Últimos itens adicionados do Acervo: Laboratório Nacional de Energia e Geologia

O Laboratório Nacional de Energia e Geologia (LNEG) é uma instituição de I&D orientada para responder às necessidades da sociedade e das empresas. Apostando numa investigação sustentável e para a sustentabilidade através da geração do conhecimento em Portugal.

Página 1 dos resultados de 2312 itens digitais encontrados em 0.002 segundos

Electrochemical impedance spectroscopy modeling using the dis-tribution of relaxation times and error analysis for fuel cells

Lopes, Vitor V.; Rangel, C. M.; Novais, Augusto Q.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
This paper proposes a new approach to determine the distribution of relaxation times (DRT) directly from the electro-chemical impedance spectroscopy (EIS) data, i.e. without the use of an equivalent electrical circuit model. The method uses a generalized fractional-order Laguerre basis to represent EIS where both the parameters of the basis and their co-efficients are estimated by solving a nonconvex minimization problem. Furthermore, the DRT confidence region is de-termined to assess the accuracy and precision of the DRT estimate. The approach is applied to analyze the dominant dynamic properties of an open-cathode hydrogen fuel-cell under different current and air-flow conditions. Results showed that the estimated DRT closely reconstructs EIS data even when there is a higher variance at smaller relaxation times.

Experimental and modeling studies of a micro direct methanol fuel cell

Falcão, D. S.; Rangel, C. M.; Pinto, A. M. F. R.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
The Direct Methanol Fuel Cell (DMFC) has attracted much attention due to its potential applications as a power source for transportation and portable electronic devices. Based on the advantages of the scaling laws, miniaturization promises higher efficiency and performance of power generating devices and the MicroDMFC is therefore an emergent technology. In this work, a set of experiences with a MicroDMFC of 2.25 cm2 active area are performed in order to investigate the effect of important operating parameters. Maximum power density achieved was 32.6 mW/cm2 using 4M mehanol concentration at room temperature. Polarization curves are compared with mathematical model simulations in order to achieve a better understanding of how parameters affect performance. The one-dimensional model used in this work takes in account coupled heat and mass transfer, along with the electrochemical reactions occurring in a direct methanol fuel cell and was already developed and validated for DMFC in previous work [1-3]. The model is also used to predict some important parameters to analyze fuel cell performance, such as water transport coefficient and methanol crossover. This easy to implement simplified model is suitable for use in real-time MicroDMFC simulations.

The effect of chloride as catalyst layer contaminant on the degradation of PEMFCs

Paiva, T. I.; Hashimoto, T.; Plancha, Maria João; Thompson, G. E.; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
In this work, the effect of chloride as a catalyst contaminant was studied on the performance and durability of a low power open-cathode fuel cell, intended for passive management of water. In an ex-situ study, cyclic voltammetry was used to assess the redox behaviour of platinum in chloride contaminated solutions at room temperature.The cell was operated integrating a range of relative humidity (RH) from ~30 to 80% and temperatures from 5 to 55 ºC. Results indicated that 60% RH is associated to maximum fuel cell performance over the studied temperature range. An examination of the fuel cell components after 100 h of operation revealed that chloride contamination has produced cathode failure associated to catalyst migration favored by operation conditions that allowed platinum particles to break free from their carbon backing and migrate toward the polymer electrolyte. Migration resulted in precipitation with larger mean particle size distribution within the solid electrolyte when compared to the original catalyst layer, rendering a very significant loss of thickness in the cathode material.

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

Silva, R. A.; Soares, C. O.; Carvalho, M. D.; Jorge, M. E. Melo; Gomes, A.; Pereira, M. I. da Silva; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
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...

Electrochemical behaviour of ionic liquid functionalized carbon supported Pt-Ru catalysts 

Esteves, M. Alexandra; Sá, A. I. Correia de; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Ionic liquid (IL) functionalized carbon supported nanocatalysts, including platinum-ruthenium catalysts, have been under investigation to achieve better catalytic performance on polymer electrolyte membrane fuel cells. Ionic liquids have particular physical properties, which usually improve the stabillity and dispersion of metal nanosized particles, providing an increase of the electrochemical active surface area. In this work, the synthesis and the electrochemical behaviour of two new ionic liquid functionalizated carbon supported Pt-Ru nanocatalysts is investigated regarding the methanol oxidation reaction. Preliminary obtained results show that IL functionalization of carbon can produce supported catalysts with improved performances depending on the ionic liquid and on the reduction process used to produce the catalyst nanosized particles.

