Microstructure stability studies of Ni patterned anodes for SOFC

Although fundamental work has focused for a while now on the kinetics of the Ni–YSZ cermet anode, there still is no consensus on the rate determining steps. Due to their two-dimensional geometry, Ni patterned anodes allow to examine the electrochemistry at the triple phase boundary. Results of previous studies with Ni patterned anodes report different ranges for the line specific resistance (LSR) and controversial behaviors upon parameter variation of partial pressure of H2 and H2O as well as temperature. Hence, a consistent data set for modelling studies of the kinetic processes does not exist. To obtain accurate data, edge quality and Ni layer stability under thermal exposure are essential parameters. Therefore, in the present contribution, the influence of the layer thickness, temperature and gas composition on the stability of Ni thin films is examined in detail. Conclusions on limitations for parameter variation under stable operation parameters are drawn; the importance of an initial heat treatment is demonstrated and an additional correction factor for the inevitable increase in triple phase boundary length during characterization at elevated temperatures (T = 800 °C) is introduced.