Reduction kinetics of undoped and aluminum titanate (Al2TiO5) doped NiO-YSZ solid oxide fuel cell anodes

Undoped and 1-10 wt% aluminum titanate, Al2TiO5, (ALT) doped nickel oxide/yttria-stabilized zirconia (NiO/YSZ) anode materials were kinetically evaluated during isothermal (800 °C) H2 reduction (5% H2-95% N2 and pure H2 gas). It was found that the two parameter Avrami-Erofe'ev model (AEn) was the most successful in representing reduction kinetics. The reduction mechanisms have been identified as the formation and growth of nuclei and is maintained after aluminum titanate, Al2TiO5, (ALT) doping and when the H2 concentration in the gas flow is increased. ALT doped samples result in the formation of NiAl2O4; which, when present in sufficient amounts, slowly reduces causing a shift of the model from the experimental data. This phenomenon has been correlated, through microstructural evaluation, to the formation of Ni nanoparticles. In all investigated cases, the reduction kinetics of the system was accelerated when the H2 concentration was increased from 5% to 100%.