Morphological changes at the interface of the nickel-yttria stabilized zirconia point electrode

The H2-H2O, Ni/YSZ point electrode was investigated using long-term potential step measurements and impedance spectroscopy at 1273 K. Morphological and structural changes at the electrode interface were evaluated by electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy ex situ. The anodic current was found to induce a self-catalytic effect on the electrode, and the anodic "steady state" current increased to more than twice the initial value with a time constant of about 40 h. In contrast, cathodic polarisation reduce the performance of the electrode, and the cathodic current decreased significantly with a time constant of about 20 h. In addition to morphological modifications, the catalytic properties of the surfaces were significantly altered as the electrode was polarised. Transformation from cubic to tetragonal YSZ, due to segregation of the material, was observed on the surface of the electrolyte when the sample was kept at working conditions for long periods of time. The passage of current was not found to generate any permanent phase transformation in the YSZ. 21 refs.