The adsorption of O-18(2) on porous electropromoted Pt films deposited on Y2O3-stabilized ZrO2 (YSZ) and on nanodispersed Pt catalysts deposited on YSZ powder was investigated via TPD. The TPD spectra are very similar for both systems: When O-18(2) adsorption takes place above 200 degreesC, two O adsorption states (beta(2) and beta(3) states) form, which desorb at 425 and 500 degreesC, respectively. The latter is always occupied by lattice oxygen. For O-18(2) adsorption temperatures below 100 degreesC a weakly bonded state (beta(1) state) forms in addition to the beta(2) and beta(3) states. It desorbs at 100-160 degreesC and is occupied exclusively by O-18. Both the Pt film and the nanodispersed Pt catalyst act as oxygen portholes and mediate, via O spillover and backspillover, respectively, the incorporation of gaseous O-18(2) into the YSZ lattice during adsorption as well as the desorption of lattice O-16 during TPD. The excess oxygen stored in YSZ plays a key role in interpreting the TPD spectra. The observed very strong similarity between the O-2 TPD spectra of electrochemically promoted Pt/YSZ films and nanodispersed Pt/YSZ powder catalysts corroborates the mechanistic equivalence of electrochemical promotion and metal-support interactions (MSI) with O2--conducting supports. (C) 2003 Elsevier Inc. All rights reserved.