Electrochemical and microstructural studies of Ni-YSZ anode redox behaviour

A new approach for in-situ conductivity measurements of the Ni phase in Ni/YSZ cermet anode during its formation and redox cycling, applying impedance spectroscopy, is introduced. The electrochemical testing is combined with direct gases (H2, N2 and their mixtures) permeability measurements. The resistance of the samples, which has inductive behavior, reaches ? constant value of about 40 mΩ in the first 10-15 minutes and does not change during further reduction. The resistance decreases with about 8-10% after the first oxidation-reduction cycle. In the next cycles it does not change, or slightly increases. The permeability of the redox cycled samples is lower. Although there is a general correlation between permeability and porosity, depending on the testing conditions, for samples with the same porosity, the permeability differs due to different tortuosity.