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- PEM Fuel Cells: materials ageing and degradationPublication . Silva, R. A.; Paiva Luís, Teresa; Rangel, C. M.As fuel cell technology matures and time scale to commercialization decreases, the need for a more comprehensive knowledge of materials ageing mechanisms is essential to attain specified lifetime requirements for applications. In this work, the membrane-electrode assembly (MEA) degradation of an eight cell PEM low power stack was evaluated, during and after fuel cell ageing in extreme testing conditions. The stack degradation analysis comprised observation of catalytic layer, morphology and composition. Cross sections examination of the MEAs revealed thickness variation of catalytic layer and membrane. Other modes of degradation such as cracking,
- MEA degradation in PEM Fuel Cell : a joint SEM and TEM studyPublication . Silva, R. A.; Hashimoto, T.; Thompson, G. E.; Rangel, C. M.One of the important factors determining the lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is membrane electrode assembly (MEA) degradation and failure. The lack of effective mitigation methods is largely due to the currently very limited understanding of the underlying mechanisms for mechanical and chemical degradations of fuel cell MEAs. This work reports on the effect of 1500 h operation of an eight-cell stack Portuguese prototype low power fuel cell. A performance decrease of 34%, in terms of maximum power, was found at the end of testing period. A post-mortem analysis by SEM and TEM was done for most cells of the fuel cell. Loss of the PTFE ionomer in the anode and cathode catalytic layers; morphological changes in the catalyst surfaces such as loss of porosity and platinum aggregation, deformation on the MEA components (anode, cathode and membrane) were identified. Others, like delamination and cracking were also detected. Catalyst migration and agglomeration on the interface of the electrodes was observed at cells 2, 4, 6 and 7. A platinum band was also detected on the membrane at 2 μm apart from the anode of cell 4. In some cases, dissolution occurred with re-deposition of the platinum particles with facet
- New proton conductive membranes of indazole- and condensed pyrazolebisphosphonic acid-Nafion membranes for PEMFCPublication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.ABSTRACT: The global demands of energy are still increasing alongside many civilizational problems, notably the effects on the environment due to the overuse of traditional energy sources based on fossil fuels. New cleaner, renewable sources for sustainable energy systems are a key challenge of the 21st century society.
- A power management strategy for a stand-alone photovoltaic/fuel cell energy system for a 1kW applicationPublication . Pinto, P.J.R.; Rangel, C. M.In this paper a power management strategy is presented for a stand-alone photovoltaic (PV)/fuel cell (FC) energy system. PV is the primary power source of the system and an FC-electrolyzer combination is used as a backup and a long-term storage system. The energy in the hybrid system is balanced by the common dc bus voltage regulation. A simple hysteresis voltage control is used for dc bus voltage regulation. In this way, the fuel cell and the electrolyzer can be protected from unnecessary utilization or irregular operation (reduction of frequent start-ups and shutdowns). Simulation results obtained using Matlab and Simulink are presented to verify the effectiveness of the proposed control algorithm.
- Gold deposition from 1-butyl-1-methyl-pyrrolidinium dicyanamide ionic liquid at open-circuit and under potentiostatic controlPublication . Sá, A.I. De; Eugénio, S.; Quaresma, S.; Rangel, C. M.; Vilar, R.In this work, the deposition of gold on copper substrates from solutions of HAuCl4.3H2O in 1-butyl-1-methylpyrrolidinium dicyanamide was studied. Deposition was carried out in open-circuit and under potentiostatic control at temperatures from 293 to 353 K, in normal atmosphere, with deposition conditions allowing water from atmospheric absorption up to 0.8 wt.%. Films of gold were obtained by both methods. Deposition at open-circuit occurs by galvanic displacement mechanism. Involvement of Cu+ species in the electrodeposition process was suggested by cyclic voltammetry. Furthermore, copper incorporation in the gold films was confirmed by X-ray diffraction. SEM observation and XRD analysis show that films are nanocrystalline with a globular morphology except for the films formed under potentiostatic control at 353 K, which show a dendritic structure. The size of the crystallites determined by Scherrer's equation varies in the range from 6 to 25 nm.
- Characterisation and performance studies of a LiFePO4 cathode material synthesized by microwave heatingPublication . Plancha, Maria João; Paiva Luís, Teresa; Rangel, C. M.Lithium iron phosphate with incorporated carbon, LiFePO4-C, was synthesized by the microwave-assisted method. X-ray diffraction analyses showed higher crystallization degrees for samples submitted to higher irradiation times. A particle-agglomerated morphology was associated as revealed by scanning electron microscopy. The electrochemical character-istics of a composite cathode containing the synthesized product were evaluated. The two-phase electrochemical process between FePO4 and LiFePO4 was evidenced in the cycling voltammogram profile and its reversibility and stability were demonstrated. An additional redox reversible reaction was revealed and assigned to another phosphate present in the synthesized product. The charge/discharge performance study indicated a good capacity retention after the initial cy-cles where capacity fading was associated to the resistance of a SEI film that forms and grows on the cathode’s surface. Results obtained by electrochemical impedance analysis before and after cell’s cycling are discussed.
