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Antioxidants are an alternative to prevent or retard biodiesel degradation. Soursop (Annona muricata L.) is a native tropical fruit with important antioxidant activity, besides high concentration of phenolic compounds. Peels form about 20 % of the soursop fruit composition and are usually discarded as a waste product. In this study the antioxidant potential of different peel extracts was evaluated by oxidative stability when used as an additive into soybean biodiesel. All samples were analyzed by the Rancimat® 873, using 32 experimental design. The tests were performed with biodiesel B100 with solutions extracted in different conditions, such as pH and residue concentrations. Results demonstrated that all experiments were able to increase significantly the induction period (IP), when compared to a pure biodiesel control sample, and showed similar efficiency with synthetic antioxidants (BHT). Among all experiments, each neutral and alkaline extractions presented induction periods over 8 h, achieving and surpassing the minimum allowed by European standard. However, the highest IP was found to be 10.30 h, with 3 g L-1 in neutral extraction. Results corroborate that soursop peel has a high antioxidant capacity and efficiency to improve the oxidation stability, and could be used as an inexpensive natural antioxidant to biodiesel.

Carbon steel is one of the most widely used alloys in industrial applications. However, the use of this metal may be limited because of corrosion tendency. Thus, it is necessary to develop methods that inhibit its degradation. One way to inhibit corrosion is to use organic inhibitors. Some organic compounds with heteroatoms inhibit corrosion by forming a protective film. In this study, the corrosion inhibition of carbon steel 1020 in 0.1 mol L-1 hydrochloric acid medium was evaluated. The natural inhibitor used was an aqueous extract of the bark of Persea pyrifolia (PP) plant at concentrations of 2.5, 5 and 10% V / V. The electrochemical response was determined by open circuit potential measurements, electrochemical impedance spectroscopy, and anodic potentiodynamic polarization. Therefore, mass loss was measured, and inhibitory efficiency was evaluated. The best results were observed for the concentration of 2.5% V / V of Persea pyrifolia extract, presenting and inhibition efficiency of 82.5% on the 1020 carbon steel. The electrochemical results indicates that PP extract can be used as green corrosion inhibitor in acidic medium. DOI: http://dx.doi.org/10.17807/orbital.v13i2.1469

Dye-sensitized solar cells (DSSC) are devices to solar energy conversion, which present low production costs and high photoelectrochemical stability. The aim of this study was to investigate the synthesis of TiO2 by Pechini methodology, using C12H28O4Ti and TiCl3 as precursors, and their application in solar cell sensitized by N719 dye. The characterization techniques employed were Scanning Electron Microscopy (SEM), UV-VIS Spectroscopy, X-ray diffraction (XRD), photochronoamperometry, j-V Curves and EIS plots. The results demonstrated a high crystallinity and surface area to particles obtained with C12H28O4Ti as precursor. The highest photoconversion energy efficiency reached was to TiO2 using C12H28O4Ti with PCE= 4.17±0.13% with photoelectrochemical parameters of jsc= 5.53 ±0.08, Voc= 0.78±0.07 FF=0.58±0.05 and less resistive to charge transport with τe= 53 ms. DOI: http://dx.doi.org/10.17807/orbital.v13i2.1446

Renewable energy methodologies are the key to a sustainable future. PV technology has been raised as one of the most promisor alternatives for energy conversion, due to the use of an inexhaustible source. The third generation of solar devices, present in composition a semiconductor oxide, that work as electron transport material (ETL), receiving and transporting the electron from a photosensitive molecule. TiO2 performs with efficiency the role of ETL in solar devices, nevertheless, since of the higher cost, other oxides have been studied, as Nb2O5. This work aims to synthetized Nb2O5 by Pechini methodology and applied it as ETL in a solar device. The techniques performed in particle characterization were Scanning Electronic Microscopy (SEM) and X-ray diffraction (XRD). To verify the capability of transport electrons, the electrochemical measurements were applied to Voc/Jsc decay, j-V curves, Electrochemical Impedance Spectroscopy (EIS), and Intensity Modulate Photovoltage Spectroscopy (IMVS). The results showed Nb2O5 synthesized in orthorhombic phase able to produce a photosensitive dye-solar device with j = 4.18 mA cm−2, V = 825 mV, FF = 0.4, PCE = 1.38% with slow recombination rate when compare to TiO2 dye-solar cell. The IMVS and EIS technique present the same accuracy to electron lifetime determination which is confirmed by the t-test performed.

