Photoelectrochemical Properties of Anodic TiO2 Nanosponge Layers

In the present work we grow TiO2 nanosponge structures by anodizing Ti in a glycerol/water/NH4F electrolyte to thickness of some mu m. We evaluate the photoelectrochemical behavior (bandgap, photocurrent-voltage characteristics) in presence and absence of methanol. Methanol drastically affects the photoresponse (due to hole capture and current doubling). The optimum thickness for photoelectrochemical applications of these nanostructures is dependent on the excitation wavelength. For applications such as solar light water splitting, anodic sponge structure of approximate to 500 nm thickness can be beneficially used to increase the photoresponse compared to compact TiO2 layers.The authors would like to express their gratitude to the Spanish Ministry of Science and Innovation FPU grant given to Rita Sanchez Tovar, as well as DFG, and the DFG Cluster of Excellence (EAM) at the University of Erlangen-Nuremberg for financial support.Sánchez Tovar, R.; Lee, K.; Garcia-Anton, J.; Schmuki, P. (2013). Photoelectrochemical Properties of Anodic TiO2 Nanosponge Layers. ECS Electrochemistry Letters. 2(3):9-11. doi:10.1149/2.005303eelS9112

Photoelectrochemical characterization of anatase-rutile mixed TiO2 nanosponges

This work studies the influence of using hydrodynamic conditions during anodization on the morphology and electrochemical properties of anatase/rutile mixed TiO2 nanotubes (Reynolds number, Re = 0) and nanosponges (Re > 0). To this purpose different techniques were used, such as: microscopy techniques (Field-Emission Scanning Electron Microscope, FE-SEM, and Confocal Laser-Raman Spectroscopy), Electrochemical Impedance Spectroscopy (EIS), Mott Schottky (MS) analysis and photoelectrochemical water splitting tests. This investigation demonstrates that the morphology of TiO2 nanostructures may be greatly affected due to the hydrodynamic conditions and it can be adjusted in order to increase the efficiency for energy and environmental applications

Effect of Temperature on Galvanic Corrosion of Non-Welded/Welded AISI 316L Stainless Steel in H3PO4

[EN] Galvanic corrosion of non-welded/welded AISI 316L SS at different temperatures (25 degrees C to 60 degrees C) at a Reynolds number of 1456 in phosphoric acid has been studied using polarization curves (by the mixed potential theory) and zero resistance ammeter (ZRA) measurements. Imposed potential measurements provide more active predicted coupled potentials and higher Galvanic current densities than those obtained using ZRA measurements. Polarization curves show that the anode of the pair is the non-welded AISI 316L. Galvanic current density values obtained from polarization curves increase with temperature. ZRA tests present the highest i(G) values at 60 degrees C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluate the Galvanic phenomenon importance. Both techniques present the most positive potentials at the highest temperature.The authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/018046/08).Sánchez Tovar, R.; Montañés, M.; Garcia-Anton, J.; Guenbour, A. (2010). Effect of Temperature on Galvanic Corrosion of Non-Welded/Welded AISI 316L Stainless Steel in H3PO4. ECS Transactions. 25(37):63-81. https://doi.org/10.1149/1.3407548S6381253

The case method: study of a corrosion problem

[EN] The aim of the present work is the application of the case method as teaching-learning methodology for the study of a corrosion problem, in order to obtain more active learning of the student. The educational innovation has been applied in 2018/2019 academic year in the subject of “Manufacturing Processes of Building Materials” imparted in the fourth course of the Chemical Engineering Degree in the Higher Technical School of Industrial Engineering in the Polytechnic University of Valencia. Such educational innovation consists in the description by the lecturer of a real situation about a corrosion problem, so that the students can analyse it and propose solutions individually and in group. At the end of the case it is added questions to help to the students in the analysis. This activity is realized in class, which is evaluated using a rubric. The evaluation of the educational innovation proposed is realized by the scores of the students, the polls of the students, and the autoevaluation of the lecturer. The results show the high scores obtained by the students in the case method and the high grade of satisfaction of the students after applying the educational innovation. The case method permits that the students know real situations that they could find in a professional future, which increase the motivation towards the subject of study.Authors would like to express their gratitude to the project PIME: Aprendizaje Basado en Problemas para su aplicación en las áreas de Ingeniería Química y de Materiales (Ref. 27) and to the Instituto de Ciencias de la Educación and the Vicerrectorado de Estudios, Calidad y Acreditación from the Universitat Politècnica de Valencia, for their financial and technical support.Muñoz Portero, MJ.; Sánchez Tovar, R.; Fernández Domene, RM. (2020). The case method: study of a corrosion problem. Editorial Universitat Politècnica de València. 249-257. https://doi.org/10.4995/INN2019.2019.10137OCS24925

