The electrolyte supported cells satisfy the requirements for the application in the solid oxide fuel cell such as mechanical stability, long-term stability during operation at temperatures <1000{degree sign}C, thermal cycling and very low degradation during repeated anode reduction/oxidation cycles. Nevertheless an enhancement of the power density at T=800-850{degree sign}C should be achieved to increase the power density level towards anode supported cells. The electrolyte supported solid oxide fuel cells on dense 8YSZ or 10Sc1CeSZ tapes (50x50x0.150 mm) with screen printed nickel oxide and yttria stabilized zirconia cermet anode (NiO/YSZ) and lanthanum strontium manganite and yttria stabilized zirconia composite cathode (uLSM/YSZ) were sintered in co-firing. The long-term tests (over 1000 hours) were carried out at 850{degree sign}C at constant load of 550 mA/cm2 (H2:H2O:N2=40:5:55, fuel utilization uf=50%) for 8YSZ based MEA and 650 mA/cm2 (H2:H2O=50:50, uf=23%) for 10Sc1CeSZ based MEA. During the redox cycle the cells were unloaded and fully oxidized by air for 120-180 min. Up to 10 redox cycles were performed. The field emission scanning electron microscopy (FESEM) was used to characterize the microstructural changes that occurred after long-term and redox cycles experiments. Changes of polarization resistance of the cells during the experiments were analyzed by impedance spectroscopy.
Nickel oxide and yttria-stabilized zirconia (NiO/YSZ) cermets have been prepared using a chemical co-precipitation of hydroxides. The influence of different factors on the microstructure, mechanical and electrochemical properties of the anode were investigated. The electrochemical tests were carried out on dense 8YSZ and 10Sc1CeSZ tapes (50x50x0.150 mm 3 , Kerafol GmbH) with symmetrically screen-printed cathodes and anodes with a lateral dimension of 40x40 mm. The cells were sintered in co-firing. The anodes were characterized by impedance spectroscopy at open circuit potential and under current load at temperatures of 850-950°C in hydrogen/steam atmosphere (H 2 :H 2 O = 1:1). The electrode polarization resistance (Rp) of the spectra was identified and the influences of operating temperature (850, 900 and 950°C), current load and pH 2 O on the impedance spectra of the anode were discussed. The long-term stability of the cell with an anode prepared by co-precipitation was carried out over 1000 hours under current density of 430-450 mA/cm 2 @ 0.7V at a temperature of 850°C.
The durability tests were carried out on substrate supported cells based on yttria and scandia stabilized zirconia(YSZ and ScSZ) with conventional A-site deficient lanthanum strontium manganite(uLSM)/YSZ and Ni/YSZ electrodes. The cells were operated at 850°C in air/H 2 :H 2 O (1:1) for more than 1000 h at current densities >450 mA/cm 2 . The reduction of the cathode polarization resistance is observed from the analysis of the impedance spectra. Microstructure investigations of the composite cathode using FESEM and TEM revealed that the composite cathode undergoes morphology changes during the first 200-500h of the operation creating some nano-porosity at the uLSM/YSZ interface. Furthermore it was found that the change of the microstructure is strongly affected by the magnitude of the current density. The depth of the electrochemically structured zone as well as the change of the uLSM-composition at the uLSM/YSZinterface was investigated using transmission electron microscopy.
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