O desenvolvimento humano esta relacionado com a descoberta de novas fontes de energia. Por outro lado, esta busca conduziu a severas mudancas climaticas e danos ao meio ambiente, que acabou sendo o foco de pesquisa do seculo. Aquecimento global, chuva acida, deplecao da camada de ozonio dentre outros problemas ambientais, conduziram ao desenvolvimento de metodologias alternativas de energia. A celula solar e um dos dispositivos mais promissores para a reducao da queima de combustiveis fosseis, por utilizar um recurso energetico inesgotavel. Celulas solares sensibilizadas por corante (CSSC), desde descobertas por Gratzel e colaboradores, tem apresentado grande foco de estudo, devido ao baixo custo de producao, boa eficiencia e facil producao. Estas, sao fabricados pelo uso de um material semiconductor, um corante com alto coeficiente de extincao molar, um intermediador de cargas e um material com atividade catalitica. As mais variadas metodologias eletroquimicas de caracterizacao vem sendo utilizadas para entender o principio operacional destes dispositivos. Neste trabalho e apresentado uma revisao no campo das CSSC, os materiais utilizados, o principio operacional, os avancos tecnologicos e as mais diversas tecnicas de caracterizacao utilizadas

Celulas solares sensibilizadas por corante (CSSCs) sao uma nova geracao de dispositivo fotovoltaicos capazes de absorverem luz solar e converter em eletricidade. As CSSC utilizam em sua composicao oxidos semicondutores nanocristalinos, principalmente o dioxido de titânio (TiO 2 ), sensibilizados por corantes rutenados. Atualmente, busca-se o a modificacao do TiO 2 com particulas que sejam capazes de aumentar a eficiencia desta celula. O objetivo deste trabalho e estudar a influencia das variaveis do processo de sintese de particulas de oxido de cerio (CeO 2 ), visando a aplicabilidade em celulas solares sensibilizadas por corante N719. O CeO 2 foi obtido pelo metodo por precipitacao. Foi aplicado delineamento fatorial incompleto Box-Behnken (3 3 ), para as variaveis: concentracao de Ce(NO 3 ­) 3 .6H 2 O (mol.L -1 ), temperatura do meio reacional (°C) e tempo de reacao (h). As particulas foram caracterizadas por medidas de espalhamento de luz (DLS), analise por difracao de raios X (DRX), microscopia eletronica de varredura (MEV). O CeO 2 foi aplicado na celula solar juntamente com dioxido de titânio (TiO 2 )e os parâmetro fotovoltaicos foram extraidos. A otimizacao resultou em uma concentracao de Ce(NO 3 ) 3 .6H 2 O igual a 0,1 mol.L -1 , tempo de reacao de 18 h e temperatura de 80 °C, onde o menor valor medio para a particula foi de 99,30 nm. Os ensaios eletroquimicos evidenciaram que a amostra contendo diâmetro de particulas menores TiO 2 +CeO 2 100nm , apresentou uma eficiencia de conversao de energia solar, cerca de 30% maior, que as particulas de diâmetros maiores ( TiO 2 +CeO 2 1000nm ).

Poly(3-alkylthiophenes), P3AT, are organic polymers formed by conjugate structures with conductive properties. Zinc oxide (ZnO) has been used as an electron acceptor in hybrid solar cells because it offers electron transport properties and can be synthesized by methods in which the variation of synthesis parameters allows morphological control. Different ZnO morphologies allow for distinct properties in terms of electronic transport at the interface of solar cells. ZnO particles were synthesized by the co-precipitation method. ZnO films were deposited by spin-coating in Fluorine Tin Oxide (FTO) and then immersed in solutions containing poly (3-hexylthiophene) (P3HT) or poly (3-octylthiophene) (P3OT) polymers. The cell was assembled in the form of a sandwich consisting of: FTO/ZnO,P3AT/Iˉ,I3ˉ/Pt/FTO. UV-vis measurements were performed for bandgap calculation, scanning electron microscopy (SEM), X-ray diffraction (XRD), and J-V curves. The ZnO/P3HT cell presented the best values of J, V and η, indicating an improvement in the electronic transfer processes, with a value of η = 0.56%. DOI: http://dx.doi.org/10.17807/orbital.v13i2.1451

