Anodization Conditions Research Articles

Experimental Investigation of Long-term Ageing Effect on the Structural and Electrochemical Behaviour of Self-organized TiO2 Array Nanotubes on Ti-6Al-4V Alloy

Background: The correlation between anodization conditions and the ageing effect on TiO2 nanotubes (TNT) surface has been widely studied in different media and conditions (physiological solutions, mechanical stresses in water, etc.) for the prediction of their behaviour over a long period of time. In the present study, the synthesized TiO2 nanotubes (TNT) from Ti-6Al-4V alloy, which were left unattended and exposed to environmental conditions (i.e., humidity and ambient temperature) for more than 4 years, were investigated to underline any important alteration/changes and ageing effects, on the surface morphology, the surface composition, and the electrochemical behaviour. The nanotubes were made in 2018 by anodization in different potentials (20V, 40V, 50V, and 60V) for different times (30 min, 60 min, 90 min, 150 min and 180 min) in an Ethylene Glycol solution for other purposes. Methods: For the surface morphology characterisation, electronic microscopy (SEM) was performed to depict any tendency with anodization conditions: potential and time. The comparison study between the obtained results and the SEM pictures taken on similar samples made and characterized under the same conditions in 2018, reveals a noticeable alteration in the morphology and a change in the TNT’s external diameter. Surface composition was checked using energy dispersive spectrometry (EDXS). The EDXS spectra analysis was realised to investigate the storage time impact on structure surface stability. A drastic decrease in the amount of oxygen was noticed on all of the surfaces where wettability measurements by contact angle were performed to confirm the latter. The verification of the hydrophobicity of TNT surfaces attested that all aged samples are hydrophobic in concordance with EDXS analysis and X-ray photoelectron spectroscopy (XPS). To affirm the surface modification during the storage duration and its impact on the electrical behaviour: cyclic voltammetry (CV), open circuit potential (OCP) measurements, and Tafel plots are undergone on the aged samples and compared with the freshly synthesised samples [1],[2]. The plotted CV curved as a function of the scan rate and the composition of the electrolyte showed a correlation between the different samples electrochemical behaviour and their surface morphologies as well as the existence of surface states for all samples. Results: From the previous characterisation, it was obvious that the sample prepared at 40V over 3 hours showed a remarkable electrochemical behaviour. The ageing effect is closely related to the anodization conditions. It was also noticed that the amount of water in the electrolyte solution EG played a contributing factor in the onset of ageing. High water content causes the formation of nanograss which have a non-negligible influence on the morphology. Conclusion: These results can open a new way for the optimization of the storage conditions according to anodization conditions (electrolyte, voltage, time, and temperature annealing) of this material as well as for the study of the life cycle of products made from TiO2 nanotubes. : Exposing nanotube surfaces to ambient conditions without taking any precautionary measures and without knowing their historical anodization conditions can cause drastic changes in the electrochemical behaviour of TNT. These changes affect considerably their function for different applications.

Investigation of Conditions for Preparation of Ordered Nanohole Arrays by Anodization of Iron Substrates with Depression Patterns

Ordered iron oxide nanohole arrays were fabricated by the anodization of iron substrates with depression patterns formed by Ar ion milling with alumina masks in an ethylene glycol electrolyte containing NH4F and H2O. It was found that the optimization of anodization voltage, NH4F and H2O concentrations in the electrolyte, and electrolyte temperature is necessary to achieve straight pore growth induced from the depression patterns in the depth direction. The optimization of the anodization conditions enabled the formation of ordered iron oxide nanohole arrays with aspect ratios exceeding 10. The resulting ordered iron oxide nanohole arrays with high aspect ratios are expected to be applied to various functional devices such as photocatalysts and solar cells.

