and Martine Ulmann

Bio: and Martine Ulmann is an academic researcher from University of Geneva. The author has contributed to research in topics: Tungsten trioxide & Visible spectrum. The author has an hindex of 2, co-authored 2 publications receiving 1340 citations.

Crystallographically oriented mesoporous WO3 films: synthesis, characterization, and applications.

Abstract: Mesoporous semiconducting films consisting of preferentially orientated monoclinic-phase nanocrystals of tungsten trioxide have been prepared using a novel version of the sol−gel method. Transformations undergone by a colloidal solution of tungstic acid, stabilized by an organic additive such as poly(ethylene glycol) (PEG) 300, as a function of the annealing temperature have been followed by means of a confocal Raman microscope. The shape and size of WO3 nanoparticles, the porosity, and the properties of the films depend critically on preparation parameters, such as the tungstic acid/PEG ratio, the PEG chain length, and the annealing conditions. Well-crystallized WO3 films combine excellent photoresponse to the blue region of the solar spectrum, up to 500 nm, with good transparency at wavelengths larger than 550 nm. Particular applications of these nanocrystalline WO3 films include photoelectrochemical and electrochromic devices.

Photoelectrochemical Properties of Nanostructured Tungsten Trioxide Films

Abstract: The photoelectrochemical characteristics of highly transparent nanoporous WO3 films are described. The photocurrent versus excitation wavelength spectra of these photoelectrodes exhibit a maximum close to 400 nm and a significant photoresponse to the blue part of the visible spectrum. The observed conversion efficiencies attain 75% for the photogeneration of oxygen from 1 M aq HClO4 and reach 190% in the presence of methanol in the solution, denoting in the latter case the occurrence of a perfect photocurrent doubling. Experiments conducted under simulated solar AM 1.5 illumination resulted in steady-state anodic photocurrents of the order of several mA/cm2.

TiO2 nanotubes: synthesis and applications.

Abstract: TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

Solar Water Splitting: Progress Using Hematite (α‐Fe2O3) Photoelectrodes

Abstract: Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (α-Fe(2)O(3)) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion.

Inorganic nanostructures for photoelectrochemical and photocatalytic water splitting

Abstract: The increasing human need for clean and renewable energy has stimulated research in artificial photosynthesis, and in particular water photoelectrolysis as a pathway to hydrogen fuel. Nanostructured devices are widely regarded as an opportunity to improve efficiency and lower costs, but as a detailed analysis shows, they also have considerably disadvantages. This article reviews the current state of research on nanoscale-enhanced photoelectrodes and photocatalysts for the water splitting reaction. The focus is on transition metal oxides with special emphasis of Fe2O3, but nitrides and chalcogenides, and main group element compounds, including carbon nitride and silicon, are also covered. The effects of nanostructuring on carrier generation and collection, multiple exciton generation, and quantum confinement are also discussed, as well as implications of particle size on surface recombination, on the size of space charge layers and on the possibility of controlling nanostructure energetics via potential determining ions. After a summary of electrocatalytic and plasmonic nanostructures, the review concludes with an outlook on the challenges in solar fuel generation with nanoscale inorganic materials.

Novel Carbon-Doped TiO2 Nanotube Arrays with High Aspect Ratios for Efficient Solar Water Splitting

Abstract: The photocatalytic splitting of water into hydrogen and oxygen using solar light is a potentially clean and renewable source for hydrogen fuel.1,2 There has been extensive investigation into metal-oxide semiconductors such as TiO2, WO3, and Fe2O3, which can be used as photoanodes in thin-film form.3-5 Of the materials being developed for photoanodes, TiO2 remains one of the most promising because of its low cost, chemical inertness, and photostability.6 However, the widespread technological use of TiO2 is hindered by its low utilization of solar energy in the visible region. In this study, we report the preparation of vertically grown carbon-doped TiO2 (TiO2-xCx) nanotube arrays with high aspect ratios for maximizing the photocleavage of water under white-light irradiation. The synthesized TiO2-xCx nanotube arrays showed much higher photocurrent densities and more efficient water splitting under visible-light illumination (> 420 nm) than pure TiO2 nanotube arrays. The total photocurrent was more than 20 t...

Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications

Abstract: Metal oxides are the key ingredients for the development of many advanced functional materials and smart devices. Nanostructuring has emerged as one of the best tools to unlock their full potential. Tungsten oxides (WOx) are unique materials that have been rigorously studied for their chromism, photocatalysis, and sensing capabilities. However, they exhibit further important properties and functionalities that have received relatively little attention in the past. This Feature Article presents a general review of nanostructured WOx, their properties, methods of synthesis, and a description of how they can be used in unique ways for different applications. Tungsten oxides (WOx) are unique functional materials that can be obtained in a vast variety of nanostructured forms. This Feature Article presents a comprehensive review on the properties of WOx that goes beyond chromism and photocatalysis, for which they are usually investigated for. This is followed by a survey of their synthesis methods and implementations for different applications.