Francesco Di Benedetto

A Pd/C-CeO2 Anode Catalyst for High-Performance Platinum-Free Anion Exchange Membrane Fuel Cells

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM-FCs). The anion exchange membrane fuel cell (AEM-FC) has long been proposed as a solution as non-Pt metals may be employed. Despite this, few examples of Pt-free AEM-FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt-free AEM-FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt-free AEM-FC that employs a mixed carbon-CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM-FC tests run on dry H2 and pure air show peak power densities of more than 500u2005mWu2009cm(-2) .

Electrochemical milling and faceting: Size reduction and catalytic activation of palladium nanoparticles

Improved performance through milling: A method for enhancing the catalytic activity of supported metal nanoparticles is reported. This method enhances the activity for the ethanol electro-oxidation of a supported palladium catalyst. The much higher catalytic performance is ascribed to the increased electrochemically active surface area as well as the generation of high-index facets at the milled nanoparticle surface.

Compositional zoning in sphalerite crystals

Abstract series of natural sphalerite samples, characterized by an inhomogeneous (zonal) distribution of Fe, Mn, and Cd atoms substituting for Zn, has been investigated by electron probe microanalysis and X-ray element distribution mapping. The cation distributions are markedly inhomogeneous due to the reciprocal effects of the minor elements on their respective solubilities. In particular, zonal partitioning between Fe and Mn and between both cations and Hg was observed in sphalerite, as well as coupled Cu-In and Cu-Fe substitutions. Distinctly different distribution patterns were identified in Mn-free samples with a low Fe-content, as compared to Mn-bearing samples. In the former case, Fe and Cd distribution patterns are very similar, whereas in the latter case, Cd is distributed homogeneously and Mn and Fe patterns are antithetic. The different oscillatory zoning observed in Mn-free samples is attributed to a fast, self-organized solute (Fe, Cd) deposition, although an alternative external origin cannot be ruled out. On the other hand, in the presence of Mn, zoning may be related to an absorption process at the mineral-fluid interface controlled by a competition between Mn and Fe that may explain the observed limited coupled concentration of these elements in sphalerite. The homogeneous distribution of Cd suggests relatively slow crystal growth

First evidence of natural superconductivity covellite

The singular conductive properties of natural covellite were investigated through magnetic AC susceptibility measurements. Two natural hexagonal covellite lamellae coming from Calabona (Italy) and Butte (USA), respectively, were investigated from 30 to 1.5 K. At 1.63(5) K, an abrupt increase of the diamagnetism (Meissner effect) was observed, thus evidencing a transition from a poor conducting to a superconducting state. The transition is independent on small applied DC fields (< 50 Oe), whereas larger values prevent the superconducting state to be attained. These features confirm covellite as a Class I superconductor.nnThis peculiar property of covellite, never observed before on natural materials, can be mainly related to its structural features. The layered framework of covellite, where CuS3 planes are isolated by covalently bonded S2 planes, provides an electron excess, which can be easily involved in the bulk conduction.

Genetic evolution of nanocrystalline Fe oxide and oxyhydroxide assemblages from the Libiola mine (eastern Liguria, Italy) structural and microstructural investigations

The Libiola Fe-Cu-sulphide mine, near Sestri Levante (eastern Liguria), represents one of the most extensively exploited sulphide deposits in Italy. In this area, active Acid Rock Drainage (ARD) processes are evident. The major resulting mineral phases are Fe oxides and oxyhydroxides, occurring in varicoloured crusts on the surface of waste rocks and in unconsolidated muds. In this study, the Fe assemblages of the waste rock were investigated by microchemical (SEM), structural (XRD), microstructural (TEM) and spectroscopic (DRS, IR, μ-Raman) techniques, in order to determine the phase composition, the textural relations among the minerals and their genetic evolution. They are characterized by intimate intergrowths of hematite and goethite with minor quartz and lepidocrocite; in some samples, the presence of very minor schwertmannite was detected. TEM and HR-TEM observations revealed that hematite is present within pseudo-elliptical bodies as pseudo-hexagonal to subrounded nanocrystalline lamellae (from 18.9 to 26.5 nm in diameter), whereas goethite occurs either as parallel intergrowths of acicular crystals (from 10 to 16.3 μm in length) or as sheaf-like assemblages. On the basis of the present data, the studied Fe oxide and oxyhydroxide assemblages are found to represent distinct spatial and temporal stages of a nano-scale evolution process.

Mechanochemical degradation of pentachlorophenol onto birnessite

The existence of a lot of worldwide pentachlorophenol-contaminated sites has induced scientists to concentrate their effort in finding ways to degrade it. Therefore, an effective tool to decompose it from soil mixtures is needed. In this work the efficiency of the phyllomanganate birnessite (KBi) in degrading pentachlorophenol (PCP) through mechanochemical treatments was investigated. To this purpose, a synthesized birnessite and the pollutant were ground together in a high energy mill. The ground KBi-PCP mixtures and the liquid extracts were analyzed to demonstrate that mechanochemical treatments are more efficient in removing PCP than a simple contact between the synthesized birnessite and the pollutant, both in terms of time and extent. The mechanochemically induced PCP degradation mainly occurs through the formation of a surface monodentate inner-sphere complex between the phenolic group of the organic molecules and the structural Mn(IV). This is indicated by the changes induced in birnessite MnO(6) layers as a consequence of the prolonged milling with the pollutant. This mechanism includes the Mn(IV) reduction, the consequent formation of Mn(III) and new vacancies, and free Mn(2+) ions release. The PCP degradation extent is limited by the presence of chloro-substituents on the aromatic ring.

