Showing papers on "Photoelectrolysis published in 2008"

Oxidation and Photo-Oxidation of Water on TiO2 Surface

Abstract: The oxidation and photo-oxidation of water on the rutile TiO2(110) surface is investigated using density functional theory (DFT) calculations. We investigate the relative stability of different surface terminations of TiO2 interacting with H2O and analyze the overpotential needed for the electrolysis and photoelectrolysis of water. We found that the most difficult step in the splitting of water process is the reaction of a H2O molecule with a vacancy in the surface to form an adsorbed hydroxyl group (OH*). Comparison to experiment shows that the computed overpotential for O2 evolution (0.78 V) is available under the experimental conditions required for both oxygen and hydrogen evolution.

Metal oxide photoanodes for solar hydrogen production

Abstract: The development of sustainable hydrogen production is a key target in the further facilitation of a hydrogen economy. Solar hydrogen generation through the photolytic splitting of water sensitised by semiconductor materials is attractive as it is both renewable and does not lead to problematic by-products, unlike current hydrogen sources such as natural gas. Consequently, the development of these semiconductor materials has undergone considerable research since their discovery over 30 years ago and it would seem prescient to review the more practical results of this research. Among the critical factors influencing the choice of semiconductor material for photoelectrolysis of water are the band-gap energies, flat band potentials and stability towards photocorrosion; the latter of these points directs us to focus on metal oxides. Careful design of thin films of photocatalyst material can eliminate potential routes of losses in performance, i.e., recombination at grain boundaries. Methods to overcome these problems are discussed such as coupling a photoanode for photolysis of water to a photovoltaic cell in a “tandem cell” device.

Light, water, hydrogen : the solar generation of hydrogen by water photoelectrolysis

Abstract: From Hydrocarbons to Hydrogen: Towards a Sustainable Future.- Hydrogen Generation by Water Splitting.- Photoelectrolysis.- Oxide Semiconducting Materials as Photoanodes.- Oxide Semiconductors Nano-Crystalline Tubular and Porous Systems.- Oxide Semiconductors: Suspended Nanoparticle Systems.- Non-Oxide Semiconductor Nanostructures.- Photovoltaic - Electrolysis Cells.

Photoelectrochemical and water photoelectrolysis properties of ordered TiO2 nanotubes fabricated by Ti anodization in fluoride-free HCl electrolytes

Abstract: Described is the synthesis of TiO2 nanotube array films by anodization of Ti foil in HCl electrolytes containing different H2O2 concentrations. Highly ordered nanotube arrays up to 860 nm in length, 15 nm inner pore diameter, and 10 nm wall thickness were obtained for one hour anodizations using a 0.5 M HCl aqueous electrolyte containing 0.1–0.5 M H2O2 concentrations for anodization potentials between 10–23 V. The use of ethylene glycol as the electrolyte medium significantly alters the anodization kinetics and resulting film morphologies; nanotube bundles several microns in length achieved for anodization potentials between 8 V and 18 V in only a few minutes. The nanotube arrays obtained from the ethylene glycol electrolytes show relatively higher photocurrents, ≈0.8 mA cm−2 under AM 1.5. Under 100 mW cm−2 AM 1.5 illumination a 500 °C annealed 1 cm2 nanotube array sample, obtained by anodization of a Ti foil sample in ethylene glycol + 0.5 M HCl + 0.4 M H2O2 electrolyte, demonstrates a hydrogen evolution rate of approximately 391 μL h−1 by water photoelectrolysis, time-power normalized evolution rate of 3.9 mL W−1 h−1, with water splitting confirmed by the 2 : 1 ratio of evolved hydrogen to oxygen.

Combinatorial Discovery and Optimization of a Complex Oxide with Water Photoelectrolysis Activity

Abstract: A ternary oxide containing cobalt, aluminum, and iron and not previously known to be active for the photoelectrolysis of water was identified using a high throughput combinatorial technique. The technique involves ink jet printing overlapping patterns of oxide precursors onto fluorine-doped tin oxide conductive glass substrates. Subsequent pyrolysis yields patterns of mixed oxide compositions that were screened for photoelectrolysis activity by scanning a laser over the material while it was immersed in an electrolyte and mapping the photocurrent response. The composition and optimum thickness for photoelectrochemical response of the newly identified material was further refined using quantitative ink jet printing. Chemical analysis of bulk and thin film samples revealed that the material contains cobalt, aluminum, and iron in a Co3O4 spinel structure with Fe and Al substituted into Co sites with a nominal stoichiometry of Co3−x−yAlxFeyO4 where x and y are about 0.18 and 0.30, respectively. The material i...