Investigation of Surface Oxide Layer Structure to Improve Durability of Stainless Steels Under Humidified Hydrogen

Durability of low cost stainless steels, selected from the materials widely used in other applications, was investigated under humidified hydrogen of SOFC anode condition. JIS SUS430J1L exhibited higher resistance for water oxidation. The feature came mainly from the thin Cr-rich oxide layer covering the alloy uniformly with little defects or segregations. Under humidified H2 at 700oC, Mn migrated outward and the morphology changed. Durability of the alloy seems to depend on the inner side of the surface oxide layer. Although the Cr-rich oxide layer blocked outward diffusion of metal ions, the layer could not block inward diffusion of oxygen ion completely. Improvement of the durability is possible by controlling the thickness of the surface oxide layer by the pre-heat-treatment.

On the Operando Structure of Ruthenium Oxides during the Oxygen Evolution Reaction in Acidic Media.

In the search for rational design strategies for oxygen evolution reaction (OER) catalysts, linking the catalyst structure to activity and stability is key. However, highly active catalysts such as IrOx and RuOx undergo structural changes under OER conditions, and hence, structure-activity-stability relationships need to take into account the operando structure of the catalyst. Under the highly anodic conditions of the oxygen evolution reaction (OER), electrocatalysts are often converted into an active form. Here, we studied this activation for amorphous and crystalline ruthenium oxide using X-ray absorption spectroscopy (XAS) and electrochemical scanning electron microscopy (EC-SEM). We tracked the evolution of surface oxygen species in ruthenium oxides while in parallel mapping the oxidation state of the Ru atoms to draw a complete picture of the oxidation events that lead to the OER active structure. Our data show that a large fraction of the OH groups in the oxide are deprotonated under OER conditions, leading to a highly oxidized active material. The oxidation is centered not only on the Ru atoms but also on the oxygen lattice. This oxygen lattice activation is particularly strong for amorphous RuOx. We propose that this property is key for the high activity and low stability observed for amorphous ruthenium oxide.

Template-based synthesis of Co3O4 and Co3O4/SnO2 bifunctional catalysts with enhanced electrocatalytic properties for reversible oxygen evolution and reduction reaction

Porous cobalt (III) oxide (Co3O4) and mixed cobalt (III) oxide - tin oxide (Co3O4/SnO2) were prepared by a novel template-based hydrothermal method resulting in their spherical morphology as confirmed by thorough physico-chemical characterisation. Two oxides were systematically examined as bifunctional electrocatalysts for oxygen reduction (ORR) and evolution (OER) reaction in alkaline media by voltammetry with rotating disk electrode, electrochemical impedance spectroscopy, and chronoamperometry. Low-cost Co3O4 and Co3O4/SnO2 electrocatalysts showed excellent ORR performance with low onset and half-wave potential, low Tafel slope, and the number of exchange electrons near 4, comparable to the commercial Pt/C electrocatalyst. Low OER onset potential of 1.52 and 1.57 V was observed for Co3O4 and Co3O4/SnO2, respectively, with low charge transfer resistance under anodic polarization conditions. Finally, to test bifunctional activity and durability of the two electrocatalyst, switch OER/ORR test was carried out.

Catalyst‐Support Interactions in Zr2ON2‐Supported IrOx Electrocatalysts to Break the Trade‐Off Relationship Between the Activity and Stability in the Acidic Oxygen Evolution Reaction

AbstractThe development of highly active and durable Ir‐based electrocatalysts for the acidic oxygen evolution reaction (OER) is challenging because of the corrosive anodic conditions. Herein, IrOx/Zr2ON2 electrocatalyst is demonstrated, employing Zr2ON2 as a support material, to overcome the trade‐off between the activity and stability in the OER. Zr2ON2 is selected due to its excellent electrical conductivity and chemical stability, and the fact that it induces strong interactions with IrOx catalysts. As a result, IrOx/Zr2ON2 electrocatalysts exhibit outstanding OER performances, reaching an overpotential of 255 mV at 10 mA cm−2 and a mass activity of 849 mA mgIr−1 at 1.55 V (vs the reversible hydrogen electrode). The activity of IrOx/Zr2ON2 is maintained at 10 mA cm−2 for 5 h, while in contrast, IrOx/ZrN and an unsupported IrOx catalyst undergo drastic degradation. Combined experimental X‐ray analyses and theoretical interpretations reveal that the reduced oxidation state of Ir and the extended IrO bond distance in IrOx/Zr2ON2 effectively increase the activity and stability of IrOx by altering reaction pathway from a conventional adsorbate evolution mechanism to a lattice oxygen‐participating mechanism. These results demonstrate that it is possible to effectively reduce the Ir content in OER catalysts through interface engineering without sacrificing the catalytic performance.

