Degradation and Relaxation Effects of Ni Patterned Anodes in H-2-H2O Atmosphere

Patterned Ni anodes on Y2O3-stabilized ZrO2 (YSZ) represent a promising approach to determine the kinetics of electrochemical reactions in solid oxide fuel cells. Contrary to technical Ni/YSZ cermet anodes, the reaction zone for the hydrogen oxidation has the potential to be well defined. This study is focused on the reproducibility of electrochemical characterization results of patterned Ni anodes, with a parameter variation of the partial pressures of H-2 and H2O, temperature, and polarization voltage. Considerable (electro)chemical relaxation and degradation processes with time constants in the order of some hours were found and are discussed: (i) an initial decrease in the line specific resistance (LSR) during the first 20-25 h of temperature exposure (T = 800 degrees C) attributed to a restructuring process in the Ni thin film, (ii) reversible changes in LSR upon variations of the partial pressure of H-2 and H2O in correlation to the initial gas composition, and (iii) rapid reversible changes in LSR upon anodic and cathodic polarization voltages followed by a slow relaxation. The corresponding preconditions for reliable measurement series were deduced and yield the data set of the LSR values. Furthermore, a detailed comparison of the obtained LSR values with literature data is given. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3383041] All rights reserved.