Claudio a Mari

Ultrathin Spinel LiMn2O4 Nanowires as High Power Cathode Materials for Li-Ion Batteries

Ultrathin LiMn(2)O(4) nanowires with cubic spinel structure were synthesized by using a solvothermal reaction to produce α-MnO(2) nanowire followed by solid-state lithiation. LiMn(2)O(4) nanowires have diameters less than 10 nm and lengths of several micrometers. Galvanostatic battery testing showed that LiMn(2)O(4) nanowires deliver 100 and 78 mAh/g at very high rate (60C and 150C, respectively) in a larger potential window with very good capacity retention and outstanding structural stability. Such performances are due to both the favorable morphology and the high crystallinity of nanowires.

Investigations on the ion transport mechanism in conducting polymer films

The change in the electrical properties were investigated as a function of relative humidity by several techniques (among them the electrochemical impedance) for different ion-conducting polymers, sprayed as films on interdigitated gold electrodes. It was found that the equations valid for electrolytic solutions fit the experimental data. In particular, the Onsager equation, applied to the relevant parameters of the polymeric films, describes the change in the film resistance as a function of relative humidity satisfactorily.

Macroporous WO3 Thin Films Active in NH3 Sensing: Role of the Hosted Cr Isolated Centers and Pt Nanoclusters

Macroporous WO(3) films with inverted opal structure were synthesized by one-step procedure, which involves the self-assembly of the spherical templating agents and the simultaneous sol-gel condensation of the semiconductor alkoxide precursor. Transition metal doping, aimed to enhance the WO(3) electrical response, was carried out by including Cr(III) and Pt(IV) centers in the oxide matrix. It turned out that Cr remains as homogeneously dispersed Cr(III) centers inside the WO(3) host, while Pt undergoes reduction and aggregation to form nanoclusters located at the oxide surface. Upon interaction with NH(3), the electrical conductivity of transition metal doped-WO(3) increases, especially in the presence of Pt dopant, resulting in outstanding sensing properties (S = 110 ± 15 at T = 225 °C and [NH(3)] = 74 ppm). A mechanism was suggested to explain the excellent electrical response of Pt-doped films with respect to the Cr-doped ones. This associates the easy chemisorption of ammonia on the WO(3) nanocrystals, promoted by the inverted opal structure, with the catalytic action exerted by the surface Pt nanoclusters on the N-H bond dissociation. The overall results indicate that in Pt-doped WO(3) films the effects of the macroporosity positively combine with the electrical sensitization promoted by the metal nanoclusters, thus providing very lightweight materials which display high functionality even at relatively low temperatures. We expect that this synergistic effect can be exploited to realize other functional hierarchical metal oxide structures to be used as gas sensors or catalysts.

Assessment of Water-Soluble π-Extended Squaraines as One- and Two-Photon Singlet Oxygen Photosensitizers: Design, Synthesis, and Characterization

Singlet oxygen sensitization by organic molecules is a topic of major interest in the development of both efficient photodynamic therapy (PDT) and aerobic oxidations under complete green chemistry conditions. We report on the design, synthesis, biology, and complete spectroscopic characterization (vis-NIR linear and two-photon absorption spectroscopy, singlet oxygen generation efficiencies for both one- and two-photon excitation, electrochemistry, intrinsic dark toxicity, cellular uptake, and subcellular localization) of three classes of innovative singlet oxygen sensitizers pertaining to the family of symmetric squaraine derivatives originating from pi-excessive heterocycles. The main advantage of pi-extended squaraine photosensitizers over the large number of other known photosensitizers is their exceedingly strong two-photon absorption enabling, together with sizable singlet oxygen sensitization capabilities, for their use at the clinical application relevant wavelength of 806 nm. We finally show encouraging results about the dark toxicity and cellular uptake capabilities of water-soluble squaraine photosensitizers, opening the way for clinical small animal PDT trials.

Layered Na0.71CoO2: a powerful candidate for viable and high performance Na-batteries

The present study reports on the synthesis and the electrochemical behavior of Na(0.71)CoO(2), a promising candidate as cathode for Na-based batteries. The material was obtained in two different morphologies by a double-step route, which is cheap and easy to scale up: the hydrothermal synthesis to produce Co(3)O(4) with tailored and nanometric morphology, followed by the solid-state reaction with NaOH, or alternatively with Na(2)CO(3), to promote Na intercalation. Both products are highly crystalline and have the P2-Na(0.71)CoO(2) crystal phase, but differ in the respective morphologies. The material obtained from Na(2)CO(3) have a narrow particle length (edge to edge) distribution and 2D platelet morphology, while those from NaOH exhibit large microcrystals, irregular in shape, with broad particle length distribution and undefined exposed surfaces. Electrochemical analysis shows the good performances of these materials as a positive electrode for Na-ion half cells. In particular, Na(0.71)CoO(2) thin microplatelets exhibit the best behavior with stable discharge specific capacities of 120 and 80 mAh g(-1) at 5 and 40 mA g(-1), respectively, in the range 2.0-3.9 V vs. Na(+)/Na. These outstanding properties make this material a promising candidate to construct viable and high-performance Na-based batteries.

