M.J. Escudero

Optimisation of flow-field in polymer electrolyte membrane fuel cells using computational fluid dynamics techniques

Abstract The purpose of this work was the enhancement of performance of Polymer Electrolyte Membrane Fuel Cells (PEMFC) by optimising the gas flow distribution system. To achieve this, 3D numerical simulations of the gas flow in the assembly, consisting of the fuel side of the bipolar plate and the anode, were performed using a commercial Computational Fluid Dynamics (CFD) software, the “FLUENT” package. Two types of flow distributors were investigated: a grooved plate with parallel channels of the type commonly used in commercial fuel cells, and a porous material. The simulation showed that the permeability of the gas flow distributor is a key parameter affecting the consumption of reactant gas in the electrodes. Fuel utilisation increased when decreasing the permeability of the flow distributor. In particular, fuel consumption increased significantly when the permeability of the porous material decreased to values below that of the anode. This effect was not observed in the grooved plate, which permeability was higher than that of the anode. Even though the permeability of the grooved plate can be diminished by reducing the width of the channels, values lower than 1 mm are difficult to attain in practice. The simulation shows that porous materials are more advantageous than grooved plates in terms of reactant gas utilisation.

Development and performance characterisation of new electrocatalysts for PEMFC

New electrocatalysts based on Pt, Pt-Ru and Pt-Pd have been prepared by the microemulsion method. This method allows the production of a very narrow size distribution of metal particles, with an av ...

Electrochemical behaviour of lithium–nickel oxides in molten carbonate

Impedance spectroscopy was used to investigate the stability and the catalytic activity of the lithium–nickel mixed oxides with high lithium content (LixNi1� xO, x ¼ 0:30–0.40) in a eutectic melt (Li:K) at 650 8C under a corrosive atmosphere (CO2:O2 4:1). The results were compared with a NiO reference cathode material. A modified transmission line model allowed to give a physical-meaning to the impedance spectra. All Li–Ni oxides showed similar catalytic activity and their impedance values were one order of magnitude lower than NiO. During the first 100 h of immersion, the samples showed structural changes due to the loss of lithium. Later on, the structure kept stable. The loss of lithium was confirmed by chemical analysis and X-ray diffraction (XRD). All Li–Ni oxide samples reduced the nickel dissolution in the eutectic in one order of magnitude in relation to NiO. In general, similar morphology was observed by scanning electron microscopy (SEM) for the fresh samples. After their immersion, the Li–Ni oxides did not show morphological change except for the sample with x ¼ 0:30, for which a reduction of the particle size was observed. NiO presented an important morphological change due to its lithiation in situ. # 2003 Elsevier Science B.V. All rights reserved.

Study of a Li-Ni oxide mixture as a novel cathode for molten carbonate fuel cells by electrochemical impedance spectroscopy

Li–Ni oxide mixtures with high lithium content are considered to be an alternative cathode material for molten carbonate fuel cells (MCFCs). The electrochemical behaviour of Li0.4Ni0.6O samples has been investigated in a Li–K carbonate melt at 650 °C by electrochemical impedance spectroscopy as a function of immersion time and O2 and CO2 partial pressure. The impedance spectra have been interpreted using a transmission line model that includes contact impedance between reactive particles. The Li0.4Ni0.6O powder particles show structural changes due to high lithium leakage and low nickel dissolution from the reactive surface to the electrolyte during the first 100 h of immersion. After this time, the structure seems to be stable. The partial pressures of O2 and CO2 affect the processes of oxygen reduction and Li–Ni oxide oxidation. X-ray diffraction and chemical analysis performed on samples before and after the electrochemical tests have confirmed that the lithium content decreases. SEM observations reveal a reduction in grain size after the electrochemical tests.

Testing an isolated system powered by solar energy and PEM fuel cell with hydrogen generation

Abstract Photovoltaic systems are widely used to power telecommunications systems in remote locations, but this is restricted by the irregular availability of solar energy. A European collaboration is developing and testing an autonomous system that combines a photovoltaic power system in combination with an electrolyzer that uses surplus power to produce hydrogen, which can be used in a PEM fuel cell when there is insufficient solar energy.