N. Casañ-Pastor

Hybrid organic-inorganic nanocomposite materials for application in solid state electrochemical supercapacitors

Integration into a conducting polymer matrix to form a hybrid material is an effective way to harness the electrochemical activity of nanosized oxide clusters. By anchoring them into polyaniline, the reversible redox chemistry of the otherwise soluble polyoxometalate clusters can be combined with that of the conducting polymer and be put to work in energy storage applications. We present here preliminary results that show how the resulting hybrid polymer displays the combined activity of its organic and inorganic components to store and release charge in a solid state electrochemical capacitor device.

Polyoxometalates: from inorganic chemistry to materials science.

Polyoxometalates have been traditionally the subject of study of molecular inorganic chemistry. Yet, these polynuclear molecules, reminiscent of oxide clusters, present a wide range of structures and with them ideal frameworks for the deployment of a plethora of useful magnetic, electroionic, catalytic, bioactive and photochemical properties. With this in mind, a new trend towards the application of these remarkable species in materials science is beginning to develop. In this review we analyze this trend and discuss two main lines of thought for the application of polyoxometalates as materials. On the one hand, there is their use as clusters with inherently useful properties on themselves, a line which has produced fundamental studies of their magnetic, electronic or photoelectrochemical properties and has shown these clusters as models for quantum-sized oxides. On the other hand, the encapsulation or integration of polyoxometalates into organic, polymeric or inorganic matrices or substrates opens a whole new field within the area of hybrid materials for harnessing the multifunctional properties of these versatile species in a wide variety of applications, ranging from catalysis to energy storage to biomedicine.

Detrimental Effect of Inert Atmospheres on Hybrid Solar Cells Based on Semiconductor Oxides

We report the improvement observed in J sc , V oc , and current-voltage (1-V) curves when hybrid solar cells (HSCs) are transferred from inert conditions to ambient atmosphere. The effect is observed regardless of the semiconductor oxide applied and has been attributed to the reversible incorporation of oxygen from the atmosphere into the semiconductor oxide surface during illumination. The HSCs were prepared as bilayers of thin-film semiconductor oxides (TiO 2 , Nb 2 O 5 , and ZnO) made by the sol-gel technique and the polymer poly[(2-methoxy-5-ethylhexyloxy)-l,4-phenylenevinylene] (MEH-PPV), applying a final device configuration of the type indium tin oxide/oxide thin film /MEH-PPV/Ag. The photovoltaic response was studied in terms of inert atmosphere by recording the initial values of open-circuit voltage (V oc ) and current density (J sc ). Solar decay curves, I-V curves, the effect of filter and resting time, as well as photophysical analyses were also carried out for each type of device.

Oxygen excess and superconductivity at 45 K in La2CaCu2O6+y

Abstract Preparation of single-phase stoichiometric La 2 CaCu 2 O 6+ y from oxide precursors is reported along with high-resolution neutron powder diffraction studies. To date this is the only route that allows the stoichiometric phase to be obtained. An air-heated sample having y =0.0378(8) displays a transition onset at 45 K to diamagnetic susceptibility. Nevertheless, the maximum amount of superconducting phase inferred from these flux exclusion experiments is only 1% in volume. It is also found that the diamagnetic signal is not substantially modified by changing the annealing atmosphere at normal pressures. Neutron diffraction data show a high atomic ordering of La and Ca ions with a strong preference (75%) of Ca ions for sites eight-fold coordinated located between the Cu-O 2 planes. The other 25% is occupied by La ions, around which the excess oxygen is located with partial occupancies, yielding a higher coordination number for some of these La ions. Comparison of this structure with that of the nonsuperconducting oxide La 1.9 Ca 1.1 Cu 2 O 6+ y , suggests that the observed small superconductivity islands are related to clustered oxygen excess intercalated between the two Cu-O 2 planes, along with the La ions. The small overall concentration of defects observed here, and thus the small number of holes, is responsible for the absence of bulk superconductivity in La 2 CaCu 2 O 6+ y .