Influence of the Flowing Conditions on the Galvanic Corrosion of the Copper/AISI 304 Pair in Lithium Bromide Using a Zero-Resistance Ammeter

[EN] In this work, the influence of Reynolds number (Re) on the galvanic corrosion of the copper/AISI 304 stainless steel pair in an 850 g/L lithium bromide solution was evaluated in a hydraulic circuit using a zero-resistance ammeter; this technique has the advantages that it can be used without disturbing the system under investigation and in continuous-time. Results show that copper is the anodic member of the pair for all the Re analyzed. The galvanic current density values are always greater under flowing than under stagnant conditions. A general tendency of galvanic current density to decrease with time is observed due to the formation of a film of corrosion products on copper surface. Under flowing conditions, initially, galvanic current density increases with Re; however, with time, this tendency is reversed. As Re increases, greater quantities of corrosion products are initially produced and, as a result, a thicker film is formed.This work was supported by the MICINN (reference number: CTQ2009-07518) and FEDER (Fondo Europeo de Desarrollo Regional). The authors also wish to express their gratitude to Asunción Jaime for her translation assistance.Montañés, M.; Sánchez Tovar, R.; Garcia-Anton, J.; Pérez-Herranz, V. (2010). Influence of the Flowing Conditions on the Galvanic Corrosion of the Copper/AISI 304 Pair in Lithium Bromide Using a Zero-Resistance Ammeter. INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE. 5(12):1934-1947. http://hdl.handle.net/10251/98931S1934194751

Influence of temperature and hydrodynamic conditions on the corrosion behavior of AISI 316L stainless steel in pure and polluted H3PO4: Application of the response surface methodology

Phosphoric acid is mainly produced by the wet acid process, where corrosion problems could be intensified due to the presence of impurities in the phosphate ores. Operating temperatures and flowing conditions aggravate the aforementioned problems. This work studies the influence of temperature (25-60 degrees C) and hydrodynamic conditions (Reynolds numbers from 1456 to 5066) on the corrosion of AISI 316L stainless steel in pure and polluted phosphoric acid solutions, by means of cyclic potentiodynamic polarization curves in a hydrodynamic circuit. The effect of temperature is the same as that caused by impurities, that is, higher corrosion rates and hindered passivation and repassivation resistance of the alloy. Statistical analysis by means of surface response methodology proved that the effect of temperature on the corrosion parameters of AISI 316L is more influential than the Reynolds number effect. The Reynolds number seems to have no significant influence on the corrosion behavior of stainless steel. Furthermore, the influence of temperature on the corrosion rate is much higher than on the rest of the corrosion parameters analyzed, especially in polluted phosphoric acid solutions. AISI 316L stainless steel has a clear interest for the phosphoric acid industry as a component material of some equipment due to its good corrosion properties at the different temperatures and Reynolds numbers studied even in polluted media. (C) 2012 Elsevier B.V. All rights reserved.The authors would like to express their gratitude to the Spanish MAEC (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09, D/030177/10), to the FPU grant given to Rita Sanchez Tovar, to the Generalitat Valenciana for its help in the CLSM acquisition (MY08/ISIRM/S/100) and to Dr. Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; Garcia-Anton, J.; Guenbour, A. (2012). Influence of temperature and hydrodynamic conditions on the corrosion behavior of AISI 316L stainless steel in pure and polluted H3PO4: Application of the response surface methodology. Materials Chemistry and Physics. 133(1):289-298. https://doi.org/10.1016/j.matchemphys.2012.01.024S289298133

