900 ºC, while as-received samples showed protective behavior only at 900 ºC. Additional exposures performed at 600 ºC revealed the negative effect of increasing steam concentration, the beneficial effect of grinding, while pre-oxidation at 600 ºC did not improve the protectiveness. The role and the interplay of the aforementioned factors are discussed.

A study on the minute change of the alumina surface structure according to the anodizing conditions for the production of a robust wettability-modified surfaces

The anodizing method of aluminum has been loved by the industry by forming a mechanically and chemically robust Al2O3 layer on the surface of aluminum, and various researches have been reported to expand the applicability. In particular, superhydrophilic/superhydrophobic surface modification through anodization can take advantage of change in wettability and at the same time secure surface robustness, thus it can be said to be a very promising technology in the industry. In this study, changes in the surface structure of the Al2O3 layer according to the anodizing conditions were observed, and changes in mechanical robustness and wettability were closely analyzed. Through the minute change of anodization condition, conventional nanoporous structures and novel nanofibrous structures were fabricated. The nanofibers could form in two different shapes depending on the current density. To characterize their surface properties, mechanical and wetting properties were measured. The nanoporous structures were found to have excellent mechanical properties. The nanofibrous structures were found to be advantageous as they maximized the wetting properties, resulting in either a slippery or sticky superhydrophobic surface. The investigation of structural diversification and surface properties offers a guideline to choosing the optimal anodization condition depending on the application.

Anodal Transcranial Direct Current Stimulation Does Not Affect Velocity Loss During a Typical Resistance Exercise Session

ABSTRACT Purpose: This study investigated the effects of transcranial direct current stimulation (tDCS) on velocity loss in a typical resistance exercise session. Methods: Twelve recreationally resistance-trained males (age = 24.8 ± 3.0 years, body mass = 78.9 ± 13.6 kg, and height = 174.3 ± 7.3 cm) completed two experimental trials in a counterbalanced crossover design: anodal tDCS and sham conditions. The stimuli were applied over the left dorsolateral prefrontal cortex for 20 minutes, using a 2 mA current intensity in anodal tDCS and a 1-minute active stimulus in the sham condition. After stimulation, subjects performed three sets of the bench press at a 70% of 1 maximum repetition intensity and 1 min of inter-set rest. The velocity loss was calculated as the relative difference between the fastest repetition velocity (usually first) and the velocity of the last repetition of each set and averaged over all three sets. Results: The results found no interaction between conditions and sets (P = .122), and no effect for conditions (P = .323) or sets (P = .364) for the velocity loss in each set. Also, no differences were found between the average velocity loss of the three sets in the anodal tDCS (-25.0 ± 4.7%) and sham condition (-23.3 ± 6.4%; P = .323). Conclusion: Anodal tDCS does not affect movement velocity in a typical strength training protocol in recreationally trained subjects.

Designing Carbon-Enriched Alumina Films Possessing Visible Light Absorption.

Aluminum anodization in an aqueous solution of formic acid and sodium vanadate leads to the formation of alumina/carbon composite films. This process was optimized by varying the concentrations of formic acid and sodium vanadate, the pH, and the processing time in constant-voltage (60–100 V) or constant-current mode. As estimated, in this electrolyte, the anodizing conditions played a critical role in forming thick, nanoporous anodic films with surprisingly high carbon content up to 17 at.%. The morphology and composition of these films were examined by scanning electron microscopy, ellipsometry, EDS mapping, and thermogravimetry coupled with mass spectrometry. For the analysis of incorporated carbon species, X-ray photoelectron and Auger spectroscopies were applied, indicating the presence of carbon in both the sp2 and the sp3 states. For these films, the Tauc plots derived from the experimental diffuse reflectance spectra revealed an unprecedentedly low bandgap (Eg) of 1.78 eV compared with the characteristic Eg values of alumina films formed in solutions of other carboxylic acids under conventional anodization conditions and visible-light absorption.

