The influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNS N08031 stainless steel in a contaminated phosphoric acid solution were evaluated. ...Stabilisation of the passive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemical impedance spectroscopy (EIS) measurements, Mott–Schottky analysis and X-ray photoelectron spectroscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The film formed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed the presence of fluoride ions.
The passive and transpassive behaviour of Alloy 31, a highly alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine solution (400g/l) at 25°C using ...potentiostatic polarisation combined with electrochemical impedance spectroscopy and Mott–Schottky analysis. The passive film formed on Alloy 31 has been found to be p-type and/or n-type in electronic character, depending on the film formation potential. The thickness of the film formed at potentials within the passive region increases linearly with applied potential. The film formed at transpassive potentials is thinner and more conductive than the film formed within the passive region. These observations are consistent with the predictions of the Point Defect Model for passive and transpassive films on metals and alloys.
In this work, CuOx (x = 1 and 2) nanostructures have been synthesized by electrochemical anodization in ethylene glycol based electrolytes using oxalic acid or NaF (with or without NaOH) as ...complexing agents. The influence of hydrodynamic conditions and time during anodization of copper have also been evaluated. A comprehensive morphological, structural, electrochemical and photoelectrochemical characterization of the nanostructures has been performed. The results revealed the convenient use of oxalic acid and 250 rpm for 5 minutes during electrochemical anodization to obtain homogeneous CuOx nanostructures formed by spheres with Cu2O as a predominant phase. Using this nanostructure as a photocathode for N2O photoelectron-reduction, almost 100% of N2O removal was achieved after 1 h, showing the improvement of the photoelectrochemical approach vs. the photo or the electro performance.
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•Annealing in argon and nitrogen atmospheres increase oxygen vacancies formation.•Nitrogen atoms appear in the matrix of the crystalline TiO2 annealed in nitrogen.•Band gap of ...nanostructures decreases annealing in non-oxidizing atmospheres.•Nitrogen or argon atmospheres increases the photocatalytic activity of nanotubes.
The influence of three annealing atmospheres (air, nitrogen and argon) and the use of controlled hydrodynamic conditions (from 0 to 5000 rpm) on morphological, structural, chemical and photoelectrochemical properties of TiO2 nanotubes have been evaluated. For this purpose, different characterization techniques have been used: Field Emission Scanning Electron Microscopy, Raman Confocal Laser Spectroscopy, X-Ray Diffraction, X-Ray Photoelectron Spectroscopy, Incident Photon-to-electron Conversion Efficiency measurements, ultraviolet–visible absorption spectra, Mott-Schottky analysis and photoelectrochemical water splitting tests. According to the results, it can be concluded that both hydrodynamic conditions and annealing in non-oxidizing atmospheres improve the photoelectrochemical response of the TiO2 nanotubes. This fact has been attributed to the oxygen vacancies formed after annealing in argon and nitrogen atmospheres and also to the presence of nitrogen into the TiO2 lattice due to the thermal treatment in the nitrogen atmosphere.
In this study, hybrid ZnO-TiO2 nanostructures have been synthesised by means of a simple electrochemical anodisation of titanium and subsequently ZnO electrodeposition. The influence of Zn(NO3)2 ...concentration and temperature during the electrodeposition process was evaluated. Different techniques were used to analyse the synthesised nanostructures, notably Field Emission Scanning Electron Microscopy (FE-SEM) with Energy-dispersive X-ray spectroscopy (EDX) and Confocal Microscopy with Raman spectroscopy coupled with an Atomic Force Microscope. Photoelectrochemical water splitting tests were also performed at the hybrid nanostructures. According to the results, the photoelectrochemical response of the specimens increases with the addition of ZnO, besides the hybrid nanostructures obtained at 25 °C and using a Zn(NO3)2 concentration of 1 mM showed photocurrent densities 80% higher than the ones obtained for TiO2 nanotubes. Analysis of Variance of the data confirms the obtained results.
•TiO2-ZnO nanostructures were obtained by anodization of Ti and ZnO electrodeposition.•Electrodeposition was performed with different temperatures and amounts of Zn(NO3)2.•Higher photocurrents are obtained with lower Zn(NO3)2 concentrations and temperatures.•Temperature and interaction between it and Zn(NO3)2 are statistically significant.
Hybrid TiO2-WO3 nanostructures has been synthesized by electrochemical anodization under controlled hydrodynamic conditions followed by electrodeposition in the presence of different contents of ...Na2WO4 (5, 15 and 25 mM) and H2O2 (20, 30 and 40 mM). The influence of the electrolyte used for electrodeposition on the morphology, crystalline structure and photoelectrochemical response for water splitting has been evaluated through Field Emission Electronic Microscopy, High-Resolution Transmission Electron Microscopy, Confocal Raman Spectroscopy, Grazing Incidence X Ray Diffraction, X-Ray Photoelectron Spectroscopy, Atomic Force microscopy and photocurrent versus potential measurements. Additionally, a statistical multi-factor categorical analysis was performed to determine the most significant influential parameters. Results show that hybrid TiO2-WO3 nanostructures formed by simple anodization and subsequent electrodeposition with 30 mM H2O2 and 25 mM Na2WO4 present the highest photocurrent response, 60% higher if compared to TiO2 anodized nanotubes, solving the main problems presented during the usual fabrication of heterostructures, i.e. high temperatures, pressures, number of chemicals and time.