Preparation, structure and electrical properties of thick ruthenium dioxide films

Abstract Results of measurements of x-ray diffraction, electron scanning microscopy and electrical conductivity of thick, polycrystalline RuO 2 films obtained by decomposing ruthenium trichloride are presented and discussed. The influence of the preparation procedure, process temperature, chlorine content and nature of the substrate on electrical and structural properties is also considered.

Shape-Controlled TiO2 Nanocrystals for Na-Ion Battery Electrodes: The Role of Different Exposed Crystal Facets on the Electrochemical Properties

Rechargeable sodium-ion batteries are becoming a viable alternative to lithium-based technology in energy storage strategies, due to the wide abundance of sodium raw material. In the past decade, this has generated a boom of research interest in such systems. Notwithstanding the large number of research papers concerning sodium-ion battery electrodes, the development of a low-cost, well-performing anode material remains the largest obstacle to overcome. Although the well-known anatase, one of the allotropic forms of natural TiO2, was recently proposed for such applications, the material generally suffers from reduced cyclability and limited power, due to kinetic drawbacks and to its poor charge transport properties. A systematic approach in the morphological tuning of the anatase nanocrystals is needed, to optimize its structural features toward the electrochemical properties and to promote the material interaction with the conductive network and the electrolyte. Aiming to face with these issues, we were able to obtain a fine tuning of the nanoparticle morphology and to expose the most favorable nanocrystal facets to the electrolyte and to the conductive wrapping agent (graphene), thus overcoming the intrinsic limits of anatase transport properties. The result is a TiO2-based composite electrode able to deliver an outstandingly stability over cycles (150 mA h g-1 for more than 600 cycles in the 1.5-0.1 V potential range) never achieved with such a low content of carbonaceous substrate (5%). Moreover, it has been demonstrated for the first time than these outstanding performances are not simply related to the overall surface area of the different morphologies but have to be directly related to the peculiar surface characteristics of the crystals.

Alkaline glucose oxidation on nanostructured gold electrodes

The electrocatalytic properties of nanostructured gold electrodes for glucose electro-oxidation in KOH were investigated by cyclic voltammetry and compared with a commercially available polycrystalline gold electrode. These electrodes were prepared by depositing gold nanoparticles from a sol onto different carbonaceous conductive supports: glassy carbon, carbon cloth and graphite paper. The gold sol was prepared reducing an aqueous solution of tetrachloroauric acid with sodium borohydride. In order to improve gold nanoparticle adhesion, the substrate surfaces were treated with warm concentrated nitric acid. Gold on treated carbon cloth turned out to be a very promising anode for glucose electro-oxidation. In order to better understand the glucose oxidation its pH dependence as well as sorbitol (the glucose reduction product) electroxidation were investigated.

Panchromatic Cross-Substituted Squaraines for Dye-Sensitized Solar Cell Applications

Keywords: light harvesting ; photochromism ; sensitizers ; solar cells ; squaraines ; Organic Sensitizers ; Highly Efficient Reference EPFL-ARTICLE-159583doi:10.1002/cssc.200900077View record in Web of Science Record created on 2010-11-30, modified on 2017-05-12

Surface reactivity of nanostructured tin oxide and Pt-doped tin oxide as studied by EPR and XPS spectroscopies

Abstract Nanostructured (3–6 nm) thin films (80 nm) of SnO 2 and Pt-doped SnO 2 were obtained by a new sol–gel route using tetra( tert -butoxy)tin(IV) and bis(acetylacetonato)platinum(II) as precursors. EPR and XPS investigations, performed on thin films after interaction with CO, demonstrated that singly ionized oxygen vacancies (V o ) fully transferred their electrons to the noble metal and reduced Pt(IV) to Pt(II). Contact with air at room temperature led to the reduction of O 2 to O 2 − , therefore, re-oxidizing metal centers. The reaction mechanism concords with the high electrical sensitivity of this material.