Conhecendo espécies de plantas da Amazônia: ingá-costela (Inga capitata desv. - Leguminosae).

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Conhecendo espécies de plantas da Amazônia: imbaúba-vermelha (Cecropia palmata Willd. - Urticaceae).

bitstream/item/81613/1/Oriental-ComTec238.pd

Conhecendo espécies de plantas da Amazônia: ingá-vermelha [Inga alba (Sw.) Willd. - Leguminosae - Mimosoideae].

bitstream/item/99944/1/COM-242.pd

Improving electrocatalityc activity of LaNiO3 films by deposition on foam nickel substrates

The electrodes were obtained by coating a nickel foam support with the oxide suspension. Optical microscopy and cyclic voltammetry were used on the electrodes characterization. The evaluation of the electrodes electrocatalytic activity, towards the oxygen evolution reaction in alkaline medium, was performed by means of steady state measurements. The reaction follows a first order kinetics, with respect to OH- concentration, with Tafel slopes close to 40 mV, for low overpotentials. Based on the apparent and real current densities it was possible to conclude that the increase on the electrode activity, when compared with the published data, is mostly related to geometric factors. This fact has been associated with the high electrode/electrolyte contact area provided by the foam nickel substrate. Synergetic effects between the Ni foam and the perovskite oxide cannot be discarded

Redox stability and bifunctionality of LaNiO3-based oxygen electrodes

One key issue in the development of Regenerative fuel cells (RFCs) is the availability of cheap, highly active electrocatalysts for both oxygen reduction and water oxidation. Perovskite-type oxides, with the general formula ABO3, are potential catalysts for next generation of regenerative fuel cells. In particular, LaNiO3 has been recognised as one of the most promising oxygen electrodes. In this work LaNiO3 perovskite-type oxides, prepared by a self-combustion method [1, 2], have been simultaneously optimized for activity and stability as an anode and cathode material for water oxidation and oxygen reduction reaction (ORR), respectively. Extremely high surface area has been measured by BET analysis with matching electrochemical activity estimated by cyclic voltammetry and electrochemical impedance spectroscopy. A full electrochemical study has been conducted in order to kinetically characterize the prepared electrodes in alkaline media, using a Ni foam and carbon paper as support material for the electrodes. For LaNiO3 deposits on Ni foam, low contact resistance between the oxide and support, possibility of high metal oxide loadings and dimensional stability were accomplished with remarkable stability in the region of oxygen evolution. For LaNiO3 deposits on carbon paper, the preparation of porous gas-diffusion electrodes providing extended reaction zones in the solid/liquid/gas interfacial region. This type of electrode was reserved for the region of oxygen reduction in which good results were obtained, since for water oxidation the electrochemical oxidation of carbon sets a practical limit to the lifetime of the carbon supported catalysts. The electrode's stability study was performed by potential cycling and at constant current density in the appropriate potential windows

Towards stable bifunctional oxygen electrodes and corrosion resistant gas diffusion layers for regenerative fuel cells

ABSTRACT: Regenerative fuel cells (RFCs) can provide very high energy storage at minimal weight in a dual mode system, by combining an electrolyzer and a fuel cell. Although RFCs are an appealing technology their development is still at an early stage. One key issue is the search for highly active electrocatalysts for both oxygen reduction and water oxidation. Presently, platinum is the best electrocatalyst for the oxygen reduction reaction (ORR), but has a poor oxygen evolution (OER) performance while metal oxides catalyze the OER but not the ORR. Yet, the search for the development of bi-functional oxygen electrodes is also associated to structurally stable gas diffusion layers - they must be capable of withstanding high potentials when cells are operated in the electrolyzer mode and in addition, mass transport limitations when used as a cathode in fuel cell mode. A novel approach is used in this work to tackle the issue, focussing on the development of stable gas diffusion electrodes for the oxygen reactions, having as a base high surface area LaNiO3. Previous work by the authors has optimised the synthesis of the mentioned perovskite-type oxide, prepared by a self-combustion method. The high electrochemical surface area and low porosity of the oxide has been indicated by electrochemical impedance spectroscopy (EIS) and BET measurements. A full characterization has been the subject of recent publications [1,2]. In a first instance, carbon diffusion electrodes on carbon paper are considered. The gas diffusion layers were prepared from carbon black Vulcan XC-72 R, with a LaNiO3 loading of 3 mg cm-2. To fabricate the catalyst layer, an ink was prepared by suspending LaNiO3 in isopropanol, and stirring in an ultrasonic bath to thoroughly wet and disperses it. A 5% Nafion® dispersion solution (Electrochem, Inc) was then added to the mixture. The catalyst inks were dispersed onto the gas diffusion layer with a brush, and dried at 50°C, until the desired catalys t loading was achieved. Finally, a Nafion layer was painted and dried at 50ºC. Significant current densities were obtained in both OER and ORR domains. A full electrochemical study was conducted in order to obtain the kinetic parameters in the OER region using a 1 M KOH solution. Cyclability and stability tests were also conducted. The tests were done in two potential ranges and served as a means of electrode conditioning. The electrode was also subjected to 200 cycles between 0.25 and 0.55 V vs Ag/AgCl (sat.) and an extra 100 cycles between -0.40 and 0.6 V vs Ag/AgCl (sat.), at a scan rate of 100 mV s-1. Additionally a constant current density of ~10 mA cm-2 was applied during 50 hours with simultaneous potential monitoring. Activity loss and increasing resistance of the electrodes were observed using cyclic voltammetry and EIS respectively. Carbon oxidation is favorable at the working potentials used which might sets a practical limit on the lifetime of the GDE. In a second instance, the deposition of LaNiO3 on a Ni foam (1.6 mm thickness, 95% porosity) was effected bringing about more stability in the OER region and Tafel slopes (47 mVdec-1) practically half of the value encountered in the case of carbon paper electrodes. Stability under galvanostatic conditions was assessed at current densities 10 times larger than those used in the case of the carbon paper (100 mA cm-2), also during 50 h, with excellent results. Due to the high stability at anodic potentials found with the Ni foam electrodes and in order to increase current densities, composite electrodes LaNiO3/Pt-Ru were prepared as an alternative to carbon paper electrodes. Results obtained using non-supported Pt-Ru (5-30 wt%) are discussed and compared with the case of carbon-supported Pt-Ru nanoparticles, in the same experimental conditions. It is suggested that LaNiO3 can be used as susbstitute material for carbon black, avoiding the effects of carbon corrosion in the OER region