Enhancing Pt electrocatalytic activity by surface functionalization of carbon support with aromatic sulphonic groups

Capelo, Anabela; Esteves, M. Alexandra; Sá, A. I. Correia de; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Preliminary results are presented for Pt deposited on 4-aminobenzenesulphonic acid-functionalized carbon, Pt/C_ABSA. Vulcan XC-72R was functionalized with the objective of influencing the dispersion of catalyst nanoparticles and to decrease the resistance of three phase boundaries, by introducing sulphonic groups. Electrochemical characterization of the supported catalyst was done in a 0.5 M sulphuric acid solution with added chloride and also using methanol demonstrating well defined features and stable voltammograms after 30 cycles, with apparent higher currents when compared with commercial catalyst. The structure sensitive adsorption of anions on platinum is confirmed by the blocking effect of chloride ions in the hydrogen adsorption-desorption region as well as by the consequent dissolution of platinum, evident in both anodic and cathodic features of the voltammograms regarding surface oxide formation and reduction. The partial reversibility of the effect of chloride ions is discussed. Research is in progress in order to accomplish a comprenhensive characterization of the synthesized catalyst and to ascertain the effect of the sulphonic groups.

Kinetics of sodium borohydride hydrolysis in aqueous-basic solutions

Retnamma, Rajasree; Rangel, C. M.; Novais, Augusto Q.; Matthews, Michael A.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kinetics. The estimation of kinetic parameters is performed by gPROMS (general PRocess Modeling System) parameter estimation tool. The reaction kinetics differs from low to highly-concentrated NaOH solutions. In highly-basic (.10 wt% NaOH), aqueous solutions of NaBH4, the rate is independent of NaOH concentration, while for lower-basic (< 10 wt% NaOH) solutions, the dependence is -0.57, confirming the inhibition of hydrolysis kinetics by NaOH.

A dynamic two phase flow model for a pilot scale sodium borohydride hydrogen generation reactor

Sousa, T.; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
A two-dimensional, non-isothermal, and dynamic model was developed to describe a sodium borohydride/hydrogen re-actor for stationary use. All relevant transport phenomena were treated in detail and the kinetic model developed previ-ously by the authors was introduced into the algorithm. In this paper the reactive solution was modeled as a two phase flow; with this approach the impact of the hydrogen production on the solution stirring could be observed and quantified. Results showed that not all ruthenium deposited on the nickel foam was used efficiently as catalyst. In fact, most of the reaction occurred in the surface of the catalyst foam and around 70% of the deposited catalyst was not used. It was also demonstrated the importance of the two phase flow approach for a correct simulation of the solution stirring and heat transfer.

Conversion of carbon dioxide into fuel by electrochemical reduction in aqueous solvents

Pardal, T.; Fernandes, T. R. C.; Machado, A. S. Reis; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
he mission of Omnidea, a Portuguese SME is to perform leading edge R&D in innovative energy concepts. In collaboration with Research Institutes Omnidea is developing a technology based upon a regenerative energy storage cycle. In this cycle the recharge system converts CO2 into hydrocarbons using a renewable source of power. The discharge system produces electrical energy when hydrocarbons and oxygen from the recharge system are directly supplied to a device such as a Solid Oxide Fuel Cell (SOFC). This work focuses on the challenges involved in the task of bringing this technology closer to the market. A key feature of this technology is the use of copper which is known to have unique properties for converting CO2 electrochemically into hydrocarbons. The modification of copper electrodes with copper deposits to improve the catalytic activity and selectivity of the cathodes in the production of hydrocarbons in aqueous solvents is also described.

Redox stability and bifunctionality of LaNiO3-based oxygen electrodes

Silva, R. A.; Soares, C. O.; Carvalho, M. D.; Jorge, M. E. Melo; Gomes, A.; Rangel, C. M.; Pereira, M. I. da Silva
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
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...