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•TiO2-WO3 nanostructures were synthesized by anodization followed by electrodeposition.•Different H2O2 and Na2WO4 concentrations were used for electrodeposition.•Interaction between Na2WO4 and H2O2 concentrations is statistically significant.•Nanostructures synthesized with 30 mM H2O2 were the best photocatalysts.•An increase in the photocurrent of 50–60% with respect to the TiO2 nanotubes was obtained.
► Impedance parameters vary depending on the applied potential of film formation. ► Protective properties were observed to increase with formation potential up to 0.8V. ► The proximity of ...transpassive region affected to the stability of the passive film. ► Mott–Schottky plots showed the semiconductive properties of Alloy 31.
The electrochemical behaviour of the highly alloyed austenitic stainless steel UNS N08031 (Alloy 31) in a contaminated phosphoric acid solution is studied using potentiodynamic curves, EIS and Mott–Shottky. The relative stability of the films formed on Alloy 31 has been studied after a pre-passivated treatment at 0.3, 0.5, 0.8 and 1VAg/AgCl, potentials within the passive domain. The protection of Alloy 31 was provided by the inner oxide film, while the outer film was more defective. The electronic-semiconducting properties of the passive films have been correlated to corrosion resistance. Passivated Alloy 31 at 0.8VAg/AgCl showed lower concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.
► The CPT transition was between 100 and 125
°C. ► Studied materials repassivated after the breakdown of the passive film even at 150
°C. ► Corrosion current densities increased with temperature ...following the Arrhenius equation. ► The pitting corrosion resistance of materials decreases with temperature. ► Temperature makes passivation of metals and repassivation of pits difficult.
Pitting corrosion resistance and galvanic behaviour of Alloy 31, a highly alloyed austenitic stainless steel (UNS N08031), and its weldment were studied in a heavy brine LiBr solution 1080
g/l at different temperatures (75–150
°C) using electrochemical techniques. The Mixed Potential Theory was used to evaluate the galvanic corrosion between the base and welded metals. Cyclic potentiodynamic curves indicate that high temperatures make passivation and repassivation of pits difficult, because the whole passivation range and the repassivation potential values decrease with temperature. The critical pitting transition occurs between 100 and 125
°C.
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•TiO2 nanostructures doped after annealing improve photocurrent (ip) response.•The ip improvement is a combination of traps passivation and electrical conductivity.•The stability of ...Li+ insertion after annealing was checked.•TiO2 nanostructures doped after annealing are stable against photocorrosion.
Different TiO2 nanostructures, nanotubes and nanosponges, were obtained by anodization of Ti under stagnant and hydrodynamic conditions. Samples were doped with Li+ before and after annealing at 450°C during 1h. The nanostructures were characterized by different microscopy techniques: Field Emission Scanning Electron Microscopy (FE-SEM) and Raman Confocal Laser Microscopy. Additionally, Incident Photon-to-electron Conversion Efficiency (IPCE), photoelectrochemical water splitting and stability measurements were also performed. According to the results, TiO2 nanostructures doped before annealing present the worst photocurrent response, even if compared with undoped samples. On the other hand, this study reveals that Li+-doped TiO2 nanostructures doped after annealing can be used as durable and stable photoanodes for photoelectrochemical water splitting applications.
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•Hydrodynamic conditions during anodization remove part of the initiation layer.•Hydrodynamic conditions during anodization led to higher photocurrent densities.•The conductivity of ...the NTs increases with Li+ intercalation.•There is a synergistic effect among the hydrodynamic conditions and Li+ intercalation.•Doped nanotubes were stable in the test electrolyte under illumination.
This work studies the influence of using hydrodynamic conditions (Reynolds number, Re=0 to Re=600) during Ti anodization and Li+ intercalation on anatase TiO2 nanotubes. The synthesized photocatalysts were characterized by using Field Emission Scanning Electron Microscope (FE-SEM), Raman Confocal Laser Microscopy, Electrochemical Impedance Spectroscopy (EIS), Mott-Schottky analysis (M-S), photoelectrochemical hydrogen production and resistance to photocorrosion tests. The obtained results showed that the conductivity of the NTs increases with Li+ intercalation and Re. The latter is due to the fact that the hydrodynamic conditions eliminate part of the initiation layer formed over the tube-tops, which is related to an increase of the photocurrent in the photoelectrochemical water splitting. Besides, the photogenerated electron-hole pairs are facilitated by Li+ intercalation. Finally, this work confirms that there is a synergistic effect between Re and Li+ intercalation.
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