LaNiO3-based catalyst in gas diffusion electrodes: activity and stability for oxigen reactions

Perovskite-type oxides are potential catalysts for next generation of regenerative fuel cells. In particular, LaNiO3 has been recognised as one of the most promising oxygen electrodes. In this work LaNiO3 perovskite-type oxides, prepared by a self-combustion method [1, 2], have been used for the preparation of porous gas-diffusion electrodes (GDE). Electrodes were prepared on Toray carbon paper (CP) substrates, consisting of a diffusion layer, a catalyst layer and a Nafion® layer. The gas diffusion layers were prepared using Vulcan XC-72R. The catalyst ink was prepared by suspending the material in isopropanol, stirring the mixture in an ultrasonic bath to thoroughly disperse it. Ink slurries were also pasted onto glassy carbon discs and used as working electrodes for full kinetic studies at potential domains for the oxygen reduction (ORR) and oxygen evolution (OER) reactions. A systematic study on the effect of the oxide loading (OL) on the electrodes surface area was done by cyclic voltammetry. It was found a quasi linear variation between the electrodes surface area and the oxide loading. Roughness values varying from 106±3 to 307±6 were obtained for OL between 1 and 5 mg cm-2 respectively. The results show that the peak current density increases with the increasing on oxide loading as shown in Fig. 1. Higher current densities for ORR were obtained for the electrodes prepared using LaNiO3-based perovskite with partial substitution of Ni by Cu. Stability studies of the GDEs, performed using a pre-defined cycling protocol in 1M KOH, will be discussed together with catalytic activity parameters relevant for their potential use as bifunctional oxygen electrodes

Effect of the oxide loading on the surface characteristics of LaNio3 oxide coated electrodes

The LaNiO3 perovskite-type oxide is one of the most tested anode for the oxygen evolution reaction in alkaline solutions. It is well established that the oxide preparation conditions and the electrode fabrication are key factors to control the electrochemical behaviour of oxide coatings. In a previous work the authors studied the influence of preparation conditions of the oxide and support type on the electrochemical behaviour of Ni foam coated LaNiO3 electrodes. Ni foam was selected as support due to its unique characteristics namely low contact resistance between the oxide and support, possibility of high metal oxide loadings and dimensional stability [1]. No studies were performed, concerning the influence of the oxide loading. Studies performed by Singh et al. on LaNiO3 coatings on Ni foil supports have shown that the electrode roughness factor increased with increase in oxide loading at the beginning and finally attained a constant value around 0.03 g cm-2 [2]. The present work reports on the study of the dependence of roughness factor (Rf) and morphology factor (φ) on the oxide loading for Ni foam coated LaNiO3 electrodes with loadings varying between 0.02 and 0.14 g cm-2. Cyclic voltammetry and electrochemical impedance spectroscopy were used to evaluate the Rf and φ values, complemented by optical microscopy observations. A non-linear increase of both Rf and φ with the oxide loading is observed, showing a level off when the oxide loading is increased. The level off was interpreted as a progressive exclusion of the crystallites from the contact with the solution as the oxide coating thickness increases