Revealing the dynamic temperature of the cathode catalyst layer inside proton exchange membrane fuel cell by experimental measurements and numerical analysis

Temperature variation inside the cathode catalyst layer (CCL) is significant, which could greatly damage fuel cell performance and durability. However, limited by CCL microstructure and complex physicochemical processes, the knowledge regarding CCL dynamic temperature is indeed insufficient. Thus, this work integrates a pre-prepared thin-film microsensor into the fuel cell to measure CCL surface temperature under dynamic load. At the same time, an improved transient thermal model considering local mass transport and liquid effect on thermal contact resistance (TCR) is established for the first time to analyze the internal process. Results show that CCL temperature is greatly affected by local resistance and interface accumulated water. And, as confirmed by both experiment and simulation, the CCL surface exhibits 0–7 °C temperature variation, whose profile changes sharply at the beginning and then evolutes slowly, eventually taking tens or hundreds of seconds to reach a new steady state due to thermal inertia. Moreover, the temperature is further increased by ∼1 °C as cathode humidity increases or stoichiometric ratio decreases, but only slight changes with the anode condition. The significant role of cathode operation is attributed to the greater mass transfer resistance and more sensitive intrinsic oxygen reduction reaction to reactant change. This study is expected to provide a deeper understanding of CCL dynamic temperature, thus improving fuel cell thermal management.

The Influence of Preparation Parameters on Structural and Optical Properties of N-Type Porous Silicon

In this paper, we describe the formation of macroporous silicon (MPS) formed anodically polarized on n type Si (100) substrates at a constant current density under front side illumination using two electrolytes, HF/Ethanol and HF/Ethanol/H2O2. The effect of adding H2O2 in the solution on the resulting pores were investigated by scanning electron microscopy (SEM), infrared spectroscopy (FTIR), contact angle measurements and UV-vis spectrophotometry. The results showed that for the anodization conditions the MPS formed in peroxide based (H2O2)/HF/Ethanol solution exhibited structures with larger pore size and different pore morphologies depending on the etching time than those formed in HF/Ethanol. The pore density and the pore size of the MPS samples increased with the etching time. The infrared absorption spectrum (FTIR) carried out on the freshly prepared sample indicates that the MPS contains Si-Hx bonds which decrease with increasing the etching time. Finally, measurements of contact angle indicate that the formed MPS samples are highly hydrophobic.

Effect of anode conditions on the performance of direct borohydride–hydrogen peroxide fuel cell system

Direct borohydride–hydrogen peroxide fuel cells (DBHPFCs) are attractive power sources for space applications. Although the cathode conditions are known to affect the system performance, the effect of the anode conditions is rarely investigated. Thus, in this study, a DBHPFC system was tested under various anode conditions, such as electrocatalyst, fuel concentration, and stabilizer concentration, to investigate their effects on the system performance. A virtual DBHPFC system was analyzed based on the experimental data obtained from fuel cell tests. The anode electrocatalyst had a considerable effect on the mass and electrochemical reaction rate of the fuel cell system, but had minimal effect on the decomposition reaction rate. The NaBH4 concentration greatly influenced the mass and decomposition reaction rate of the fuel cell system; however, it had minimal impact on the electrochemical reaction rate. The NaOH concentration affected the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system. Therefore, the significant effects of the anode conditions on the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system prompt the need for their careful selection through fuel cell tests and system analysis.