Fast Charging Anode Materials for Lithium‐Ion Batteries: Current Status and Perspectives

AbstractWith the enormous development of the electric vehicle market, fast charging battery technology is highly required. However, the slow kinetics and lithium plating under fast charging condition of traditional graphite anode hinder the fast charging capability of lithium‐ion batteries. To develop anode materials with rapid Li‐ions diffusion capability and fast reaction kinetics has received widely attentions. This review summarizes the current status in the exploration of fast charging anode materials, mainly including the critical challenge of achieving fast charging capability, the inherent structures and lithium storage mechanisms of various anode materials, as well as the recent progress to improve the rate performance involving morphology regulation, structure design, surface/interface modification, as well as forming multiphase systems. Finally, the challenges and future directions of developing fast charging Li‐ion batteries are highlighted.

Laccase immobilization on nanoporous aluminum oxide for black liquor treatment

Nanoporous aluminum oxide coating has been successfully synthesized using different anodic synthesis conditions and self-assembled nanoporous with variable pore diameter, thickness and porosity were obtained. The Anodic Aluminum Oxide (AAO) coatings exhibited appropriate morphological characteristics which were employed for the Phebia brevispora BAFC 633 Laccase immobilization. Principal component analysis demonstrated that pH, contact time and enzyme concentration were the main variables which explain the total variation among the Laccase immobilization in the samples. The highest enzymatic activity was reported in the sample synthesized to 0.3 M of electrolyte concentration, 40°C of temperature and 30 V of anodization voltage. Laccase specific activity of 4.1 Ucm−2 could be obtained using an enzymatic concentration of 3.209 UL−1, pH 4.39 and contact time of 1.18 h according to the proposed regression model. Laccase/AAO bionanocatalyst can be easily collected and reserved 95.6% of initial activity after four cycles tests and immobilization yield of around 18.1%. Application of the immobilized Laccase for Black Liquor removal was also investigated. The bionanocatalyst showed better pH stability, 40% higher BL removal efficiency compared to free laccase after 40 min of reaction, and the ability to be collected and used up to twice for BL treatment. The novelty of this work contemplates the development of a bionanocatalyst from a nanoporous coating and immobilized Laccases that can be successfully applied for the treatment of effluents contaminated with black liquor.

Effect of Dense Oxide Film Thickness on the Growth of Lower Layer Nanotubes

There are two opposite mechanisms for the growth of anodic TiO2 nanotubes. One is the field-assisted dissolution and ejection theory, the other is the oxygen bubble mold. In order to prove the latter mechanism is right, we constructed a three-layer nanotube structure (upper layer nanotubes + dense oxide film + lower layer nanotubes), which was obtained by three steps anodization. The upper and lower layers nanotubes are separated by a dense oxide film. When the dense oxide film is thin, the lower layer nanotubes is longer than the upper layer nanotubes. On the contrary, when the dense oxide film is thick, the lower layer nanotubes is shorter than the upper layer nanotubes. In either case, the anodization conditions of the upper and lower layer nanotubes are the same. This could not be explained by field-assisted dissolution theory. By analyzing the curve, we introduce a new method to decide the time of entering the third stage of the anodization, which is the main stage of nanotubes growth. With the second anodization voltage increases, the time edge entering the third stage become longer, which means the time to growth the nanotubes becomes shorter, and finally leading the different length of the nanotubes.

High-definition transcranial direct current stimulation of the dorsal anterior cingulate cortex modulates decision-making and executive control.

Previous neuroimaging evidence highlights the translational implications of targeting the dorsal anterior cingulate cortex (dACC), i.e. a key node of the networks underlying conflict monitoring and decision-making, in brain stimulation treatments with clinical or rehabilitative purposes. While the optimized modelling of "high-definition" current flows between multiple anode-cathode pairs might, in principle, allow to stimulate an otherwise challenging target, sensitive benchmark metrics of dACC neuromodulation are required to assess the effectiveness of this approach. On this basis, we aimed to assess the modulatory effect of anodal and cathodal high-definition tDCS (HD-tDCS) of the dACC on different facets of executive control and decision-making in healthy young individuals. A combined modelling/targeting procedure provided the optimal montage for the maximum intensity of dACC stimulation with six small "high-definition" electrodes delivering anodal, cathodal or sham HD-tDCS for 20min in a within-subject design with three separate sessions. Following stimulation, participants performed Flanker and gambling tasks unveiling individual differences in executive control and both loss- and risk-aversion in decision-making, respectively. Compared to both anodal and sham conditions, cathodal dACC stimulation significantly affected task performance by increasing control over the Flanker conflict effect, and both loss and risk-aversion in decision-making. By confirming the feasibility and effectiveness of dACC stimulation with HD-tDCS, these findings highlight the implications of modelling and targeting procedures for neuromodulation in clinical research, whereby innovative protocols might serve as treatment addressing dysfunctional dACC activity, or combined with cognitive training, to enhance higher-order executive functioning in different neuropsychiatric conditions.

