INFLUENCE OF CURRENT DENSITY AND FUEL UTILIZATION ON THE DEGRADATION OF THE ANODE

To investigate the efficiency and long term stability of Ni-YSZ-cermet anodes as a function of current density and fuel utilization, various SOFC single cells were operated under realistic working conditions for approximately 700h. The gas composition present at different positions in a fuel cell stack, because of the fuel utilization of the preceding cells, was simulated by adding a well known amount of oxygen to the fuel (H2). After operation the microstructure of the anodes was analyzed with optical microscopy and SEM. The nickel distribution before and after operation was investigated by EDX and TEM. Nickel diffusion into the electrolyte was studied by WDX. These investigations showed possible degradation processes occurring in a Ni-YSZ-cermet anode and indicated the limits of current density and fuel utilization, within which a degradation of the anode may be tolerated.