Pt metal-CeO2 interaction: Direct observation of redox coupling between Pt/Pt2+/Pt4+ and Ce4+/Ce3+ states in Ce0.98Pt0.02O2−δ catalyst by a combined electrochemical and x-ray photoelectron spectroscopy study

Abstract

Pt ions- CeO 2 interaction in Ce 1 − x Pt x O 2 − δ ( x = 0.02 ) has been studied for the first time by electrochemical method combined with x-ray diffraction and x-ray photoelectron spectroscopy. Working electrodes made of CeO 2 and Ce 0.98 Pt 0.02 O 2 − δ mixed with 30% carbon are treated electrochemically between 0.0–1.2 V in potentiostatic (chronoamperometry) and potentiodynamic (cyclic voltametry) mode with reference to saturated calomel electrode. Reversible oxidation of Pt 0 to Pt 2 + and Pt 4 + state due to the applied positive potential is coupled to simultaneous reversible reduction of Ce 4 + to Ce 3 + state. CeO 2 reduces to CeO 2 − y ( y = 0.35 ) after applying 1.2 V, which is not reversible; Ce 0.98 Pt 0.02 O 2 − δ reaches a steady state with Pt 2 + : Pt 4 + in the ratio of 0.60:0.40 and Ce 4 + : Ce 3 + in the ratio of 0.55:0.45 giving a composition Ce 0.98 Pt 0.02 O 1.74 at 1.2 V, which is reversible. Composition of Pt ion substituted compound is reversible between Ce 0.98 Pt 0.02 O 1.95 to Ce 0.98 Pt 0.02 O 1.74 within the potential range of 0.0–1.2 V. Thus, Ce 0.98 Pt 0.02 O 2 − δ forms a stable electrode for oxidation of H 2 O to O 2 unlike CeO 2 . A linear relation between oxidation of Pt 2 + to Pt 4 + with simultaneous reduction in Ce 4 + to Ce 3 + is observed demonstrating Pt – CeO 2 metal support interaction is due to reversible Pt 0 / Pt 2 + / Pt 4 + interaction with Ce 4 + / Ce 3 + redox couple.