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

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

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 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

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

Iron oxide nanostructures for photoelectrochemical applications: Effect of applied potential during Fe anodization

In photoelectrochemistry, a suitable photoanode leading to high efficiencies in photocatalytic processes is a research challenge. Iron oxide nanostructures are promising materials to be used as photoanodes. In this work, different potentials during iron anodization were applied to study the properties of the synthesized nanostructures. Results revealed that nanostructures anodized at 50 V presented well-defined nanotubular structures with open-tube tops, and they achieved values of photocurrent density of 0.11 mA cm−2 at 0 rpm and 0.14 mA cm−2 at 1000 rpm (measured at 0.50 VAg/AgCl), corresponding to the oxygen evolution reaction from water, i.e. 2H2O + 4 h+ → 4H+ + O2, demonstrating their good photoelectrochemical behavior

Influence of the Heating Rate on the Annealing Treatment of Iron Oxide Nanostructures Obtained by Electrochemical Anodization under Hydrodynamic Conditions

Iron oxide nanostructures are promising materials for photoelectrochemical applications such as water splitting. In this work, electrochemical anodization of iron is used to form different iron oxide nanostructures, and the influence of different anodization parameters was studied in order to find the most suitable nanostructure for photocatalysis applications. On the one hand, hydrodynamic conditions were evaluated by stirring the electrode at different rotation speeds during the electrochemical anodization to check their influence on the formation of the nanostructures. On the other hand, different heating rates during the annealing treatment were studied for obtaining efficient iron oxide nanostructures. The synthesized nanostructures were characterized by different techniques such as photocurrent density vs. potential measurements, Field Emission Scanning Electron Microscopy, Raman spectroscopy and Incident Photon-toelectron Conversion Efficiency (IPCE). The results revealed that the best heating rate during the annealing treatment is 15 ºC·min-1 and that the hydrodynamic conditions allow the formation of nanotubular iron oxide structures achieving ~0.1 mA·cm-2 at 0.5 V (vs. Ag/AgCl) in the water splitting measurements. Moreover, all the nanostructures are mainly composed by hematite (α-Fe2O3) with some amount of magnetite (Fe3O4) in their structure. Finally, the IPCE measurements showed that the best rotation speed during the electrochemical anodization for the formation of an efficient iron oxide nanostructure for photocatalysis applications is 1,000 rpm