Oxygen storage in O2/Pt/YSZ cell

The phenomenon of electrochemical promotion of catalysis (EPOC) was initially characterized as fully reversible, i.e. the catalyst restores its initial activity after current interruption. However, it has been recently demonstrated that after prolonged anodic polarization an unusual promoted activity is observed for a certain time after current interruption. This phenomenon has been reported as permanent electrochemical promotion of catalysis (P-EPOC). In this work the oxygen storage reported as responsible of P-EPOC has been investigated by transient electrochemical techniques using an O2(g)Pt/YSZ cell. A model has been proposed involving place interchange of Pt and O species in Pt/YSZ system. This seems to be induced by the strong lateral interaction of Pt–O surface dipoles and by increasing electric field at the Pt/YSZ interface. Such a rearranged oxide, so-called “phase oxide” can have a lower free energy than the initial monolayer oxide. This cooperative interaction of Pt and O species can lead to further thickening of this “phase oxide” especially at high temperature and potentials (currents). Furthermore, as the charge involved in this oxide thickening shows a t1/2 dependency, the process seems to be diffusion controlled.