Browsing by Issue Date, starting with "2009-04-01"
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- Environmental impact assessment of the penetration of hydrogen technologies in Portugal's road transportPublication . Travassos, Maria Antónia; Sá, A.I. De; Luz, Paulo P. da; Rangel, C. M.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.
- MEA degradation and failure modes in PEM fuel cellsPublication . Silva, R. A.; Paiva Luís, Teresa; Rangel, C. M.The mechanisms of fuel cell degradation are not well understood. Even though the numbers of installed units around the world continue to increase and dominate the pre-markets, the present lifetime requirements for fuel cells cannot be guarantee, creating the need for a more comprehensive knowledge of material’s ageing mechanism. In this work, failure modes and mechanism of the membrane-electrode assembly (MEA) in PEM fuel cells are studied stressing the issues that may constrain stability, power and lifetime. Diagnostics methods and tools used for in-situ and ex-situ analysis of PEM fuel cells were used in order to better categorize irreversible changes in the kinetic and/or transport properties of the cell. Data for MEA degradation obtained during and after fuel cell ageing in extreme testing conditions will be discussed. Electrochemical Impedance Spectroscopy (EIS) is found instrumental in the identification of fuel cell flooding conditions and membrane dehydration associated to mass transport limitations / reactant starvation and protonic conductivity decrease, respectively. Cross sections of the membrane catalyst and gas diffusion layers examined by scanning electron microscopy indicate electrode thickness reduction as a result of ageing. Catalyst particles are found to migrate outwards and located on carbon backings. Nafion degradation in fuel cell environment is analysed in terms of the mechanism for fluoride release which is considered an early predictor of membrane degradation. The application of a full range of diagnostic techniques and modelling is felt necessary in order to aid design and operating strategies in PEM fuel cells.
- NaOH free hydrolysis of sodium borohydride for hydrogen productionPublication . Ferreira, M. J. F.; Gales, L.; Rangel, C. M.; Pinto, A. M. F. R.
- Hydrogen energy power system for a stand-alone weekend-home applicationPublication . Rangel, C. M.; Bozukov, Latchezar N.With an increase in renewable energies penetration and a market potential for the introduction of hydrogen into stand-alone energy systems, aspects related with the immaturity of some of the technologies which integrate the hydrogen sub-system, represent important unresolved technical issues, entailing unavailable components or availability at high costs. As a consequence, there is a growing initiative in the development and implementation of such a systems, that may demonstrate improved energy efficiency, response time, and safety in the storage option looking for an increase in the energy round-trip efficiency of the hydrogen subsystem. In this work, a novel demonstration of a Hydrogen Weekend Bungalow powered as a standalone renewable hydrogen energy system is presented. The main system components are: 1.25 kW PV Solar Panel with DC- hydrogen generator; 10 Nm3 Hydrogen Storage tank on the base of metal hydrides; Novel Hydrogen Cooker - 2 x 1000W and Hydrogen Refrigerator –power - 50W; Fuel Cell 500 – 1000 W with Converter - 48 V DC - 220 VAC, 1.5 kW ; Hydrogen and water control system. During the day, electricity from PV panels is collected and stored as hydrogen. The Fuel Cell is supplied from hydrogen from a vessel containing a metallic hydride storage solution. The hydrogen storage tank is able to supply a novel Hydrogen Kitchen and Fuel Cell with hydrogen for production of minimum 10 kWh electricity and/or 20 kWh thermal power in total. Hydrogen can be directly converted to thermal energy by hydrogen burners being of a simple, safe and sturdy construction and free COx and low NOx emissions. Hydrogen burners with a thermal power output from 500 to 5000 kW have been developed by Labtech, the equipment meets the UNIDO requirement for the development of a H2 cooker with portable hydride storage. It is considered an important solution for areas which have no grid and no effective energy carrier.
- Bio-Hydrogen production from glycerol by a strain of Enrerobacter aerogenesPublication . Marques, Paula; Bartolomeu, M. Lourdes; Tomé, M. Manuela; Neves, L. M.In this work, H2 production by a strain of Enterobacter aerogenes using as substrate pure glycerol and glycerol-containing biodiesel wastes was compared. The effect of physico-chemical parameters such as temperature, initial substrate and biomass concentrations on the bio-hydrogen production efficiency was investigated. The influence of the simultaneous removal of gases produced was also evaluated The results obtained showed that a decrease of the process temperature of 37 to 30 ºC leads to both, an increase of the bio-hydrogen production rate and a decrease of the equilibrium time of the process. Furthermore, it was also observed that using 10 g/dm3 of pure glycerol or biodiesel wastes containing the same concentration of glycerol as substrate lead to very similar bio-hydrogen production yields (2.5dm3 H2/dm3 fermentation medium). This proves that the performance of the strain of E. aerogenes used was not influenced by the presence of other components than glycerol in biodiesel residues, at least for the biodiesel wastes concentration studied. Simultaneous removal of gaseous phase (mainly H2 and CO2), with its production, shows to be very efficient leading to an increase of the value of the H2/CO2 volumetric ratio, in the headspace, from 2 to 8, which is very promising regarding costs involved in the technologies for purification of H2 produced.
