Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 2: Oxidation of zirconia

Abstract

The objective of the present paper is to review the literature on the mechanism and kinetics of oxidation of yttria-stabilised zirconia (YSZ) and related models of the transfer of charge and mass at the oxygen/zirconia interface at elevated temperatures. There is general agreement that oxygen may be incorporated efficiently into the lattice of zirconia at the triphase boundary (TPB), which is formed by the gas phase, zirconia oxygen ion conductor and electronic conductor. Thus, a number of efforts have been made to understand the effect of the TPB structure on the oxidation mechanism. Although it is clear that the TPB is required for efficient charge transfer at high current, there is a growing number of reports to the effect that oxygen may be incorporated into zirconia in the absence of the TPB. As a result, attempts have been made to develop zirconia for use in electrodeless zirconia-based electrochemical devices.

Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 8: Effect of temperature

“…1,2 Although it is clear that the presence of an electronic conductor results in enhancement of charge transfer at the oxygen/zirconia interface, there is no experimental evidence supporting the common assumption that oxygen incorporation into the lattice of zirconia in the absence of an electronic conductor cannot take place.…”

Feasibility of a Stack Integrated SOFC Optical Chemical Sensor

“…Figure 11 displays the peak position for various concentrations of H 2 as a function of O 2 concentration for the data seen in Figure 10-A. A dashed line connecting the data points for each H 2 concentration has been added to guide the eye along each data set, all of which exhibit a negative power dependence, which is expected from equation (9). A random SPR band peak position baseline shift is experienced from experiment to experiment, as mentioned previously, so averaging the peak position data from experiment to experiment results in a rather large standard deviation compared to the relative scale from data point to data point, even though the data follows the same gas concentration dependence for every experiment.…”

“…, as indicated in equation (9), which is plotted in Figure 13 for all four collected data sets. Plotted on the secondary ordinate is the calculated number of conduction electrons per nanoparticle based on the peak position using the electrostatic relation between peak position and number of conduction electrons (1).…”

“…, which can then be taken up by the vacancies in the YSZ matrix. 9 We propose that an increase in the O -species surface coverage at elevated surface temperatures may be causing the reduction in the NO 2 sensing signal for the same reason one would expect it to reduce the uptake of oxygen by YSZ. As demonstrated by the change in the SPR peak position and FWHM observed upon exposure to NO 2 , it is proposed that exposure to NO 2 results in an uptake of O 2-by the YSZ matrix and if NO 2 must first dissociate at the Au-YSZ surface into gas phase NO and chemisorbed O -then a reduction in surface area available for NO 2 to react, should result in a reduction in the measured signal change.…”

Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 12: Summary

“…1,2 There has been an accumulation of experimental data indicating that rather than the bulk phase, it is interfaces, such as grain boundaries and external surfaces, that control the performance of zirconia based electrochemical devices. 2 The influence of interfaces on the performance of zirconia may be considered in terms of the specific role of interfaces in charge transfer during the operation of electrochemical devices. The most notable interfacial effects which have an impact on the reactivity of zirconia include: (1) segregation of impurities, such as Si and Ca, to interfaces, such as grain boundaries.…”