Probe electrode study of cathodically polarized PtIr-YSZ interfaces

Local cathodic polarizations of yttria-stabilized zirconia were carried out with a PtIr probe as the working electrode in a controlled atmosphere high temperature scanning probe microscope to investigate the reduction of zirconia. Impedance spectroscopy was performed at 650 °C during increasing and decreasing polarization, in a range between 0.5 V and −2 V in 9% H2 in N2 saturated with water vapor at room temperature (25 oC).

With increased polarization, the impedance spectra changed from a simple suppressed arc at low polarizations into two capacitive arcs separated by an inductive loop and followed by an inductive loop at low frequencies. Areas with high conductance as well as significantly decreased high frequency resistances resulted from the polarizations and indicate the introduction of electronic conductivity in YSZ.

Near the probe|YSZ contacts, areas with very low conductance and accumulation of Si-containing particles were observed, pointing to additional migration of silica impurities towards the probe.