NIR-Reflective and Hydrophobic Bio-Inspired Nano-Holed Configurations on Titanium Alloy.

Near-infrared (NIR) radiation plays an important role in guided external stimulus therapies; its application in bone-related treatments is becoming more and more frequent. Therefore, metallic biomaterials that exhibit properties activated by NIR are promising for further orthopedic procedures. In this work, we present an adapted electroforming approach to attain a biomorphic nano-holed TiO2 coating on Ti6Al4V alloy. Through a precise control of the anodization conditions, structures revealed the formation of localized nano-pores arranged in a periodic assembly. This specific organization provoked higher stability against thermal oxidation and precise hydrophobic wettability behavior according to Cassie-Baxter's model; both characteristics are a prerequisite to ensure a favorable biological response in an implantable structure for guided bone regeneration. In addition, the periodically arranged sub-wavelength-sized unit cell on the metallic-dielectric structure exhibits a peculiar optical response, which results in higher NIR reflectivity. Accordingly, we have proved that this effect enhances the efficiency of the scattering processes and provokes a significant improvement of light confinement producing a spontaneous NIR fluorescence emission. The combination of the already favorable mechanical and biocompatibility properties of Ti6Al4V, along with suitable thermal stability, wetting, and electro-optical behavior, opens a promising path toward strategic bone therapeutic procedures.

Electrochemical characteristic assessments toward 2,4,6-trinitrotoluene using anodic TiO2 nanotube arrays

The feasibility of electrochemical detection of 2,4,6-trinitrotoluene (2,4,6-TNT) using TiO2 nanotubes synthesized through electrochemical anodization of Ti was explored. TiO2 nanotube arrays with distinctly different surface features, including an initiation layer and tube wall structures, were prepared, and the efficacy for the electrochemical reduction of 2,4,6-TNT was comparatively evaluated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrochemical sensing properties of the anodic TiO2 nanotubes were not affected by the surface morphology based on the different anodization conditions. The mechanism governing the mass transfer of 2,4,6-TNT during electrochemical reduction was dominated by diffusion, as determined based on LSV analyses at various scan rates. Importantly, the TiO2 nanotube arrays can distinguish 2,4,6-TNT and cyclotrimethylenetrinitramine (RDX) in mixture solutions of 2,4,6-TNT, RDX, and pentaerythritol tetranitrate (PETN), with four distinct reduction peaks in the voltammogram. Further studies are needed to enhance the efficacy of the TiO2 nanotube arrays for the electrochemical reduction of explosive compounds, where introducing metal dopants, quantum dots, or vacancy engineering are prospectively effective strategies.

Effect of polarization potentials on tribocorrosion behavior of Monel 400 alloy in seawater environment

Monel 400 alloy is widely used in marine engineering due to its corrosion resistance. In this study, the tribocorrosion behavior of Monel 400 alloy has been investigated under cathodic and anodic polarization conditions. The results revealed that the material loss increased under both cathodic and anodic polarization, while the damage mechanism varied. Under cathodic polarization condition, the damage is caused by delamination of the worn surface and crack propagation in the subsurface, which gets more seriously at more negative polarization values. Under higher anodic polarization values, the lubricating performance of in-situ generated corrosion product was weakened. As the anodic polarization value increased, the diameter of corrosion products increased and got easier to be sheared-off during the sliding process.

