Elpida Piperopoulos

A free-standing aligned-carbon-nanotube/nanocomposite foil as an efficient counter electrode for dye solar cells

A novel free-standing and flexible counter electrode for dye solar cells has been developed by conveniently transferring a vertically aligned carbon nanotube forest onto an oxygen-plasma-treated flexible, free-standing and conductive nanocomposite foil. Vertically aligned carbon nanotubes were first grown onto an aluminium foil by chemical vapour deposition and then transferred to the nanocomposite surface by hot pressing. The most meaningful electrochemical parameters have been quantitatively analyzed by means of electrochemical impedance spectroscopy and cyclic voltammetry in order to elucidate how the implementation of the anisotropic carbon nanotube top layer impacts the ultimate catalytic performances of the plate. Such an engineered counter electrode is able to guarantee a fast and effective reduction of the iodide-based electrolyte as well as to provide a solar conversion efficiency that is comparable with a typical Pt/TCO-coated rigid counter electrode. A photocurrent density higher than 13.36 mA cm−2 along with a solar conversion efficiency of 7.26% have been reported for the dye solar cell mounting a counter-electrode based on vertically aligned carbon nanotubes implanted onto a conductive nanocomposite plate.

Synthesis of SAPO-34/graphite composites for low temperature heat adsorption pumps

Low temperature heat adsorption pumps represent the innovative cooling systems, where cold is generated through adsorption/desorption cycle of water by a suitable adsorbent with good adsorption and high thermal conductive properties. In this work, the hydrothermal synthesis of zeolite SAPO-34 on thermal conductive graphitic supports, aiming at the development of highly performing adsorbent materials, is reported. The synthesis was carried out using as-received and oxidized commercial carbon papers, and graphite plate. Composites were characterized by XRD, SEM and also by a thermogravimetric method, using a Cahn microbalance. The water adsorbing capacity showed typical S-shape trend and the maximum water loading was around 25 wt%, a value close to water adsorption capability of pure SAPO-34. These results are very promising for their application in heat adsorption pumps.

Highly Versatile and Efficient Process for CNT Oxidation in Vapor Phase by Means of Mg(NO3)2‒HNO3‒H2O Ternary Mixture

Nitric acid vapor phase oxidation of carbon nanotubes using Mg(NO3)2‒HNO3‒H2O ternary mixture is proposed as a further development and significant improvement of the method employing the sole azeotropic HNO3 solution. Based on the so-called “salt effect,” the addition of Mg(NO3)2 to HNO3‒H2O solution allows varying the acid vapor concentration within a wide range, even beyond the azeotropic one (>68wt%). Ternary mixture containing 20wt% Mg(NO3)2 and variable amount of liquid HNO3 (30–58wt%) is used for the functionalization process, achieving nitric acid vapor concentrations in the range 25–93wt%. The increase of acid concentration in vapor phase produces a significant augment of the functionalization degree and a linear increase of the concentration of carboxylic acids groups, which can thus be simply tuned.

Influence of the Cobalt Phase on the Highly Efficient Growth of MWNTs

In this work, the influence of the cobalt phase on the growth of carbon nanotubes by the catalytic chemical vapour deposition of CH4 with catalysts containing Co, Mo and Mg is investigated. To this end, the catalytic behaviour of physically mixed CoO/MgO+MgMoO4 and CoMoO4+MgMoO4 is studied. The results obtained show that CoMoO4+MgMoO4 allows for the attainment of the highest CNT yield (2407 wt % against 1296 wt %). Its higher activity is ascribed to the greater formation of active sites that, in light of current assessments, are constituted by metallic cobalt adjacent to Mo2C, and the huge exfoliation of the catalyst, which contributes towards enhancing their exposure.

On the CVD Growth of C Nanotubes Over Fe-Loaded Montmorillonite Catalysts

The synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) of isobutane (i-C4H10) over sodium-exchanged K10-montmorillonite based iron-catalysts is investigated. By studying the influence of iron-addition (5-25 wt%) on the catalyst performances, at 700 °C, an empirical relationship is derived relating the mass of CNTs synthesized with the exposed surface of loaded iron, as resulting from simultaneous change of number, size and dispersion of Fe-nanoparticles available for the growth.

Surface Chemistry and Thermal Stability in Air of Carbon Nanotubes Functionalised via a Novel Eco-Friendly Approach to HNO3 Vapor Oxidation

Some crucial aspects of the functionalisation of carbon nanotubes by nitric acid vapors are investigated, namely selectivity of the process and thermal stability in air of the functionalised materials. Results obtained by varying duration (0.5–5.0 h) of the conventional treatment with vapors at azeotropic HNO3 concentration are compared with those obtained, for fixed duration (2.0 h), by using sub-azeotropic HNO3+H2O+Mg(NO3)2 solution to generate acid vapors with acid concentration in the range 25–93 wt%, as recently proposed by us. A thorough picture is drawn based on evidences of high-resolution transmission electron microscopy, micro Raman spectroscopy, thermo-gravimetry, derivative thermo-gravimetry, and temperature-programmed desorption systematic analyses.

Experimental Methods for the Characterization of Materials for Thermal Energy Storage with Chemical Reactions

The present chapter deals with the experimental characterisation methodologies for TES thermochemical materials with chemical reactions. In particular, thermogravimetric techniques, small-scale reactors configurations and methodologies for the evaluation of thermal energy and power density are discussed. Furthermore, morphological, structural and mechanical characterisations are introduced and applied to typical thermochemical TES materials.

Synthesis of Me Doped Mg(OH)2 Materials for Thermochemical Heat Storage

In order to investigate the influence of metal (Me) doping in Mg(OH)2 synthesis on its thermochemical behavior, Ca2+, Co2+ and Ni2+ ions were inserted in Mg(OH)2 matrix and the resulting materials were investigated for structural, morphological and thermochemical characterization. The densification of the material accompanied by the loss in porosity significantly influenced the hydration process, diminishing the conversion percentage and the kinetics. On the other hand, it increased the volumetric stored/released heat capacity (between 400 and 725 MJ/m3), reaching almost three times the un-doped Mg(OH)2 value.