Preparation of TiO2 Nanotube Arrays with Controllable Morphology and their Superhydrophobic Modification for Photocatalytic Degradation of Water Pollution

TiO2, as a photoactive semiconductor material, where like photocatalysis technology is a hot topic of research in recent years, shows great potential for application in the direction of environmental pollution treatment and solar-chemical energy conversion. In this paper, we prepared titanium dioxide nanotube arrays (TNAs) by a simple one-step anodic oxidation method in an ethylene glycol electrolyte containing ammonium fluoride under optimized conditions. The effects of anodic oxidation voltage, anodic oxidation time and annealing temperature on the growth of TNAs were systematically investigated. It was shown that the sample parameters of TNAs prepared by anodic oxidation were influenced by the anodic oxidation conditions, and the tube diameter and anodic oxidation voltage were positively correlated in a certain range. The TNAs with the best characterization performance were selected for photocatalytic degradation, and methylene blue (MB) was used to simulate the organic pollutants. The results show that TNAs have better photocatalytic activity compared with conventional TiO2. On the basis of this, stearic acid (SA) and TNAs were compounded and modified. The TNAs were made to obtain superhydrophobic properties. The photocatalytic degradation experiments were carried out on them. The results show that the superhydrophobic modification does not affect their photocatalytic activity, so it is possible to achieve photocatalytic degradation of water pollution under the premise of superhydrophobicity, which has greater application prospects in water pollution treatment.

Synthesis of aluminum telluride thin films via using electrodeposition method for solar absorber applications

In this work, aluminum telluride thin films were synthesized via using a systematically electrodeposited method at different applied anodic potentials (2–12 V) on conductive FTO glass substrates. As the aluminium sheet was used as a source of Al3+ cation and the Na2TeO3 solution produced Te2- anion. X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and ultraviolet–visible (UV) spectroscopy were employed to investigate the unique properties of the Al2Te3 thin films. The results reveal that the electrodeposited Al2Te3 films can be a good promising candidate for a solar absorber material or other optoelectronic applications through the analysis of structural, morphological, and optical properties with the significant evidence of the optimum applied anodic potential condition in the range of 8–12 V.

Effects of anodization conditions on subsequent hydride corrosion of uranium metal

Effects of anodization conditions on subsequent hydride corrosion of uranium metal

Extraction and transformation of elements in phosphogypsum by electrokinetics

Phosphogypsum (PG), as a typical industrial solid waste produced in the wet production process of phosphoric acid, is harmful to the environment and difficult to utilize. In order to explore the migration behavior of impurities in PG under electrokinetic treatment and provide a new treatment technology for the purification and harmless treatment, this paper studied the distribution of soluble impurities (PO43−, F−, Sr, Pb, Cr, Cu, and Mn) in PG under different electrokinetic treatment conditions. The results indicated that most of water-soluble impurities demonstrated obvious migration distribution laws at different voltages. Under the influence of electroosmotic flow, F− accumulated continually at the cathode. Positive MF+ was produced in acidic circumstances by combining F− and metal ions and travelled to the cathode under the combined action of electric field force and electroosmotic flow. Under electrokinetic treatment, the concentration of PO43− in the anode chamber increased while that of in the cathode chamber decreased. A large number of anions in PG were attached to the anode by coulomb force, reducing the potential. PO43− was s largely enriched in the anode chamber, which is controlled by the free diffusion effect of ions. Heavy metals exhibited higher leaching efficiency under anodic acid conditions. With the increase of applied voltage, the concentration of heavy metals in the anode chamber gradually increased, which was related to the activity of solution, pH and other factors. The above results indicate that electrokinetic treatment is a novel and efficient PG treatment technology, which has a broad application prospect in impurity removal and PG resource recovery.

Activation of stainless steel 316L anode for anion exchange membrane water electrolysis

The increased emphasis on renewable energy has resulted in a surge of R&D efforts into hydrogen and battery research. The intensive electrochemical environment surrounding the anodic oxygen evolution reaction (OER) has plagued both the activity and stability of the catalytic layer, substrate and porous transport layer, ultimately affecting both these industries. Herein, we report the benefits of potential cycling (PC) a 316L stainless steel felt porous transport layer (PTL) for use in anion exchange membrane water electrolysis. The PC increased surface roughness and created a CrFe5Ni2-OxHy layer through the oxidation of iron as shown by SEM, EDS, XPS, XRD and Raman spectroscopy. Post-PC tests in a three-electrode setup reveal a ≈ 68% decline in polarisation resistance, which is reflected in its performance when employed as an anode in an anion exchange membrane water electrolyser (AEMWE). Overall, potential cycling the PTL under anodic conditions resulted in an improved performance when tested in a AEMWE. Implementing this treatment on stainless steel anodes could be considered to achieve an improved AEMWE performance.

