Electrochemical impedance investigation of the redox behaviour of a Ni–YSZ anode

The reoxidation and reduction of a Ni–YSZ anode were investigated by monitoring the variation of ohmic resistance and the open circuit voltage of anode supported cells using electrochemical impedance spectroscopy. The ohmic resistance curves showed that anode reoxidation could be largely divided into three stages: an initial stage with a slow increase of ohmic resistance, a quick oxidation stage with a sharp increase in ohmic resistance and a final stage with a slight decrease of ohmic resistance. Reoxidation at 800 °C was a rapid process with a short initial stage, whereas reoxidation at 500 °C did not proceed in the last two stages. The OCV curves showed that reoxidation above 600 °C caused cracking of the YSZ electrolyte film.