Performance and long term stability of large area anode supported solid oxide fuel cells (SOFCs)

A long term stability test was conducted on a large area anode supported cell. The cell consisted of anode support, NiO (Nickel Oxide) + YSZ (Yttira Stabilized Zirconia); an anode functional layer, NiO + YSZ; electrolyte, YSZ; a cathode functional layer, LSCF (La0.6Sr0.4Co0.2Fe0.8O3-d) + GDC (Gd doped ceria); and a cathode current collector, LSCF. For a single cell stack test set-up, FeCr alloy end plates were machined for a co-flow of fuel and oxidant gases through internal manifolds and gas channels. The cell voltage was measured in a constant current mode (0.4A/cm2) for ~ 4400 h at 750 °C. During the long term test, I–V curve and impedance spectra were frequently measured to trace an increase in ohmic and non-ohmic resistance as a function of time. It was found that the dominant factor in the single cell stack degradation was an increase of non-ohmic resistance (activation polarization) rather than ohmic resistance. After the long term test, a post-material analysis was conducted by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning Auger microscopy (SAM), energy dispersive spectroscopy (EDS), etc. The main degradation mechanism was determined to be the change of anode microstructure, which was caused by the high pressure of water vapor, especially at the gas outlet region.