The Pt/yttria-stabilized cubic zirconia (YSZ) interface exposed to a reactive gas was characterised by solid electrolyte potentiometry and cyclic voltammetry. The catalytic reactions included total combustion of C3H8 and C3H6 to CO2 and H2O as well as NO reduction by C3H6 in the presence of O-2 under oxygen-rich and stoichiometric conditions. The solid electrolyte potentiometry as a function of the temperature in C3Hx/O-2 (with x = 6 or 8) reflected the catalytic properties of Pt for C3Hx oxidation. In C3H6/NO/O-2, the reduction of NO was evidenced below 300 degreesC. The cyclic voltammetry evidenced the formation of an oxygen chemisorbed layer on the Pt surface under anodic potential. Propane had no effect on this chemisorbed layer, whereas propene weakened significantly the strength of this Pt-O bond. Addition of NO to C3H6/O-2 led to the disappearing of this chemisorbed layer. The use of solid electrolyte potentiometry in conjunction with cyclic voltammetry allowed us to determine the surface oxidation state of Pt during the catalytic reactions. (C) 2003 Elsevier B.V. All rights reserved.