Gianluigi Marra

Photoanodes Based on Nanostructured WO3 for Water Splitting

Anodically grown WO(3) photoelectrodes prepared in an N-methylformamide (NMF) electrolyte have been investigated with the aim of exploring the effects induced by anodization time and water concentration in the electrochemical bath on the properties of the resulting photoanodes. An n-type WO(3) semiconductor is one of the most promising photoanodes for hydrogen production from water splitting and the electrochemical anodization of tungsten allows very good photoelectrodes, which are characterized by a low charge-transfer resistance and an increased spectral response in the visible region, to be obtained. These photoanodes were investigated by a combination of steady state and transient photoelectrochemical techniques and a correlation between photocurrent produced, morphology, and charge transport has been evaluated.

Solvent-free phenyl-C61-butyric acid methyl ester (PCBM) from clathrates: insights for organic photovoltaics from crystal structures and molecular dynamics

The first solvent-free crystal structure of PCBM, an organic semiconductor widely used in solvent-free nanocrystalline films in plastic solar cells, is reported and its relevance to structure-property relationships discussed. The PCBM structure, obtained from o-dichlorobenzene solvates by solvent abstraction, was solved using powder diffraction, demonstrating this possibility for functionalized fullerenes.

Hybrid organic–inorganic H2-evolving photocathodes: understanding the route towards high performance organic photoelectrochemical water splitting

A promising, yet challenging, route towards renewable production of hydrogen is the direct conversion of solar energy at a simple and low cost semiconductor/water junction. Despite the theoretical simplicity of such a photoelectrochemical device, different limitations among candidate semiconductor materials have hindered its development. After many decades of research on inorganic semiconductors, a conclusive solution still appears out of reach. Here, we report an efficient hybrid organic–inorganic H2 evolving photocathode, consisting of a donor/acceptor blend sandwiched between charge-selective layers and a thin electrocatalyst layer. The role and stability of the different interfaces are investigated, and the conductive polymer is proven to be an efficient material for a semiconductor/liquid PEC junction. The best performing electrodes show high performances with a photocurrent of 3 mA cm−2 at 0 V vs. RHE, optimal process stability with 100% faradaic efficiency during electrodes lifetime, excellent energetics with +0.67 V vs. RHE onset potential, promising operational activity of several hours and by-design compatibility for implementation in a tandem architecture. This work demonstrates organic semiconductors as a radically new option for efficient direct conversion of solar energy into fuels, and points out the route towards high performance organic photoelectrochemical water splitting.

Quasi-1D hyperbranched WO3 nanostructures for low-voltage photoelectrochemical water splitting

Arrays of hyperbranched high aspect ratio mesostructures are grown by pulsed laser deposition through a self-assembly process from the gas phase. These hierarchical arrays are successfully used as photoanodes for the photoelectrochemical splitting of water, exhibiting an onset potential as low as 0.4 V vs. RHE and saturation current densities up to 1.85 mA cm−2 at 0.8 V vs. RHE. While the latter is similar to the state of the art values for WO3 nanostructured photoanodes, both the onset and saturation voltages are significantly lower than any other reported values. This peculiar behavior is attributed to the hyperbranched structure and to its excellent optical and electronic properties.

Loading silica with metals (palladium or platinum) under mild conditions by using well-defined molecular precursors

The loading of pre-treated amorphous silica with platinum or palladium was carried out by using the molecular precursors Pt2(micro-Cl)2Cl2(CO)2, or Pd2(micro-Cl)2Cl2(CO)2, respectively, which contain the required amount of coordinated CO to carry out the formation of the metal particles upon contact with moisture. The reactivity of the well-soluble mononuclear platinum complex cis-PtCl2(CO)2 with stoichiometric amounts of water was investigated either under N2 or CO. The metal nanoparticles produced on the silica matrix have been characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The catalytic performance of the silica-supported metals thus produced was evaluated in the hydrogenation of cyclohexene.

Pre-burning Characterization of Nanosized Aluminum in Condensed Energetic Systems

Abstract Nano-sized aluminum (nAl) particles have several features that make them interesting for energetic applications. Compared to micron-sized aluminum (μAl) higher reactivity, lower ignition temperature and condensed combustion products of reduced size can be achieved. This work focuses on the pre-burning characterization of nAl. In the analysis, different features of various powders (passivated by air or organic compounds, and eventually coated by hydrocarbons and fluorohydrocarbons) are investigated focusing on the application in energetic systems. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (SSA) measurement, and volumetric techniques are considered for an extensive characterization of the powder morphology (particle size, shape, and texture), structure, and composition (active metal content). The reactivity of nAl is investigated at low- and high-heating rates. The behavior of powder suspensions is analyzed by a plate–plate rheometer considering hydroxyl-terminated polybutadiene (HTPB) as the suspending medium. The effects of the nAl passivation/coating layer on the viscosity of HTPB-based slurries are discussed. This information is crucial for an effective evaluation of the nanomaterial dispersion in the HTPB matrix and for the identification of possible limitations in the propellant/fuel manufacturing process. The presented results enable a comprehensive understanding of the relationships between nanosized additives morphology/structure, oxidative reactivity, and propellant/fuel rheological behavior.

Molding of syndiotactic polystyrene under its melting temperature

Syndiotactic polystyrene (SPS), a thermoplastic polymer that exhibits a high T m in some crystalline forms, can be conveniently processed by a cold-compaction technique. Processing temperatures in the range of 150-210°C, well below the T m , v gives rise to physicomechanical properties comparable and even better than those obtained by thermal compression or injection molding. The optimum treatment temperature seems to fall around 175°C. X-ray diffraction analysis, thermal analysis, and density measurements suggest that such behavior is connected to phase transitions of SPS and favored by the presence of styrene included in the crystalline fraction.