A General Method for the Anodic Formation of Crystalline Metal Oxide Nanotube Arrays without the Use of Thermal Annealing

Abstract: Valve metal oxides are versatile in their range of applications, which include high-K dielectrics, gas sensing, biomedical implants, field emitters, and photovoltaic cells. It is now generally recognized that nanoscale control of metal oxide architectures permits significant enhancement of the properties utilized in the above applications. In particular, TiO2 nanotube arrays formed by anodization have demonstrated outstanding performance in gas sensing, photocatalytic, and photovoltaic applications. Review papers on the subject are available. To date, amorphous nanotube arrays have been synthesized by Ti anodization with an elevated-temperature heat treatment, with temperatures typically greater than 350 8C being required to induce crystallinity. With regard to photoelectrochemical water splitting using thick-film Ti foil samples, annealing at temperatures sufficient to induce crystallinity usually leads to the formation of a thick barrier layer, separating the nanotube-array film from the underlying metal substrate, where recombination losses can occur. This barrier layer acts to hinder electron transfer to themetal electrode (cathode) where water reduction takes place, in turn reducing the overall water-splitting efficiency. The need for high-temperature crystallization limits nanotube array use with temperaturesensitive materials, such as polymers, for applications such as photocatalytic membranes. Therefore, low-temperature synthetic routes, where a high-temperature annealing step for crystallization is not required, are needed to obtain the full

Efficient Photoelectrolysis of Water using TiO2 Nanotube Arrays by Minimizing Recombination Losses with Organic Additives

Abstract: Electron−hole (e-h) recombination loss is a major practical problem in using TiO2 as a photocatalyst. This paper describes the use of organic additives to reduce e-h recombination losses which significantly improved the photocurrent density of the integrated TiO2 nanotube/Ti photoanode. Studies on photoelectrochemical hydrogen generation using nanotubular arrays of TiO2 photoanodes were carried out in 1 M KOH with the addition of three different organic additives, namely, methanol (one hydroxyl group), ethylene glycol (two hydroxyl groups), and glycerol (three hydroxyl groups) using a simulated solar light. Ethylene glycol was found to be the best among the investigated organic additives to reduce electron hole recombination. The addition of ethylene glycol produced a photocurrent density of 3.3 mA/cm2 at 0.2 VAg/AgCl compared to 0.87 mA/cm2, using a 87 mW/cm2 light intensity in 1 M KOH solution. On the other hand, methanol and glycerol showed a photocurrent density of 2.43 and 2.55 mA/cm2 under the same ...

Photoelectrolysis of water using heterostructural composite of TiO2 nanotubes and nanoparticles

Abstract: Efficient photoelectrolysis of water to generate hydrogen (H2) can be carried out by designing photocatalysts with good absorption as well as charge transport properties. One dimensional (1D), self-organized titania (TiO2) nanotubes are known to have excellent charge transport properties and TiO2 nanoparticles (NPs) are good for better photon absorption. This paper describes the synthesis of a composite photocatalyst combining the above two properties of TiO2 nanocomposites with different morphologies. TiO2 NPs (5?9?nm nanocrystals form 500?700?nm clusters) have been synthesized from TiCl4 precursor on TiO2 nanotubular arrays (~80?nm diameter and ~550?nm length) synthesized by the sonoelectrochemical anodization method. This TiO2 nanotube?nanoparticle composite photoanode has enabled obtaining of enhanced photocurrent density (2.2?mA?cm?2) as compared with NTs (0.9?mA?cm?2) and NPs (0.65?mA?cm?2) alone.

Bandgap-shifted semiconductor surface and method for making same, and apparatus for using same

Abstract: Titania is a semiconductor and photocatalyst that is also chemically inert. With its bandgap of 3.2 and greater, to activate the photocatalytic property of titania requires light of about 390 nm wavelength, which is in the ultra-violet, where sunlight is very low in intensity. A method and devices are disclosed wherein stress is induced and managed in a thin film of titania in order to shift and lower the bandgap energy into the longer wavelengths that are more abundant in sunlight. Applications of this stress-induced bandgap-shifted titania photocatalytic surface include photoelectrolysis for production of hydrogen gas from water, photovoltaics for production of electricity, and photocatalysis for detoxification and disinfection.

Process for the preparation of titanium dioxide having nanometric dimensions and controlled shape

Abstract: The present invention relates to an industrial applicable process for the preparation of materials with nanometric dimensions and controlled shape, based on titanium dioxide The invention also relates to a process for the preparation of titanium dioxide nanorods with anatase phase composition, which are highly suitable for applications involving photovoltaic cells, particularly Dye Sensitized Solar Cells (DSSC), photoelectrolysis cells and tandem cells for the conversion of solar energy and the production of hydrogen

Photo-Oxidation of Water Using Nanocrystalline Tungsten Oxide under Visible Light

Abstract: The photoelectrolysis of water to yield hydrogen and oxygen using visible light has enormous potential for solar energy harvesting if suitable photoelectrode materials can be developed. Few of the materials with a band gap suitable for visible light activation have the necessary band-edge potentials or photochemical stability to be suitable candidates. Tungsten oxide (𝐸bg 2.8 eV) is a good candidate with absorption up to 𝜆≈440 nm and known photochemical stability. Thin films of tungsten oxide were prepared using an electrolytic route from peroxo-tungsten precursors. The tungsten oxide thin films were characterised by FESEM, Auger electron spectroscopy, and photoelectrochemical methods. The magnitude of the photocurrent response of the films under solar simulated irradiation showed a dependence on precursor used in the film preparation, with a comparatively lower response for samples containing impurities. The photocurrent response spectrum of the tungsten oxide films was more favourable than that recorded for titanium dioxide (TiO2) thin films. The WO3 photocurrent response was of equivalent magnitude but shifted into the visible region of the spectrum, as compared to that of the TiO2.