Formation process of zirconia nanotubes and porous structures and model of oxygen bubble growth

Preparation and growth mechanism of anodization of Ti and Al has been widely concerned for two decades, but the research on anodic ZrO2 is relatively lacking. In this paper, anodic TiO2 and ZrO2 nanotubes were prepared in glycerol electrolyte containing 0.35 M NH4F and 4 vol% H2O under different anodizing voltages. We had successfully prepared the anodic ZrO2 nanotubes (AZNTs) with a complete top and a “bulb” at the bottom under 60 V, and with the increase of the applied anodizing voltage, the “bulb” cavity also increased. However, under the same anodizing conditions, the surface of anodic TiO2 nanotubes (ATNTs) is a cluster of nano-tip morphology, and the bottom of the ATNTs is a conventional hemisphere shape. In addition, both AZNTs and porous anodic zirconia (PAZ) were found to coexist in the anodic ZrO2 layer prepared at 60 V. Here, we used the oxygen bubble model and ionic current and electronic current theories to analyze the reason of the special morphology. It is confirmed that the porous anodic oxides are actually evolved from nanotubes. In other words, the structure is essentially the same.

Towards stable and highly active IrO2 catalysts supported on doped tin oxides for the oxygen evolution reaction in acidic media

Iridium oxide is the preferred catalyst for water oxidation but it is required to maximize its utilization to deploy Proton Exchange Membrane Water Electrolyzers (PEMWEs) into the large-scale applications panorama. A promising pathway for dispersing this precious catalyst is on an electric conductive and stable support. However, there is a lack of understanding how the support-catalyst interactions affect the stability/activity of the electrocatalyst under anodic conditions. This work discloses a modified, easy-scalable, polyol synthesis protocol to produce a highly active and stable iridium-based catalyst, supported on metal-doped tin oxides. The loading of Ir was reduced 30 wt.% compared to the reference IrO2, and dispersed on Sb-SnO2 (IrOx/ATO), In-SnO2 (IrOx/ITO) and SnO2 supports. All synthesized electrocatalysts not only surpassed the OER-mass activity of a commercial catalyst (IrO2) – reference – but also reached higher electrochemical active surface areas and enhanced stability under the OER conditions. The highest performance was achieved with Ir NPs supported on ITO (176 A/gIr vs. 15.5 A/gIr for the reference catalyst @ 1.51 V vs. RHE) and both IrOx/ITO and IrOx/SnO2 catalysts demonstrated remarkable stability after cycling the electrode and performing long-term chronopotentiometry. ITO is, therefore, an auspicious support to serve Ir-based catalysts as it favors a good bargain between activity and stability, while drastically reducing the amount of noble metal.

Morphological and Structural Study of Anodized Titanium Grade 2, Using HCl in Aqueous Solution

In this work, the electrochemical anodization process was carried out on titanium grade 2, using an electrolytic solution of 3 M and 0.15 M HCl with voltages of 11 V, 12 V and 15 V, as well as time variations in the experimental process and later an annealing process at 750 °C. According to the results obtained, the TiO2 coatings presented different morphologies on their surface, which consisted of nanopores, nanowires and clusters of oxide grains, as well as a combination of anatase and rutile crystalline phases. Band Gap variations were found to be non-significant despite changes in the morphology of the coatings at different anodization conditions, with an average value of 2.91 eV. It was observed that the anodized samples treated by the annealing process at 750 °C, thickness values up to 16 μm were obtained.

Performance of Reduced Titanium Oxide and Boron Doped Diamond as anodes in hyperthermophilic bioelectrochemical systems

This work investigates Reduced Titanium Oxide (RTO) in comparison with Carbon Cloth (CC) and commercial Boron Doped Diamond (BDD) as anodes in hyperthermophilic bioelectrochemical systems operating at 80°C by Thermotoga neapolitana. Two samples of RTO were synthesized by plasma electrolytic oxidation (PEO) of titanium plates and subsequent electrochemical reduction. Electrochemical performance of CC, BDD, and RTO are tested by performing cyclic voltammetry in the anodic region (0-1V, 50 mV/s), in abiotic and biotic conditions. The surface of colonized materials is observed by SEM microscopy. Results show that bacteria fast settle on all tested material, significantly affecting their electrochemical conductivity. The integration of voltammetric cycles reveals that biofilm generates capacitive effects on the anodic surfaces, particularly evident in RTO, less in CC and absent in BDD. Charge densities provided by capacitive response of RTO and CC are of the order of 5.58 and 0.77 mC/cm2, respectively.