Electro-oxidn. of platinum film electrode deposited on yttria-stabilized zirconia (YSZ) is examd. in situ using potential programmed voltammetry at 450 DegC in oxygen contg. atm. Under prolonged anodic oxidn. different sorts of oxidized species are formed which are consumed subsequently during a linear cathodic potential scan resulting in three distinct redn. peaks, one of them being fairly reversible while the two others strongly irreversible. Higher oxidn. potential and longer time of polarization favor the irreversible processes. The coexistence of three electrochem. processes is explained with the extension of the triple phase boundary. The rapid first process is identified as formation of PtOx at the electrode/metal interface, the second process - a much slower, parallel one - is related to the phenomenon of oxygen backspillover at the metal/gas interface, and the slowest third process - consecutive to the first one - is attributed to growth of the PtOx layer at the electrode/metal interface toward the bulk of the metal by analogy to electro-oxidn. of platinum in aq. liq. electrochem. [on SciFinder (R)]