Francesco Cardellini

Comparison of high surface Pt/C catalysts by cyclic voltammetry

A detailed procedure for comparing high surface Pt/C catalysts was pointed out. Platinum dispersed carbon was prepared from carbonaceous material and chloroplatinic acid solution using sodium formiate. The real platinum metal surface area was evaluated by cyclic voltammetry on a thin porous coated disk electrode. The performance of catalysts prepared in our laboratory were similar to those of a well-known commercial one. The results show that electrochemical active surface (EAS) measurement is strongly influenced by the gas diffusion electrode (GDE) preparative method. It is only by means of a well-defined preparative procedure and data analysis that it is possible to use this technique to compare different carbon supported platinum catalysts.

Synthesis and Characterization of Amorphous Hydrated FePO4 and Its Electrode Performance in Lithium Batteries

Amorphous iron(III) phosphate was synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O and NH 4 H 2 PO 4 , using hydrogen peroxide as the oxidizing agent. The material was characterized by chemical analysis thermogravimetrical analysis, differential thermoanalysis, X-ray powder diffraction, and scanning electron microscopy. The material was tested as a cathode in nonaqueous lithium cells Galvanostatic intermittent titration technique was used to follow the lithium intercalation process The effect of firing on the specific capacity was also tested. The material lired at 400°C showed the best electrochemical performance, delivering about 0.108 Ah g -1 when cycled at C/10 rate. The capacity fade upon cycling was found as low as 0.075% per cycle.

A novel route to prepare stable Pt-Ru/C electrocatalysts for polymer electrolyte fuel cell

A new method for preparing high surface Pt–Ru/C catalysts at low temperature is described. Pt–Ru on carbon was prepared from carbonaceous material, Pt(NH3)4Cl2 and RuNO(NO3)x(OH)y with borohydride as a reducing agent. Simultaneous reduction of both metals was provided by means of heat treatment. Small and homogeneously dispersed catalyst particles were obtained. XRD and electrochemical measurements show that the performance of the catalyst prepared was similar to that of commercial E-Tek samples, but with increased stability.

Experimental and theoretical investigation of the order-disorder transformation in Ni3Al

The crystalline disordered phase obtained by mechanical alloying of elemental 75 at. % Ni and 25 at. % Al powders has been investigated. The stability of this phase with respect to the thermal reordering process leading to the L1 2 structure has been analyzed by means of x-ray diffractometry, scanning electron microscopy, and differential scanning calorimetry. Atomistic simulations on an Ni 3 Al model, reproduced via molecular dynamics using a many-body potential, have been used to interpret experimental data. The ordering transformation takes place in an extended range of temperature (from 320 to 600 °C) and occurs simultaneously with the release of internal strain. Numerical simulations performed under different conditions show that the activation energy of the Ni-vacancy migration mechanism responsible for the ordering process depends on the local state of strain, thus suggesting an explanation for the considerable lowering of this energy in samples obtained by ball milling.

Optical and electrochemical properties of cerium-zirconium mixed oxide thin films deposited by sol-gel and r.f. sputtering

Films of Ce‐Zr mixed oxide were produced by sol‐gel and r.f. sputtering. These films can be used as ‘passive’ counter-electrodes in electrochromic smart windows because they retain their full transparency in both the oxidised and reduced state. Li intercalation was accomplished electrochemically using a liquid electrolyte. Electrochemical behaviour of the samples was found to be dependent on the heat treatment (sol‐gel deposited film) and crystallite orientation (sputter deposited films). XRD analysis on sputter deposited films showed that the films are crystalline and grow following the orientation of the underlying tin doped indium oxide (ITO) film. Films of Ce‐Zr mixed oxide lacking in (111) crystallite orientation show continuous evolution of the voltammograms and reach a maximum value for the cycled charge only after a large number of cycles. The lithium diAusion coeAcient, calculated from GITT measurements, is in the range 10 ˇ12 ‐10 ˇ14 cm 2 s ˇ1 for sputter deposited films and becomes as low as 10 ˇ15 cm 2 s ˇ1 for sol‐gel deposited films. Optical constants of the thin films were calculated from reflectance and transmittance spectra. Refractive index values are in the range of 2.15‐2.30 at l=633 mn depending on the deposition method. A sharp absorption edge at about 320 nm is seen in accordance with CeO2 optical properties. # 1999 Elsevier Science Ltd. All rights reserved.

Correction for radon distribution in solid/liquid and air phases in gamma-ray spectrometry.

The effect of radon diffusion and distribution between a (226)Ra matrix and the top air gap inside sample containers for gamma-ray spectrometry was studied. Containers filled at almost 100% or just 70% of total capacity yielded correction factors of about 7% and 20% respectively. Applying these correction factors allowed activity values calculated from (226)Ra or radon decay products to agree within 2%.

Influence of Morphology and Structure of Cu/In Alloys on the Properties of CuInSe2

Thin CuInSe2 films were prepared by selenization of sputtered metal precursors. The surface morphology, phase composition and adhesion at the Mo/glass substrate of the ternary compound have been correlated to the structure of the precursor. Single phase, homogeneous, small grained (1 µm) CuInSe2 arises from precursors showing stable phases (Cu11In9 and In). An ordered vacancy compound (CuIn3Se5) is likely present in In-rich (In>27 at.%) films. Precursors with a high content of the metastable CuIn2 phase show a very poor adhesion to the substrate.

Synthesis of a bicontinuous electrically conductive nanocomposite via in-situ formation of RuO2 nanoparticles

The synthesis of a nanocomposite material obtained via the in-situ formation of ruthenium oxide nanoparticles on and between commercial lithium manganese oxide particles is reported. Electrochemical tests have shown that the synthesized nanocomposite material is characterized by a bicontinuous morphology in which the solid phase and pore phase are continuous, interpenetrating and exhibit high electronic conductivity.

Mechanical alloying of immiscible elements : experimental results on Ag-Cu and Co-Cu

Abstract Equimolar solid solutions of Ag[sbnd]Cu and Co[sbnd]Cu were prepared by mechanical milling of the elements. The structure and the thermodynamic properties of the resulting phases were analysed by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Large mixing enthalpies (ΔH = 6–8kJg-atom−1 and ΔH = 4–8kJg-atom−1 for Ag-Cu and Co-Cu respectively) were measured in the alloyed phases. It is clear that the solid solution forms through a process of grain refinement down to the nanometre scale and is assisted by an atomic-scale dissolution. The possible role played by coherent interfaces in substantially increasing the energy of the solid solutions is discussed.

Nanocrystalline Al‒Fe alloys synthesized by high-energy ball milling

Abstract This study describes the effect of ball milling and heat treatment on the phases synthesized in a Spex mill starting from mixtures of Al and Fe powders containing 71, 75, 80 and 90 at.% A1. In the 71 and 75 at.% Al mixtures we observed the formation of the Al5Fe2 phase. At the 80 at.% Al concentration we observed the formation of an Al-rich ultrafine phase with a coherent domain size of the order of 1 nm. At the 90 at.% Al concentration, no new phase is observed to nucleate for milling times up to 50 hs. The thermal behaviour of the samples depends on the time of the milling. At all compositions, we observed the nucleation of the metastable A16Fe compound at about 320°C on heating of samples milled for short times (10 h or less) and the formation of the equilibrium phase(s) upon heating to 600°C.