Chemical speciation of Ag in galena by EPR spectroscopy

Abstract Electron paramagnetic resonance (EPR) spectroscopy has been used to study the valence state of silver in “argentiferous” galena samples from the Apuane Alps (Tuscany, Italy) mining district. This method was used to reveal primary metallic silver (Ag0) in galena. Both thermodynamic data and experimental studies suggest that galena and native silver can stably coexist, but have not been reported as a primary (hypogene) assemblage in natural samples. EPR spectroscopy proved to be a suitable tool to solve this problem, because this technique is capable of detecting paramagnetic species down to the ppb level, even in a highly absorbent matrix such as galena. A detailed SEM-EDS investigation could not detect metallic silver (or gold) in galena samples, but did reveal small (few micrometers) inclusions of Ag-bearing phases, in which silver has a formal valence of +1. On the other hand, EPR spectra indicated the presence in galena of pairs and clusters of elemental silver atoms, which may be associated with pairs of metallic gold, or with silver-gold hetero-atomic pairs. Therefore, SEM/EDS and EPR are complementary techniques, revealing the presence of both Ag+ and Ag0. The Ag(Au) metallic species were apparently deposited on the galena surface during its growth from mineralizing fluids. Their scarcity, and the presence of larger amounts of Ag1+ phases, suggest that the assemblage galena-metallic silver was stable only under peculiar physical and chemical conditions. The formation of Ag0 was presumably linked to local and rare chemical fluctuations of the hydrothermal environment, characterized by low activities of S, Sb, Bi (Cu…) and high activity of Ag in the fluids. The occurrence of both homo- and hetero-atomic pairs suggests either different kinetics of pair formation, or possible fluctuations in the composition of the hydrothermal fluids, which alternatively carried Ag or Au species, or both

57Fe Mössbauer and electronic spectroscopy study on a new synthetic hercynite-based pigment

AbstractA new blue hercynite-based pigment,stable at the processing temperatures for the ceramic application,has been synthesized. It isconstituted by corundum and Ti-bearing hercynite. In order to clarify the complex Fe distribution evidenced by Baldi et al. [Proc.CIMTEC 2002(2003)],a 57 Fe Mo¨ssbauer and diffuse reflectance spectroscopy study has been undertaken. Fe was found to be dis-tributed between corundum,as trivalent,and hercynite,both as Fe(II) and Fe(III). Moreover,Fe(II) occupies both tetrahedral andoctahedral sites in the latter mineral,according to a temperature dependent disorder. UV–VIS investigation revealed the presence ofa broad band in the blue region,the shape and position of which was found to be due to an intervalence charge transfer mechanismbetween Fe(II) and Ti(IV) in two edge-sharing octahedra of hercynite.# 2003 Elsevier Ltd. All rights reserved. Keywords:Al 2 O 3 ; Colour; Pigment; Spectroscopy; Spinels 1. IntroductionCeramic pigments are white or coloured crystallinematerials with high thermal stability and high chemicalresistance. These properties are strategic for their use inhigh temperature treatments. In recent years the devel-opment of new ceramic materials has fostered theresearch of pigments stable at application temperaturesover 1200 C. The crystalline coloured substances thatremain unaltered in such conditions belong to a restric-ted number of structures: zirconium silicate ZrSiO

Mechanochemical transformation of an organic ligand on mineral surfaces: the efficiency of birnessite in catechol degradation.

The aim of this work is to investigate the efficiency of the phyllomanganate birnessite in degrading catechol after mechanochemical treatments. A synthesized birnessite and the organic molecule were grounded together in a high energy mill and the xenobiotic-mineral surface reactions induced by the grinding treatment have been investigated by means of X-ray powder diffraction, X-ray fluorescence, thermal analysis and spectroscopic techniques as well as high-performance liquid chromatography and voltammetric techniques. If compared to the simple contact between the birnessite and the organic molecule, mechanochemical treatments have revealed to be highly efficient in degrading catechol molecules, in terms both of time and extent. Due to the two phenolic groups of catechol and the small steric hindrance of the molecule, the extent of the mechanochemically induced degradation of catechol onto birnessite surfaces is quite high. The degradation mechanism mainly occurs via a redox reaction. It implies the formation of a surface bidentate inner-sphere complex between the phenolic group of the organic molecules and the Mn(IV) from the birnessite structure. Structural changes occur on the MnO(6) layers of birnessite as due to the mechanically induced surface reactions: reduction of Mn(IV), consequent formation of Mn(III) and new vacancies, and free Mn(2+) ions production.

EPR and magnetic investigations on sulphides and sulphosalts

Magnetometric studies of sulphide and sulphosalt minerals were carried out using electron paramagnetic resonance (EPR) and a superconducting quantum interference device (SQUID). These have proved to be powerful tools to investigate not only the valence states of transition elements (TE) cations but also the site symmetries and magnetic interactions between neighbouring atoms. While only few investigations are found in literature concerning sulphide minerals in recent years, advanced resonance techniques, such as electron spin echoes (ESE) and high-frequency EPR (HF 2 EPR), allow us to supplement and extend the information that can be obtained with standard techniques. Sphalerite derivative structures, such as stannite and tetrahedrite, were object of a systematic and advanced EPR and SQUID investigation. Synthetic analogues with simple chemical composition are here used as reference materials for the interpretation of the spectra refined by computer simulation. Spectroscopic investigations on these materials allow us to establish the different nature of “free” electrons delocalized with respect to the usual unpaired electrons of Cu(II), while preliminary studies on the ZnS-archetype, doped with TE, prove to be very useful in refining the site symmetries of cations in the structure.