Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 5: Reactivity models

Measurements of work function using the Kelvin method are based on determination of the contact potential difference (CPD) between the studied specimen and a reference electrode, typically Pt. The present work considers the physical meaning of the CPD, which is formed between the surfaces of a metal oxide and Pt in the presence of oxygen at elevated temperatures. The focus is on the reactivity of both metal oxide and Pt with oxygen and the associated electrical effects. The reactivity at the oxygen/zirconia interface is considered in terms of oxygen chemisorption, resulting in the formation of singly ionised molecular and atomic species, and oxygen incorporation into the zirconia lattice. The reactivity at the O2/Pt interface is considered in terms of oxygen incorporation into PtO2, which forms a thin layer covering the Pt. The derived reactivity models are used for quantitative assessment of CPD changes in terms of work function changes of yttria-stabilised zirconia (YSZ) during oxidation and reduction.