Marco Altomare

Intrinsic Au Decoration of Growing TiO2 Nanotubes and Formation of a High‐Efficiency Photocatalyst for H2 Production

Electrochemical anodization of low-concentration (0.02-0.2 at% Au) TiAu alloys in a fluoride electrolyte leads to self-organized TiO2 nanotubes that show a controllable, regular in situ decoration with elemental Au nanoclusters of ≈5 nm in diameter. The degree of self-decoration can be adjusted by the Au concentration in the alloy and the anodization time. Such Au particle decorated tubes show a high activity for photocatalytic H2 production from ethanol solutions.

Efficient Photocatalytic H2 Evolution: Controlled Dewetting-Dealloying to Fabricate Site-Selective High-Activity Nanoporous Au Particles on Highly Ordered TiO2 Nanotube Arrays.

Anodic self-organized TiO2 nanostumps are formed and exploited for self-ordering dewetting of Au-Ag sputtered films. This forms ordered particle configurations at the tube top (crown position) or bottom (ground position). By dealloying from a minimal amount of noble metal, porous Au nanoparticles are then formed, which, when in the crown position, allow for a drastically improved photocatalytic H2 production compared with nanoparticles produced by conventional dewetting processes.

Self‐Organized Arrays of Single‐Metal Catalyst Particles in TiO2 Cavities: A Highly Efficient Photocatalytic System

Peas in a pod: A highly aligned Au(np)@TiO2 photocatalyst was formed by self-organizing anodization of a Ti substrate followed by dewetting of a gold thin film. This leads to exactly one Au nanoparticle (np) per TiO2 nanocavity. Such arrays are highly efficient photocatalysts for hydrogen generation from ethanol.

Ta‐Doped TiO2 Nanotubes for Enhanced Solar‐Light Photoelectrochemical Water Splitting

A little dopey: Ta-doped titania (TiO2) nanotube (NT) arrays can be grown by electrochemical anodization onto low-Ta-concentration (0.03-0.4 at % Ta) Ti-Ta alloys. Under optimized conditions (0.1 at % Ta, annealing at 650 °C and 7 μm thickness), Ta-doped TiO2 NT arrays show a significantly enhanced activity in photoelectrochemical water splitting under simulated sunlight conditions (see figure).

Growth of ordered anodic SnO2 nanochannel layers and their use for H2 gas sensing

In the current work, we present a new self-organizing anodization approach of metallic Sn layers to obtain vertically aligned tin oxide nanochannel structures. For this, we use a sulphide-containing electrolyte and a set of optimized anodizing parameters. The resulting high aspect ratio nanochannel morphologies can be converted into crystalline SnO2 by high temperature annealing and show highly promising H2 sensing properties. We show that these anodic layers can operate at relatively low temperatures (∼80 °C), detecting concentrations as low as 9 ppm, and with extremely fast response and recovery times. This excellent gas-sensing performance is ascribed to the advanced structure, characterized by a crack-free, straight and top-open nanochannel geometry.

Use of Anodic TiO2 Nanotube Layers as Mesoporous Scaffolds for Fabricating CH3NH3PbI3 Perovskite‐Based Solid‐State Solar Cells

We optimize the deposition of CH3NH3PbI3 perovskite into mesoporous electrodes consisting of anodic TiO2 nanotube layers. By a simple spin-coating approach, complete filling of the tube scaffolds is obtained, which leads to interdigitated perovskite structures in conformal contact with the TiO2 tube counterparts. Such assemblies can be used as solid-state solar cells in a hole-transporting-material-free configuration, that is, the tube scaffold serves as electron collector and blocking layer, while the perovskite acts as visible-light absorber and hole-transporting material. We show that the complete filling of the tube scaffold with the perovskite is essential to improve the solar cell efficiency.

Molten o-H3PO4: A New Electrolyte for the Anodic Synthesis of Self-Organized Oxide Structures − WO3 Nanochannel Layers and Others

We introduce the use of pure molten ortho-phosphoric acid (o-H3PO4) as an electrolyte for self-organizing electrochemistry. This electrolyte allows for the formation of self-organized oxide architectures (one-dimensional nanotubes, nanochannels, nanopores) on metals such as tungsten that up to now were regarded as very difficult to grow self-ordered anodic oxide structures. In this work, we show particularly the fabrication of thick, vertically aligned tungsten oxide nanochannel layers, with pore diameter of ca. 10 nm and illustrate their potential use in some typical applications.

High-temperature annealing of TiO2 nanotube membranes for efficient dye-sensitized solar cells

We fabricate photo-anodes by transferring anodic TiO2 nanotube membranes in tube-top-down configuration on FTO glass, and use them for constructing frontside illuminated dye-sensitized solar cells. Prior to solar cell construction, the tube-based photo-anodes are crystallized at different temperatures (400–800 °C), and the effects of tube electron transport properties on the photovoltaic performance of the solar cells are investigated. We show that improved solar cell efficiencies (up to ca. 8.0%) can be reached by high-temperature treatment of the tube membranes. Consistent with electron transport time measurements, remarkably enhanced electron mobility is enabled when tube membranes are crystallized at 600 °C.

Free-Standing Membranes to Study the Optical Properties of Anodic TiO2 Nanotube Layers.

In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO2 nanotube layers directly transferred as self-standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thickness varying from 1.8 to 50 μm, and the layers were investigated in their amorphous and crystalline forms. A series of wavelength-dependent light attenuation coefficients are extrapolated and found to match the photocurrent versus irradiation wavelength behavior. A feature specific to anodic nanotubes is that their intrinsic carbon contamination content causes a proportional sub-bandgap response. Overall, the extracted data provide a valuable basis and understanding for the design of photo-electrochemical devices based on TiO2 nanotubes.

Anodic TiO2 nanotube arrays directly grown on quartz glass used in front- and back-side irradiation configuration for photocatalytic H2 generation

In the present work, we explore the front- and back-side performance of a photocatalytic platform consisting of self-organized TiO2 nanotube layers formed by complete anodization of Ti metal films evaporated on quartz slides. The adhesion and light transmission of the tube layers on the quartz surfaces are optimized by a suitable anodization procedure. After their growth, the nanotube arrays were converted into crystalline structures and sputter-coated with co-catalytic Pt nanoparticles. The optically transparent quartz substrates enable the use of the Pt-decorated tube layers for photocatalytic H2 generation under either front- or back-side illumination configurations. The nanotube films on quartz are characterized in view of their physico-chemical properties, including their light transmission features measured using different light sources. The results show that the front-side illumination under optimized factors, i.e., the amount of loaded co-catalyst, yields a maximized photocatalytic performance in terms of H2 generation.