Renewable energy sources have received much attention in recent years due to concerns about global climate and environmental changes. Solar energy appears to be a promising alternative, especially dye-sensitized solar cells (DSSC), which, according to the literature, can achieve a power conversion efficiency in excess of 11%, depending on the semiconductor oxide used in their fabrication. The aim of this paper is to investigate the performance of DSSCs using cerium oxide (CeO2), titanium oxide (TiO2), and commercial dye N719. CeO2 was obtained using the Pechini and precipitation methods. The characterization techniques employed were x-ray diffraction, Raman spectroscopy, scanning electron microscopy, ultraviolet–visible spectroscopy, dynamic light scattering, and photoelectrochemical measurements. The results indicate that the efficiency of the DSSC CeO2/TiO2 obtained using the precipitation method was about 20% higher than that of the DSSC TiO2.

In this study, it was investigated the photovoltaic parameters of Dye Sensitized Solar Cells (DSSC) and the thin coating morphology of TiO2 by Doctor Blading and Spin Coating methods, sintered at 450 ºC and 450 ºC with a heating rate of 0.4 ºC s-1, using a natural dye extract from Hibiscus. These properties were studied by scanning electron microscopy (SEM), photochronoamperometry and curves j-V. It was demonstrated that all solar cells produced are photosensitive with an excellent charge injection. The cell with a better energy conversion (jsc = 0.53 mA cm-2; Voc= 0.471 V and FF= 0.518), uniform and flawless morphology was obtained to cell coated by Doctor Blading method, with a heat treatment of 450 ºC/0.4 ºC s-1. DOI: http://dx.doi.org/10.17807/orbital.v10i3.1101

Mix of oxides is an alternative method to enhance the photoelectrochemical parameters of solar devices. Nb inserted in TiO2 was prepared successfully by Pechini methodology and the oxide was used as electron transport material in P3HT organic solar device. TiO2 anatase/rutile was confirmed by XRD measurement and band gap determination combined with cyclic voltammetry measurement indicated the Nb sub states creation above TiO2 conduction band. IMVS and OCP decay diagram showed an increasing in electron lifetime of 0.4758 s–0.6645 s to the cell containing Niobium. The energy conversion efficiency to the cell based in 5% of Nb presented an improving about 25% when compared to bared TiO2, proving that this methodology is a promisor route to produce enhanced electron transport materials.

Celulas solares sensibilizadas por corante (CSSC) sao dispositivos que aproveitam a luz do sol para gerar energia e possuem na composicao um oxido semicondutor e um fotossensibilizador adequado. Devido ao custo elevado, a pesquisa por novos materiais aplicados nas celulas solares desperta grande interesse. Este trabalho tem como objetivo estudar celulas solares hibridas de interface FTO/TiO2/corante produzidas com diferentes fotossensibilizadores naturais de baixo custo, extraidos em solucao etanoica acidificada, de diferentes produtos naturais: ameixa, uva, urucum e berinjela. As tecnicas de caracterizacao utilizadas foram: Espectroscopia na regiao do ultravioleta-visivel (UV-VIS), Espectroscopia na regiao do Infravermelho por Transformada de Fourier (IV-TF), medidas do Potencial de Circuito Aberto em funcao do tempo (Eca), curvas Fotocronoamperometricas (FCA) e Curvas de Densidade de Fotocorrente em funcao do Potencial (j-E). Os corantes testados nas CSSC apresentaram caracter de fotossensibilidade, com adsorcao nos filmes de TiO2 e absorcao maxima na regiao do visivel. A CSSC com melhores parâmetros fotovoltaicos foi empregando-se o corante extraido da ameixa, gerando uma celula solar com ƞ = 0,12±0,03, Eca = 572±12 mV, FF = 0,57±0,01 e jcc = 0,40±0,09 mA cm-2.

