-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Journal of Applied Electrochemistry 01/2002; 32(8):929-936. · 1.75 Impact Factor
-
Journal of Power Sources 01/2002; 106(1-2):196-205. · 4.95 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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=0.30–0.40) in a eutectic melt (Li:K) at 650 °C 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=0.30, for which a reduction of the particle size was observed. NiO presented an important morphological change due to its lithiation in situ.
Journal of Power Sources 118:23-34. · 4.95 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The molten carbonate fuel cell (MCFC) is expected to be an efficient device for the conversion of chemical energy in the near future. However, one of the major limits to the lifetime is the dissolution of the nickel oxide cathode in the electrolyte. This problem can be overcome by the addition of new compounds to the nickel oxide. In this way, the performance and the endurance of a new Ni–Ce cathode for MCFC has been tested and the results compared to a commercial nickel cathode. The polarisation curves were measured in order to check the degradation of the cell performance with time. The results showed a better performance with the novel cathode material (136 mW/cm2 at 200 mA/cm2 during 2100 h) than the commercial one (the voltage decreased from 120 to 108 mW/cm2 at 150 mA/cm2 in 1000 h). The better performance of Ni–Ce cathode with respect to the Ni one can be attributed to the good effect of cerium in the cathode. The change in the nickel crystalline structure reduces the dissolution of nickel in the electrolyte and implies a greater endurance of the cell. The current–voltage curves were measured and showed the same trend for both cells. Postmortem analyses were done in order to characterise the cells. As a conclusion, the addition of cerium can be beneficial to overcome the dissolution of the nickel cathode in the electrolyte, which is considered one of the major limits to the lifetime of a MCFC.
Journal of Power Sources 106:189-195. · 4.95 Impact Factor
-
[show abstract]
[hide abstract]
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.
Journal of Power Sources.
-
[show abstract]
[hide abstract]
ABSTRACT: Porous nickel cathode was protected by potentiostatically deposited cobalt at different experimental conditions: oxidation potential and electrolysis duration. The deposition growth increased with the oxidation potential yielding a more developed granular structure with smaller grains. Thin layers of Co3O4 were identified by X-ray diffraction (XRD) and Raman spectroscopy. CoOOH was detected by X-ray photoelectron spectroscopy (XPS) before annealing treatment and Co3O4 after heating the sample at 500 °C during 4 h in air. After this treatment, some morphological changes were observed on the coated samples due to grain compaction and oxidation of the nickel substrate. The porosity of the coated samples was relatively close to that of the sole porous nickel. These coatings exhibited an appropriate dual-pore structure with macro and micro pores, a basic MCFC requirement.
Journal of Power Sources.