Effect of transcranialdirect current stimulation on the right brain temporal area on processing approach and avoidance attitudes with negation

Language describes approach/avoidance intentionality by means of attitudinal verbs (e.g., accept vs. reject). The right superior temporal sulcus (rSTS) has been shown to be recruited in processing action goals and approach intentionality in social contexts. In this study, we examine whether transcranial direct current stimulation (tDCS) of this area improves the processing of attitudinal verbs (either of approach or avoidance) in the context of affirmative and negative sentences [e.g., Julio (did not)/included meat on the grocery list]. After being subjected to tDCS, 46 participants were given sentences for passive reading. Sentences were displayed in segments with a fixed time of exposition, and a verb, either the one mentioned in the sentence or an alternative one was displayed 1,500 ms after the sentence (e.g., included vs. excluded, in the example). Participants were told to read them and then press the space bar to continue the experiment. Results showed shorter latencies for approach verbs that were either mentioned in approach sentences or the alternatives in avoidance sentences, both in affirmative and negative versions under anodal conditions compared to sham conditions. Thus, the anodal stimulation of rSTS affected the accessibility of approach verbs that were not modulated either by being mentioned or by sentence polarity. In addition, mentioned verbs had shorter reading times than the alternative ones in negative sentences in the anodal vs. sham condition. This suggests that stimulation caused an effect of negation in the activation of the mentioned verb. Implications are discussed in the context of the role of the rSTS in processing attitudinal verbs and negation to understand better approach and avoidance mediated by language in the framework of the two-step model of negation processing.

Understanding the effects of operating conditions on the water management in anion exchange membrane fuel cells

While water management in Anion Exchange Membrane Fuel Cells (AEMFCs) is seen as crucial for performance and durability, measurements of water management within operating cells remain few. In this work, we measured the performance of an H2/O2 AEMFC based on a low-density polyethylene membrane AEM, PtRu/C anode and Fe–N–C cathode for various combinations of inlet relative humidities, gas pressures and flow rates. Simultaneously, the anode and cathode outlet relative humidities were measured using humidity sensors, from which the amount of water removed from the cell could be quantified for each side. The data shows that back-diffusion of water from anode to cathode results in increasing outlet relative humidity with increased current density, both at anode and cathode. Water produced in the AEMFC was thus removed from both sides. The maximum current density was found to be strongly connected to anode flooding, which is also the main cause for hysteresis during potentiodynamic scans. However, under atypical operating conditions, the cell performance may also be limited by low humidity at the cathode, with associated low ionomer conductivity. Overall, it is concluded that water management of AEMFC with thin AEMs can be achieved by playing with both the anode and cathode operating conditions.

The Mechanism Regulating Film Thickness During Porous Anodic Oxide Growth on Aluminium: Transition from Homogeneously Thick Films During Soft Anodizing to Nodule Formation During Hard Anodizing

The growth of porous anodic film during sulphuric acid anodizing has been studied with the aim of investigating the mechanism resulting in uniform film thickness under conventional anodizing conditions and localized film growth under hard anodizing conditions. Based on the field-assisted flow model, it is proposed that the film comprises a rigid part, the cell walls, and a barrier layer plasticized by the combined effect of the electric field, the electrostriction stresses and the ionic migration process. Under conventional anodizing conditions, the film is uniform in thickness because the rigid part regulates the growth rate at the plasticized barrier layer by providing a mechanical connection between neighbouring pores, and hence a mechanical constraint. Vice versa, under hard anodizing conditions, cracking of the rigid part of the film due to rapid film growth rate leads to loss of the regulation mechanism provided by the mechanical constraint and hence localized film growth and formation of nodules.