Chemical polymerization of polyaniline and polypyrrole by phosphomolybdic acid : In situ formation of hybrid organic-inorganic materials

The oxidative polymerization of aniline or pyrrole by phosphomolybdic acid (H 3 PMo 12 O 40 ) is described. These reactions take place in the absence of other anions and result in the incorporation of the photoactive and electroactive PMo 12 O 40 3- anion into the lattice of the polymer. The resulting hybrid materials present the good conductivity and polymeric nature of the matrix plus the added electroactivity of the inorganic cluster, which is anchored in the polymer and not exchanged upon reduction. The hybrids can work as electrodes harnessing the electrochemical properties of the polyoxometalic clusters.

Electrochemically induced reversible solid state transformations: electrosynthesis of Ag2Cu2O4 by room temperature oxidation of Ag2Cu2O3

Electrochemical oxidation at room temperature of a slurry of Ag2Cu2O3 yields a new silver copper oxide, formulated as Ag2Cu2O4, with one more atom of oxygen per unit formula, that can in turn revert to the original precursor. The resulting oxide presents a different electronic and crystal structure from its precursor, as shown by XPS, X-ray and electron diffraction. This phase transformation involves a radical structural change from a 3D to a 2D network, as well as electronic changes involving silver and oxygen. The potential of electrochemical techniques to induce crystal-chemical solid state transformations is analyzed.

Synthesis deintercalation and transport properties of a mixed-valence derivative of the layered oxide HLaNb2O7

We have synthesized mixed-valence derivatives of the layered oxide HLa Nb2O7, structurally related to perovskite, by chemical reduction, either at room temperature or at 650 °C. The thermal behavior of this compound, its structure and change in transport properties upon high temperature doping are discussed. High temperature reduction turns the white insulating precursor into a mixed-valence blue bronze with a layered structure and semiconducting-like properties.

Electrochemical oxidation of lanthanum cuprates. Superconductivity versus thermal treatment in La2CuO4+δ

Abstract Room-temperature electrochemical oxidation of La 2 CuO 4 at the limiting value of 0.15 electrons per formula unit yields bulk superconducting materials with T c values that depend on the applied potentials and the drying temperature. Superconducting fractions and structural parameters are also strongly dependent on moderate thermal treatments following the synthesis. We propose a reorganization of the charge carriers with temperature, involving charge transfer between Cu and intercalated oxygen atoms, to explain the analytical data obtained for various samples with different thermal treatments. Other cuprates also show the ability to intercalate oxygen. Thus, electrochemical oxidation of La 2− x Sr x CaCu 2 O 6−δ yields the oxygen stoichiometric phase that, although not superconducting, presents magnetic properties different from its precursor without a notable change in its structure.

Structural study of electrochemically-synthesized Ag2Cu2O4. A novel oxide sensitive to irradiation

Abstract The structure of Ag 2 Cu 2 O 4 synthesized by electrochemical oxidation of its precursor Ag 2 Cu 2 O 3 is studied under a new perspective. Irradiation of the oxide with X-ray beam transforms the electronic structure of the phase by redistributing the internal charge within the material. The refined structure shows several possibilities all with metals in the same arrangement, but with oxygen atoms distributed in a rather disordered way. This is typical of ionic conductors.

Synthesis structure and superconductivity in all-perovskite-layered titanium cuprates☆

A study on the reaction pathways, the synthesis, and the range of stability of complex perovskites in the system Ln-(Sr/Ba)-Cu-Ti is reported. Several possibilities for the Cu: Ti stoichiometry were explored with the aim of isolating potentially superconducting layered phases. A bulk superconducting phase of the formula YSr{sub 2}Cu{sub 2.7}Ti{sub 0.3}O{sub 8-{delta}} with a T{sub c} of 26 K was isolated and a whole family of layered oxides of the formula Ln{sub 2}Ba{sub 2}Cu{sub 2}Ti{sub 2}O{sub 11-{delta}} with a T{sub c} of 26 K was isolated and a whole family of layered oxides of the formula Ln{sub 2}Ba{sub 2}Cu{sub 2}Ti{sub 2}O{sub 11-{delta}} was characterized. The authors have determined the limits of this family which extends form Ln = La to Tb. The studies reported include X-ray and electron diffraction, and TGA and magnetic susceptibility measurements. Structural and magnetic correlations for these oxides are analyzed.