The Reduction Process of a NiO/YSZ Anode for Intermediate Temperature Solid Oxide Fuel Cells

The reduction behavior of a sintered NiO/YSZ anode used for intermediate temperature solid oxide fuel cells was studied by hydrogen temperature-programmed reduction (H-2-TPR). The reduction process of the NiO/YSZ anode in the cell was in situ monitored by open circuit voltage (OCV) and electrochemical impedance spectroscopy (EIS). H-2-TPR results show that the higher sintering temperature of the NiO/YSZ anode results in a slower reduction of NiO to metallic Ni. However, when the sintering temperature is elevated to 1500 degrees C, the reduction of sintered NiO/YSZ anode powder instead becomes easier. The higher NiO content in the anode leads to the more rapid reduction of the corresponding anode powder. The above H2-TPR results can be attributed to the combined effects of the growth up of NiO particles and the interface separation between NiO and YSZ caused by the anode sintering. The variation of OCVs reveals that for the cells, the anode with higher NiO content has a slower reduction process, which can be ascribed to the retarding effect of excessive H2O produced during the initial reduction period. It was found from the EIS results that the 50% NiO/YSZ anode has a most stable reduction process, whereas for the cells with 30 % and 70 % NiO/YSZ anodes, both the polarization resistances gradually increase after experiencing an initial decrease for a short period. The cell polarization resistance with 30 % NiO/YSZ anode keeps no change any more after reduction for 600 min, whereas the cell polarization resistance with 70 % NiO/YSZ anode increases continuously

La0.4Ce0.6O1.8-La0.8Sr0.2MnO3-8 mol% yttria-stabilized zirconia composite cathode for anode-supported solid oxide fuel cells

The composite cathodes of La0.4Ce0.6O1.8 (LDC)-La0.8Sr0.2MnO3 (LSM)-8 mol% yttria-stabilized zirconia (YSZ) with different LDC contents were investigated for anode-supported solid oxide fuel cells with thin film YSZ electrolyte. The oxygen temperature-programmed desorption profiles of the LDC-LSM-YSZ composites indicate that the addition of LDC increases surface oxygen vacancies. The cell performance was improved largely after the addition of LDC, and the best cell performance was achieved on the cells with the composite cathodes containing 10 wt% or 15 wt% LDC. The electrode polarization resistance was reduced significantly after the addition of LDC. At 800 degrees C and 650 degrees C, the polarization resistances of the cell with a 10 wt% LDC composite cathode are 70% and 40% of those of the cell with a LSM-YSZ composite cathode, respectively. The impedance spectra show that the processes associated with the dissociative adsorption of oxygen and diffusion of oxygen intermediates and/or oxygen ions on LSM surface and transfer of oxygen species at triple phase boundaries are accelerated after the addition of LDC. (C) 2007 Elsevier B.V. All rights reserved

Interaction of La(0.8)Sr(0.2)MnO(3) interlayer with Gd(0.1)Ce(0.9)O(1.95) electrolyte membrane and Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-delta) cathode in low-temperature solid oxide fuel cells

Low-temperature solid oxide fuel cells with a La(0.8)Sr(0.2)MnO(3) (LSM) interlayer between the Ce(0.9)Gd(0.1)O(1.95) (GDC) electrolyte membrane (20 mu m) and the Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3) (BSCF)-GDC composite cathode are fabricated by sintering the BSCF-GDC composite cathodes at 900,950 and 1000 degrees C. The results of scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) fora model LSM/BSCF bi-layer pellet suggest that Ba, Co and Fe in BSCF as well as La and Mn in LSM have diffused into their counter sides. The X-ray diffraction (XRD) results on the simulated cells also indicate the incorporation of La into the CDC electrolyte membrane and the mutual diffusion of elements between the LSM layer and the BSCF layer. Analysis of the impedance spectra and interfacial reaction activation energies shows that LSM interlayer accelerates the oxygen reduction. Considering a good cell performance and the highest open-circuit voltages (OCVs) at 600-500 degrees C, the optimum sintering temperature of BSCF-GDC composite cathode onto LSM interlayer is 900 degrees C. (C) 2008 Elsevier B.V. All rights reserved