Comparison of microalgal biomass profiles as novel functional ingredient for food products

Batista, Ana Paula; Gouveia, L.; Bandarra, Narcisa M.; Franco, J. M.; Raymundo, Anabela
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2013 ENG
Microalgae are one of the most promising sources for new food and functional food products, and can be used to enhance the nutritional value of foods, due to their well-balanced chemical composition. Knowing their physicochemical characteristics is fundamental for the selection of the most suitable microalgae to specific food technology applications and consequently successful novel foods development. The aim of this study is to screen the chemical composition (e.g., proteins, pigments, fatty acids) and thermogravimetry properties of five microalgae species with potential application in the food industry: Chlorella vulgaris (green and carotenogenic), Haematococcus pluvialis (carotenogenic), Spirulina maxima, Diacronema vlkianum and Isochrysis galbana. C. green and S. maxima presented high protein (38% and 44%, respectively), low fat content (5% and 4%, respectively). The carotenogenic C. vulgaris and H. pluvialis showed a higher carotenoid content, higher fat, low protein and better resistance to thermal treatment. D. vlkianum and I. galbana presented high protein (38–40%) and fat (18–24%) contents with PUFA's?3, mainly EPA and DHA. Finally, the results from microalgae chemical and thermal analysis were grouped and correlated through Principal Components Analysis (PCA) in order to determine which variables better define and differentiate them.

Liquid-Liquid Extraction of Platinum from Chloride Media by N,N'-Dimethyl-N,N'-Dicyclohexyltetradecylmalonamide

Costa, M. Clara; Assunção, Ana; Costa, Ana M. Rosa da; Nogueira, C. A.; Paiva, A. P.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em //2013 ENG
Liquid-liquid extraction of platinum(IV) from chloride media was carried out using N,N'-dimethyl-N,N'-dicyclohexyltetradecylmalonamide (DMDCHTDMA) in 1,2-dichloroethane. Platinum can be effectively extracted by DMDCHTDMA without addition of tin(II) chloride, since extraction percentages (%E) of 88% and 99% have been achieved from 6 M and 8 M HCl, respectively. Moreover, platinum can be successfully stripped through a simple contact with a 1 M HCl solution. The effect of some experimental parameters such as equilibration time, diluent, extractant and HCl concentrations was systematically investigated. The loading capacity of DMDCHTDMA was also evaluated. Data obtained from successive extraction-stripping cycles suggest a good stability pattern of DMDCHTDMA. Preliminary extraction data achieved with single metal ion solutions pointed out to a possible separation of platinum(IV) from palladium(II).

New phosphonic acids and esters derived from Indazole: synthesis and biological activity evaluation

Afonso, S. S.; Teixeira, A. P. S.; Martins, M. R.; Teixeira, Fátima C.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Bisphosphonates (BPs) are a group of compounds derived from bisphosphonic acid and their salts, with a P-C-P structure which confers higher metabolic and chemical stability. They are an important class of drugs with therapeutic applications in the treatment of diseases of bone mineral metabolism such as osteoporosis and Paget's disease. These compounds have also shown activity in other areas, such as antitumor and antiparasitic activities.1 The use of these compounds in therapy is affected by their low oral bioavailability due to low lipophilicity and the presence of charges at physiological pH. The improvement of their pharmacokinetic properties can be obtained by the use of ester derivatives as prodrugs.2 In this work, we present the synthesis and characterization of various phosphonic acids and esters derivatives of indazole (Figure 1). The biological activity of these compounds were evaluated including their toxicity, antioxidant and antimicrobial activities.3 Bisphosphonic acid derivatives showed broad spectra with high activity against Gram – and Gram + pathogenic and commensal bacteria. These compounds also present antioxidant activity by the â-carotene/linoleic acid method.

Indicadores geológicos e ambientais para o ordenamento da actividade extractiva : o caso do Anticlinal de Estremoz, Portugal

Carvalho, Jorge M. F.; Falé, Patrícia
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2008 POR

O planeamento sectorial da indústria extractiva e sua importância para os instrumentos de ordenamento do território : o caso de Portugal

Falé, Patrícia; Mendonça, Alexandra
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2008 POR

Stochastic modelling and probability risk maps of nitrate pollution in the vicinities of Beja, Alentejo, south Portugal

Paralta, Eduardo; Ribeiro, Luís F.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2001 ENG
The groundwater resources study of the Alentejo region (CCR Alentejo, 1996-1999) was carried out in several places namely Beja's Gabbros Aquifer to assess water quality for public supply and agriculture. A geostatistical study of nitrate diffuse pollution in the vicinities of Beja based on probabilistical technics was developed in the context of a MSc Thesis in co-operation with CVRM - Geosystems Center. Several basic statistics between July 1997 and July 2000 were computed. Indicator variograms for nitrate ion with 50 mg/l cut-off are presented and Indicator Kriging is performed based on parameters fitted to spherical models. Risk and probability maps used in environmental management are also included.

