Role of Cerium Oxide in the Enhancement of Activity for the Oxygen Reduction Reaction at Pt–CeO_<i>x</i>Nanocomposite Electrocatalyst - An in Situ Electrochemical X-ray Absorption Fine Structure Study

Abstract

In situ electrochemical X-ray absorption fine structure (XAFS) measurements were performed at the Pt L3 and Ce L3 edges of the Pt–CeOx/C catalyst, which was prepared by a combined process of precipitation and coimpregnation methods, as well as at the Pt L3 edge of the conventional Pt/C catalyst in oxygen-saturated H2SO4 solution to clarify the role of CeOx in the reduction of the overpotential for the oxygen reduction reaction (ORR) at the Pt–CeOx nanocomposite compared with the conventional Pt/C catalyst. XAFS measurements clearly show that the enhancement of ORR activity is attributed to the inhibition of Pt oxide formation by the CeOx layer, of which Ce3+ was oxidized to Ce4+ instead of Pt at the Pt oxide formation potential.