RESUMO Neste trabalho são aplicados corantes extraídos de plantas da Floresta Amazônica como sensibilizadores em células solares sensibilizadas por corantes. As plantas selecionadas foram Euterpe oleracea, Arrabidaea chica, Bixa orellana, Genipa americana e Myrcia sylvatica e os corantes foram coletados de frutos, folhas, sementes, polpa e sementes e do caule, respectivamente. Os estudos de caracterização através da espectroscopia UV-vis possibilitaram conhecer os espectros de absorção para cada corante e a técnica de difração de raios X permitiu a caracterização estrutural da camada semicondutora nanoestruturada. As células solares foram caracterizadas quanto a seus parâmetros de eficiência (Voc, Jsc, FF e ? (%)), obtidas das curvas de corrente vs potencial. Tais parâmetros se mostraram modestos, apresentando valores de Voc sobre os 0,334 volts e Jsc de 0,452 mA/cm2 para célula fotossensibilizada com o corante extraído da Genipa americana. Dessa forma foi possível verificar o potencial fotoeletroquímico dos corantes extraídos de plantas da Floresta Amazônica.

ABSTRACT In this work, plant dyes extracted from Amazon Forest are applied as a sensitizer in Dye-Sensitized Solar Cells. The selected plants were Euterpe oleracea, Arrabidaea chica, Bixa orellana, Genipa Americana, and Myrcia sylvatica, and the dyes were collected from fruits, leaves, seeds, pulp and seeds and stalk scrapings respectively. Characterization studies by the UV-vis spectroscopy made it possible to know the absorption spectra of each plant dye, and the X-ray diffraction technique allows the structural characterization of the nanostructured semiconductor layer. The solar cells were characterized according to their efficiency parameters (Voc, Jsc, FF and ? (%)), obtained from the current vs voltage curves. Such parameters proved to be modest, presenting Voc and Jsc values over 0.334 volts and 0.452 mA/cm2 for a photosensitized cell with the dyes extracted from Genipa americana. In this way, it was possible to verify the photoelectrochemical potential of the dyes extracted from plants of the Amazon Forest.

This work reports the synthesization of nanoparticles cobalt oxide (Co3O4) with no secondary phase by a modified sol-gel method and its structural morphological and electrochemical characterizations. FTIR, XRD and Raman analysis showed the formation of spinel cobalt oxide with no secondary phase. TEM images revealed that an undefined morphology with average crystallite size estimated by Scherrer's equation was found to be 30 nm. Experiments of cyclic voltametric, galvanostatic charge-discharge and impedance spectroscopy were evaluated at 1 mol L-1 KOH and revealed an intrinsic pseudocapacitance. The studies of complex capacitance and complex power revealed the resistive and capacitive characteristics with a specific capacitance of 120 F g-1.

ABSTRACT Direct Alcohol Fuel Cells (DAFC’s) are an alternative to fuel cell systems and when is used alkaline medium this has an increase performance. The alkaline direct alcohol fuel cells (ADAFC's) have some advantages such as low-emission, high energy efficiency, improved oxidation kinetics, low crossover and in addition there is a broad range of materials that can be used as catalysts. The ethylene glycol (EG) has received attention in recent decades as an alternative fuel for ADAFC, but like others alcohols must be completed oxidized to generate full power energy. In this study we analyzed ternary PtRhNi/C electrocatalysts with different compositions, synthesized by alcohol reduction method, and compared to Pt/C ETEK. The active area, catalytic activity and stability of catalysts for ethylene glycol oxidation in alkaline medium were studied by cyclic voltammetry, CO stripping voltammetry and chronoamperometry tests. XRD technique was applied to physical characterization and it was observed the formation of alloy. The average crystallite size was calculated from the Scherrer equation. The Pt92Rh7Ni1/C electrocatalyst shows a larger electrochemically active area and consequently higher catalytic activity for EG oxidation. This response was attributed to improvement in the synergistic effect provided by the reduction of the amount of Rh and Ni in the ternary alloy when compared to Pt80Rh15Ni5/C and Pt/C ETEK electrocatalysts. However, Pt80Rh15Ni5/C electrocatalyst showed greater tolerance to poisoning by intermediate species due to the presence of Rh in greater quantity, leading to a formation of adsorbed OH species in potentials smaller than those for platinum.

In this study, biogenic SiO2 of high purity and high surface area obtained from rice husk was used for prepare a nanostructured SnO2/SiO2composite. The predominantly amorphous silica was extracted in an acidic route and then the nanocomposite was done via sol-gel route using ethylene glycol and citric acid followed by heat treatment. SiO2 content of the rice husk was determined by X-ray fluorescence (XRF) and its specific surface area determined by nitrogen adsorption. The composite nanostructured SnO2/SiO2 was structurally characterized by the techniques of X-ray diffraction (XRD), Raman and Fourier transform infrared (FT-IR) spectroscopy. The morphological characteristics were revealed by scanning electron microscope (SEM).