- On the use of supercapacitors within stand-alone energy systemsPublication . Simões, João; Coelho, Miguel; Fernandes, Vitor; Rangel, C. M.; Martins, J. F.; Rodrigues, LeãoHydrogen is a valuable alternative for long-term energy storage, particularly for renewable energy based stand-alone systems. The described stand-alone system has been developed and installed at the INETI facilities. The exceeding renewable energy (provided by sun and wind) is used to generate hydrogen, which accumulated as an energy buffer, while the fuel cell uses this stored hydrogen to produce electrical energy when there is insufficient solar/wind energy. To provide the stand-alone system with a reliable energy storage it was designed a system for storing hydrogen based on metal hydrides. In order to supply sudden power demands two options were considered: a standard DC battery bank and a supercapacitor bank. Experimental and simulation results are presented in order to show the installation obtained performance.
- Water management in PEMFCPublication . Falcão, D. S.; Rangel, C. M.; Pinho, C.; Pinto, A.M.F.R.The potential of fuel cells for clean and efficient energy conversion is generally recognized. Proton-exchange membrane (PEM) Fuel Cells are among the different types of fuel cells one of the most promising. The water management is a critical problem to overcome in the PEM fuel cell technology. Despite several studies on this topic effective water management is still elusive. Models play an important role in fuel cell development since they enable the understanding of the influence of different parameters on the cell performance allowing a systematic simulation, design and optimization of fuel cells systems. In this work, a model previously developed and validated [1], is used to predict the water transport through the cell. The model takes into account heat and mass transport effects The influence of membrane thickness and transport properties, GDL thickness and structure, reactants pressure and humidification temperatures, on the water content through the membrane and on the cell performance was studied. All these parameters have an important impact in the cell water management. The model predicts the membrane water contents and water concentration profiles along the MEA. This work represents a useful tool to set-up suitable operating conditions and optimized tailored MEAs to produce a better performance of PEM fuel cells.
- A direct methanol fuel cell with low methanol crossover and high methanol concentrations :modelling and experimenal studiesPublication . Oliveira, V. B.; Rangel, C. M.; Pinto, A. M. F. R.The direct methanol fuel cell (DMFC) with proton exchange membrane (PEM) as electrolyte and liquid methanol/water as the energy carrier is a promising power source for micro and various portable electronic devices (mobile phones, PDA’s, laptops and multimedia equipment). However a number of issues need to be resolved before DMFC can be commercially viable such as the methanol crossover and water crossover which must be minimised in portable DMFC’s. In the present work, a detailed experimental study on the performance of an «in-house» developed DMFC with 25cm2 of active membrane area, working near ambient conditions (ambient temperature and pressure) is described. Tailored MEAS (membrane electrode assemblies), with different structures and combinations of gas diffusion layers (GDL), were designed and tested in order to select optimal working conditions at relatively high methanol concentration levels without sacrificing performance. The experimental polarization curves were successfully compared with the predictions of a steady state, one-dimensional model accounting for coupled heat and mass transfer, along with the electrochemical reactions occurring in the DMFC recently developed by the same authors. The influence of the anode gas diffusion layer media, the membrane thickness and the MEA properties on the cell performance is explained under the light of the predicted methanol crossover rate across the membrane
- LUCIS:a learning experience to improve lifetime and operating strategies in low power PEM fuel cellsPublication . Barbosa, R.; Travassos, Maria Antónia; Rangel, C. M.; Sá, R.; Silva, D.; Magalhães, A.; Ferreira, V.LUCIS, a demonstration project co-financed by the Innovation Agency in Portugal (AdI), was carried out in the framework of the DEMTEC Programme (Incentives to Technologically Innovative Pilot Systems). Its main goals were: Validate the reliability of proton exchange membrane fuel cells (PEMFC) when used in practical situations and the competitive advantages that these solutions can represent compared to conventional solutions; Evaluate impacts associated with the use of hydrogen and the benefits to business competitiveness. This project allowed a learning experience in real applications of low power PEMFC. Demonstrations were grouped in two large categories that covered several applications of PEMFC. The prototypes used were produced by SRE (Portugal) and were specifically designed to be used in small power applications, portable, traction or stationary. In this work, the technological validation was carried out for different stacks with power from 10 to 100W. Hydrogen was supplied by compressed gas bottles and metallic hydrides. All the fuel cells were previously characterized in specialized laboratories. Recommendations were drawn for every application in order to improve fuel cell lifetime and operating strategies.
- Hydrogen PEMFC stack performance analysis : a data-driven approachPublication . Lopes, Vitor V.; Novais, Augusto Q.; Rangel, C. M.For low power fuel cells, it is paramount that management of reactants, water and heat, be realized in a passive fashion in order to minimize parasitic losses. Effective fuel, oxygen supply and water management for reliable performance are also greatly affected by cell geometry and materials. Fuel cells are complex systems to optimize on a mere experimental basis. As an aid to this goal, data-driven analysis techniques, requiring no mathematical model to be fixed a priori, are gaining a reputation in other fields of work, where a phenomenological modeling approach might be intractable. This work presents a characterization study of a 12W PEMFC series stack by means of a new data-driven technique, M-NMF. The stack was developed for low temperature operation, uses own designed flow field plates, integrated in a series configuration, and is operated for 12 combinations of hydrogen/air flowrate ratios, generating as many polarization curves. M-NMF is applied, in combination with an alternating least squares algorithm, to the analysis of the overvoltage data matrix derived from the original experimental polarization data. From this analysis, it is possible to group and differentiate data according to similar overvoltage patterns and gain insight into their relative contribution to fuel cell performance immunization.