Electrode polarization at the Au, O2 (g) / yttria stabilized zirconia interface. Part II: electrochemical measurements and analysis

Abstract

The impedance of the Au,O,(g)/yttria stabilized zirconia interface has been measured as function of the overpotential, temperature and oxygen partial pressure. At large cathodic overpotentials (vi -0. I V) and large anodic overpotentials (7~ +O. I V) inductive effects are observed in the impedance diagram at low frequencies. Those inductive effects result from a charge transfer mechanism where a stepwise transfer of electrons towards adsorbed oxygen species occurs. A model analysis shows that the inductive effects at cathodic overpotentials appear when the fraction of coverage of one of the intermediates increases with more negative cathodic overpotentials.The steady state current-voltage characteristics can be analyzed with a Butler-Volmer type of equation. The apparent cathodic charge transfer coefficient is close to 01, =0.5 and the apparent anodic charge transfer coefficient varies between I .7 < (Y, -C 2.8. The logarithm of the equilibrium exchange current density ( lo ) shows a positive dependence on the logarithm ofthe oxygen partial pressure with a slope of m = (0.602 0.02). Both the apparent cathodic charge transfer coefficient and the oxygen partial pressure dependence of I,, are in accordance with a reaction model where a competition exists between charge transfer and mass transport of molecular adsorbed oxygen species along the electrode/solid electrolyte interface. The apparent anodic charge transfer coefficients deviate from the model prediction.

Oxygen transfer properties of ion-implanted yttria-stabilized zirconia

“…Also Re, for the Fe-YSZ has a (Po2)" dependence with m=0.25 while for the normal YSZ m varies from 0.53 (0.01 >Po_~ > 1 atm) to below 0.25 for Po2 below l0 -4 atm [ 13]. For both systems a similar exponential dependence on t/ is observed for Re, related to the anodic and cathodic charge transfer coefficients, eq.…”

“…By implanting Fe at 50 keV (also at a dose of 8× 10 ~6 atoms cm -2) a buried layer is obtained. For these samples the conductivities measured in N 2 and in H 2 were both virtually identical of polarization (bias) using a standard three-electrode arrangement [3,13]. As platinum possesses a high activity for dissociative adsorption of oxygen, Pt electrodes can have a significant influence on the electrode reaction rate.…”

“…For both systems a similar exponential dependence on t/ is observed for Re, related to the anodic and cathodic charge transfer coefficients, eq. (3) [ 13,17 ].…”

Impedance Analysis of Electrochemical NOx Sensor Using a Au/Yttria-Stabilized Zirconia (YSZ)/Au cell

“…The calculated capacitance exhibits only a slight dependence on temperature or O 2 , in all cases ranging between 0.32 and 0.37 µF. However, general trends indicate that capacitance increases with P O 2 , which may be related to an increase in the fraction of adsorbed O 2 species at the Au/YSZ interface [11,13].…”

“…Since R S is insensitive to O 2 , average values at all O 2 concentrations are shown resulting in an E a of 93 kJ/mol, which is consistent with ionic diffusion in YSZ. An E a of 89 kJ/mole has been reported in a Au, O 2 (g)/YSZ system [11]. Hertz, et al, found differing E a for gold (88 kJ/mol) and platinum (74 kJ/mol) electrodes on thin film YSZ [12].…”