Investment in renewable energy sources has increased in recent decades because of the environmental impact caused by the non-renewable energy sources burning. Regarding to the available renewable energy technologies, the conversion of solar energy into electrical energy using photovoltaic devices, especially dye-sensitized solar cells (DSSC), stands out. In this study, we investigated the recombination reactions of DSSCs containing ZnO and Nb2O5 using electrochemical impedance spectroscopy, intensity modulated photovoltage spectroscopy, intensity modulated photocurrent spectroscopy, and charge extraction. The addition of Nb2O5 to the ZnO cells reduced recombination effects, and the 5% Nb2O5 cell presented the best photovoltaic parameters, having an electron lifetime of 0.18 s, collection time of 0.01 s, and efficiency of 2.39%.

Hybrid inorganic-organic solar cells are an attractive alternative energy source because of their low-cost production and ability to make use of a large amount of solar radiation available. This work aims to evaluate different solar cells composed of TiO2 and ZnO with P3OT/P3MT copolymer. Layers of semiconductor oxides were deposited on transparent fluorine-doped tin oxide (FTO) by spin coating and adsorption in the polymer solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), were used to characterize the fabricated semiconductors and curves of current density vs. potential (j-V), photochronoamperometry (j-t) and electrochemical impedance spectroscopy (EIS) were used to determine their electrical characteristics. The XRD analyses confirmed the crystalline nature of the oxide materials. SEM micrographs showed the spherical morphology of ZnO and the poorly defined agglomerate morphology of TiO2. The electrochemical measurements proved that the best cell was produced with P3OT/P3MT copolymer and TiO2, owing to its lower charge transfer resistance, with the following photovoltaic parameters: Voc = 0.615 V ± 0.004, jsc = 1.545 mA cm-2 ± 0.240, FF = 0.637 ± 0.003, and η = 0.617% ± 0.117.

Hybrid solar cells show an increasing number in researches due to its low cost and easy of production. They are composed by and organic material and a semiconductor oxide. The aim of this paper was to synthesis and characterize zinc oxide by coprecipitation and apply it in a hybrid solar cell that uses a P3HT/P3OT copolymer as charge carrier. The cell was assembled in "sandwich" form using FTO/ZnO/P3HT-P3OT as work electrode, (Pt/FTO) as conter electrode and I/I-3 redox couple as electrolyte. Through the X-ray diffractogram the formation of a single ZnO wutzite hexagonal phase was observed. The morphology obtained for the oxide was spherical. The results of photochronoamperometry showed current density values of jP3HT/P3OT =0.55 mA.cm-2 for the cell in the presence of the copolymer and the curve jxV showed an efficiency of 0.16% for the studied cell, demonstrating that the polymer was a satisfactory sensitizer.

Natural dyes can be used in dye sensitized solar cells (DSSCs) to generate low-cost devices, although with low light harvesting because of energy losses from the recombination process. This study investigates recombination reactions in DSSCs with natural dyes extracted from eggplants, plums, and hibiscus flowers. Titanium dioxide films were coated on a fluorine-doped tin oxide glass conductor substrate by the doctor blading method and impregnated in a dye solution for 24 h. Electrodeposited platinum was used as the cathode, and I3–/I– as the redox couple. The techniques employed were: intensity modulated photovoltage spectroscopy, intensity modulated photocurrent spectroscopy, electrochemical impedance spectroscopy, charge extraction, and cyclic voltammetry. The results show that cells containing plum dye exhibited the best photovoltaic parameters, with high values of gap, charge extraction, and potential, being less resistive to charge transfer with an electron lifetime of 0.51 s, collection time of 8.54 ms, and charge efficiency collection of 0.99.

Dye-sensitized solar cells using natural dyes have lower cost when compared to ruthenium-based dyes. This paper aims to evaluate, electrochemically, solar cells composed of TiO2 with dye extracted from the Hibiscus(var. Sabdariffa) and propose an adsorption model capable of predicting the adsorption mechanism of the dye on the semiconductor surface. The characterization techniques used were: Fourier Transform Infrared Spectroscopy, UV-VIS Spectroscopy, Measurement of the Open Circuit Potential, Photocronoamperometry, and Current Density Curves vs. Potential. The infrared spectroscopy confirmed there was adsorption of dye on the TiO2 surface. The adsorption isotherm with the better value of linear coefficient (R= 0.9874) was the Langmuir isotherm. The electrochemical techniques showed that the best cell prepared from a solution with a concentration of 5.27 mg L-1 of the natural dye, had an Eca= 516 mV, j = 0.15 mA cm-2 and an energy efficiency (η) of 0.15%.