Environmental impact assessment of the penetration of hydrogen technologies in Portugal's road transport

Travassos, Maria Antónia; Sá, A. I. Correia de; Luz, Paulo P. da; Rangel, C. M.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em 01/04/2009
Road traffic is one of the transportation sectors with faster growth and also one of the most important emitters of greenhouse gases (GHGs). In this work, an analysis of the environmental benefits resulting from the introduction of hydrogen on road transport in Portugal is made. Impact is analyzed mainly looking at the pollutant emissions provided by road transport at the point of use. Emissions associated to road transport have been estimated using the software COPERT (version 4), since it provides a detailed methodology for each specific pollutant related to the vehicle fleet of a region or country, as well as the driving conditions and fuel consumption. Passenger cars, light duty vehicles and public transport buses are the vehicles categories in which the hydrogen technology is foreseen. The hydrogen penetration rates (moderate and high) are extracted from the European Project HYWAYS. Two trends are then considered, which give penetration rates of 40.0 % and 74.5 % in 2050 for the moderate and high scenarios respectively.

Scientific collaboration within and accross research teams

Correia, Zita; Cera, Rosália; Egreja, Catarina
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2009 ENG
This paper presents part of the results achieved to date in the process of developing a collaboratory in two R&D organizations. A collaboratory corresponds to a laboratory without walls, in which scientists are connected to each other, to scientific instruments and to information, independently of time and location. These two cases are part of a broader research project engaged in building a collaboratory in order to share knowledge and resources among the Portuguese State Laboratories. The building of the collaboratory is anchored on three main tasks: a) information audits carried out in each of the organizations, in order to map the main information flows, entities, repositories and systems; b) information behaviour research, in order to gain insight into the organizational information culture and the researchers' information use; c) implementation of the appropriate infrastructure and tools, in order to accommodate information archiving and intelligent search, collaborative software, remote control of scientific instruments, and multi-channel access to the services. The case study strategy was adopted because it is particularly amenable to the triangulation of methods (namely document analysis, survey and interviewing) thus providing rich ingredients to characterize a specific context. Discourse analysis was the technique used to analyse the interview transcripts. The research sites are two government R&D institutions operating in the Civil Engineering and in the Nuclear Technology fields...

FTIR, a powerful technique in organic coatings failure diagnosis

Costa, Maria do Rosário; Santos, M. Teresa; Diamantino, Teresa C.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em 08/09/2009 ENG
FTIR spectrometry (Fourier Transform Infrared) is an instrumental technique of analysis that presents significant advantages on the dispersive traditional system, such as the increase of the relation signalnoise, the capacity of getting absorption spectra of low energy and therefore, bands of absorption of weak intensity. This technique is widely used in study, resin characterization and evaluation of polymeric materials as well as of its degradation when exposed to the most varied conditions of service, or still in the analysis and diagnosis of defects that occur during the application or production process. Techniques connected to the FTIR had more recently appeared as the photoacoustic (PAS-FTIR), the microscopy (MCT-FTIR) and the attenuated total reflectance (ATR), which allow to analyze weekly transparent and dark samples without removal of coatings from the substrates. The choice of the technique to use depends on the morphology of the surfaces to analyze and the type of failure in cause (lack of adhesion, contamination, aging degradation, etc). In this work the application of FTIR and techniques associates to the identification of the causes that had originated diverse types of defect in applied organic coatings on polymeric materials is presented. Key words: FTIR...

Towards sustainable Summer comfort

Laia, Carlos; Richard, Mathieu; Camelo, Susana; Gonçalves, Helder
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em /04/2009 ENG
There is a growing energy demand for cooling in European buildings. It is expected that the cooled floor area will be four times higher in 2020 when compared with 1990 figures. Cooling is already the energy use in the building sector with the highest increase rate. This evidence is not contributing to the overall objective of reduction CO2 emissions. The conventional answer to this problem is to improve of the energy efficiency of cooling. However, this strategy showed limited results in terms of saving energy and reducing greenhouse gas emissions. In fact, cooling can be avoided (or the need to use energy for cooling) or significantly reduced without risking summer thermal comfort for building occupants, having thus the potential to achieve substantial reductions in energy demand. However, avoidance or even major reduction of cooling implies a new approach in building design, construction and operation phases. Different scientific and technological advances shall coherently be used and be offered to building promoters or building owners as a new service. The new adaptive comfort theory, the possibility for local adaptation for building users and facilities, the capability to intervene in the surrounding urban environment, the use of mature passive cooling solutions...