Formation of adsorbent thin layer on aluminum sheet by using a silane coupling agent for vapor adsorption refrigeration system

Recently adsorbent coating technique was pointed for the aluminum fin in the ad/desorption chamber of an adsorption heat pump/chiller. This research proposes an aluminum substrate adsorbent coating method including examination of characteristics and adsorption isotherms. An aluminum substrate was dipped into the adsorbent-suspended solution to form a composite adsorbent layer on its surface. The adhesion of the adsorbents onto the aluminum substrate was evaluated by the peeling test. The aluminum oxide film on the aluminum substrate promotes the adhesion between adsorbent and aluminum substrate referring to the residual ratio. The suitable anodization condition of the aluminum oxide film is 150 volts for 2 min yielding the thin aluminum oxide film layer upon the aluminum substrate 67 nm of thickness. The suspended adsorbent solution was prepared at a mass ratio of 3 g-adsorbent g−1-coupling agent that provided the thickest adsorbent-coated layer by dip coating. Zeolite AQSOA-Z01 is a good choice to coat the aluminum substrate because it satisfied the adhesion strength and specific cooling capacity of 239.4 kJ kg−1 in the operating relative pressure range of adsorption heat pumps/chillers.

(Invited) Molecular Design for Reactive Redox Separations

This talk presents the rational molecular design of next-generation redox-active sorbents for the capture of carbon dioxide from dilute sources such as air. We discuss the electrochemical generation of organic nucleophiles (C and O-nucleophiles), with a focus on chemical species known to rapidly capture CO2 under cathodic conditions, and that release the bound CO2 under anodic conditions. We first introduce the thermodynamics of redox-reactive CO2-binder chemical space for electrochemical reactive capture and release of CO2 by electrochemically-generated nucleophiles. We then use this thermodynamic understanding to guide the synthetic development of new robust redox-reactive media for the capture of CO2 from dilute sources that take advantage of the beneficial bulk properties of ionic liquids and the well-established redox chemistries of reduced quinones.

Visualization of Hydrogen Penetration Generated in an Atmospheric Corrosion and a Crevice Corrosion

Hydrogen could form in the corrosion reaction and sometimes causes hydrogen-related deterioration of steel. Spatial distribution of hydrogen penetration in steels has been observed using a photocurrent mapping method. In this method, hydrogen penetrated from the backside of the steel sheet formed by the cathodic polarization or corrosion reaction causes an enhancement of photocurrent intensity under the photo-irradiation to the passive film in the anodic biased condition. This photocurrent enhancement may be provided by the photo-generated holes that oxidize hydrogen atoms efficiently on the passive film surface. This work conducted hydrogen penetration mapping using a photo-charge mapping method newly developed for rapid mapping measurement. In this method, a polarization current during single UV-light pulse irradiation was integrated to obtain the charge Q a, and then a charge Q b during the irradiation was subtracted to obtain a photo-charge Q PC = Q a-Q b for a single pulse. This process was performed by the electronics circuit controlled by the computer. Combination of pulse system and X-Y galvano-mirror-scanning device for a light beam emitted from pulse UV (405 nm, 0.2 W) pulse laser, rapid photocharge mapping was achieved, e.g., 24 s for 40 x 40 = 1600 pixel map. In the experiments, a Devanathan-type cell composed of a top cell of a humidity control room and a bottom electrochemical cell was constructed. A UV laser beam was induced to the bottom cell via a quartz window to scan the bottom iron surface. Fig. 1 shows an example of the time-transition of photocharge maps measured for an iron sheet. In the experiment, a droplet of NaCl solution was put on the surface, and the humidity of the top cell was changed to wet/dry/wet conditions. In the figure, a droplet grew with absorbing moisture at 48 ks, rust expanded and precipitated in the droplet at 131 ks, dried to form rust at 668 ks, and soaked again at 534 ks. In this process, penetration of hydrogen was observed at the bottom face. Initially, hydrogen appeared only at the center of the droplet and then expanded to the lateral direction by increasing the photocharge. Fig. 1. Time-transition of top images of an iron sheet (0.1 mmt) with a single NaCl solution droplet and photocharge maps measured for the bottom side of the iron sheet polarized at 0.7 V vs. Ag/AgCl in pH8.4 borate solution. Figure 1