Formation of ZnO nanowires by anodization under hydrodynamic conditions for photoelectrochemical water splitting

The present work studies the influence of hydrodynamic conditions (from 0 to 5000 rpm) during Zn anodization process on the morphology, structure and photoelectrocatalytic behavior of ZnO nanostructures. For this purpose, analysis with Confocal Laser-Raman Spectroscopy, Field Emission Scanning Electron Microscope (FE-SEM) and photoelectrochemical water splitting tests were performed. This investigation reveals that hydrodynamic conditions during anodization promoted the formation of ordered ZnO nanowires along the surface that greatly enhance its stability and increases the photocurrent density response for water splitting in a 159% at the 5000 rpm electrode rotation speed

Improvement in photocatalytic activity of stable WO3 nanoplatelet globular clusters arranged in a tree-like fashion: Influence of rotation velocity during anodization

This study investigates the influence of controlled hydrodynamic conditions during anodization of tungsten (W) on the morphological, electrochemical and photocatalytic properties of a novel WO3 nanostructure: globular clusters of nanoplatelets associated in a tree-like fashion. For this purpose different techniques such as Field-Emission Scanning Electronic Microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS) measurements, Mott-Schottky (M-S) analysis and photoelectrochemical water splitting tests have been carried out. Photoanodes obtained at 375 rpm showed the best photoresponse, much higher than that of conventional WO3 nanoplatelets, which can be ascribed to a noteworthy increase in the electrochemically active surface area leading to improved charge transfer at the interface. Moreover, the improved WO3 nanostructure displayed very good long-term photostability when irradiated with AM 1.5 illumination, thus solving the recurrent problem of the poor stability of WO3 against photodegradation processes

Influence of electrolyte temperature on the synthesis of iron oxide nanostructures by electrochemical anodization for water splitting

Iron oxide nanostructures are an attractive option for being used as photocatalyst in photoelectrochemical applications such as water splitting for hydrogen production. Nanostructures can be obtained by different techniques, and electrochemical anodization is one of the simplest methods which allows high control of the obtained morphology by controlling its different operational parameters. In the present study, the influence of the electrolyte temperature during electrochemical anodization under stagnant and hydrodynamic conditions was evaluated. Temperature considerably affected the morphology of the obtained nanostructures and their photoelectrochemical behavior. Several techniques were used in order to characterize the obtained nanostructures, such as Field Emission Scanning Electron Microscopy (before and after the annealing treatment in order to evaluate the changes in morphology), Raman spectroscopy, photocurrent vs. potential measurements and Mott-Schottky analysis. Results revealed that the nanostructures synthesized at an electrolyte temperature of 25 °C and 1000 rpm are the most suitable for being used as photocatalysts for water splitting

Formation of hematite nanotubes by two-step electrochemical anodization for efficient degradation of organic pollutants

Nowadays, hematite (a-Fe2O3) has emerged as a promising photocatalyst for efficient degradation of organic pollutants due to its properties such as suitable band-gap (~2.1 eV), stability against photocorrosion, abundance and low cost. However, some drawbacks such as low carrier mobility and short hole diffusion length limit its efficiency. In order to overcome these issues, self-ordered nanotubes can be synthetized. Anodization is one of the simplest and most economic techniques to produce nanostructures with high control. In the present study, self-ordered hematite nanotubes were synthetized by two-step electrochemical anodization. In two-step anodization, a first-step was actually a pretreatment to form well-ordered nanoporous template in which well-ordered nanotubes are grown by a second-step. The formed nanotubes were characterized by different methods such as Field Emission Scanning Microscopy and Raman spectroscopy to determine their morphology and crystalline structure, respectively. Furthermore, the obtained nanotubes were characterized by means of photocurrent density versus potential measurements (water splitting) to evaluate their efficiency as photocatalyst. Good results were obtained as the achieved photocurrent density was 0.079mA cm-2 at 0.58 V (vs. Ag/AgCl), which indicates that the nanotubes synthetized by two-step anodization aresuitable photocatalysts for degradation of organic pollutants