- Aerogel cathodes for electrochemical CO2 reduction [Comunicação oral]Publication . Messias, Sofia; Fialho, Maria T.; Paninho, A. B.; Branco, Luis C; Nunes, A. V. M.; Martins, Rodrigo; Mendes, Manuel Joao; Nunes, D.; Rangel, C. M.; Machado, AnaABSTRACT: Electrochemical reduction of carbon dioxide powered by renewable energy to produce fuels and chemicals is a technology with potential to contribute to an economy based on a carbon neutral cycle. The development of cost effective, highly active and stable catalysts for CO2 electroreduction is being intensively researched. This work addresses the development of aerogel supported copper-zinc bimetallic catalysts[1]. Aerogels are substances with exceptional properties with many current and potential applications [2-3]. Due to their high surface area, stability in corresponding gaseous or liquid phases, transport through large meso and macropores they are especially suited as catalysts and carrier materials for catalysis and, when electric conductive for electro-catalysis. Aerogels prepared by the sol gel method and impregnated with metallic particles will be tested as cathodes for the co-electrolysis of CO2 and water to produce syngas at temperatures near room temperature and high-pressure. In this way this process can be directly coupled to other high pressure processes, such as Fischer-Tropsch that use high pressure syngas as raw material. Productivities and faradaic efficiencies will be evaluated. The characterization of the aerogel-based cathodes will be undertaken by surface analysis techniques. BET surface areas will be determined. The catalytic cathodes will be tested in an ionic liquid-based electrolyte as a way to increase current densities, due to the high CO2 solubilities exhibited by some ionic liquid families.
- Simulation of a stand-alone residential PEMFC power system with sodium borohydride as hydrogen sourcePublication . Pinto, P.J.R.; Sousa, T.; Fernandes, Vitor; Pinto, A. M. F. R.; Rangel, C. M.Catalytic hydrolysis of sodium borohydride (NaBH4) has been investigated as a method to generate hydrogen for fuel cell applications. The high purity of the generated hydrogen makes this process a potential source of hydrogen for polymer electrolyte membrane fuel cells (PEMFCs). In this paper, a PEMFC power system employing a NaBH4 hydrogen generator is designed to supply continuous power to residential power applications as stand-alone loads and simulated using Matlab/Simulink software package. The overall system is sized to meet a real end-use load, representative of standard European domestic medium electric energy consumption, over a 1-week period. Supervisory control strategies are proposed to manage the hydrogen generation and storage, and the power flow. Simulation results show that the proposed supervisory control strategies are effective and the NaBH4–PEMFC power system is a technologically feasible solution for stand-alone residential applications.
- Novel data-driven methodologies for parameter estimation and interpretation of fuel cells performancePublication . Lopes, Vitor V.; Novais, Augusto Q.; Rangel, C. M.Fuel cell based power generation systems are expected to become more widespread in the near future. Stationary fuel cells may be used as an uninterruptible or back-up power supply, or to supply micro-grids. In particular, proton exchange membrane fuel cells (PEMFC) are an attractive technology due to its high energy density, rigid and simple structure, low operating temperature and fast start-up characteristics. The power quality assessment of fuel cells as a viable power sources requires a good understanding of the fuel cell performance characteristics. This paper presents two novel data-driven methodologies for the identification of the main steady state (polarization curve) and the dynamic (impedance response) characteristics for fuel-cells allowing the development of rapid, accurate and empirical models based on the experimental data. M-NMF is a modified non-negative matrix factorization technique developed for the analysis of polarization curve data that allows to identify the three main contributions for the fuel-cell power degradation, while for impedance spectroscopy data, this paper proposes the use of fractional order transfer functions (FC-FOTC) to describe the main dynamic modes present in the fuel-cell. A brief description of these two approaches is presented, together with the analysis of a real experimental dataset obtained from a 12W open cathode PEMFC stack to illustrate their potential and scope. While the former is instrumental for the deconvolution of the fuel cell polarization curves into its major components, the latter enables the estimation of the parameters related to the inherent transport and kinetic phenomena, thus opening the way, in both cases, for the interpretation of the effect of the operating conditions on the relative dominance and magnitude of these components and phenomena.
- Atlas Nacional do H2 Verde SustentávelPublication . Ponce Leao, Maria Teresa; Simoes, Sofia; Simões, Teresa; Quental, Lídia; Catarino, Justina; Amorim, Filipa; Brás, Teresa; Patinha, Pedro; Lopes, Tiago; Rodrigues, Carlos; Machado, Susana; Rangel, C. M.; Gírio, Francisco; Picado, AnaRESUMO: O "Atlas Nacional do H2 Verde Sustentável" tem como objetivo apoiar o processo de decisão quanto à localização de projetos de produção de hidrogénio verde no território de Portugal continental. O Atlas foi desenvolvido pelo LNEG em colaboração com várias entidades públicas e privadas nacionais. De uma forma mais geral, apoia à a transição para um país neutro em carbono, desenvolvendo uma economia de baixo carbono, liderando em inovação e desenvolvimento tecnológico.