DOUBLE-LAYER CAPACITANCE OF POROUS PLATINUM-ELECTRODES IN ZIRCONIA ELECTROCHEMICAL-CELLS

The capacitance of the double layer at the interface between porous platinum electrodes and yttria-stabilized zirconia has been measured by potential step chronoamperometry. The capacitance is independent of oxygen partial pressure and electrode potential and increases from 0.2-mu-F/cm2 at 555-degrees-C to 1.3-mu-F/cm2 at 695-degrees-C. These values are at least an order of magnitude smaller than capacitances extracted from the low-frequency portion of ac impedance spectra. This indicates that the capacitive behavior of platinum electrodes in zirconia cells is dominated by time-dependent faradaic processes.