Multisegment PtRu nanorods: Electrocatalysts with adjustable bimetallic pair sites

Abstract

Multisegment PtRu nanorods (Pt-Ru, Pt-Ru-Pt, Pt-Ru-Pt-Ru, Pt-Ru-Pt-Ru-Pt, Pt-Ru-Pt-Ru-Pt-Ru) with customizable lengths of the individual metals are obtained by the sequential electrodeposition of the metals into the pores of anodic aluminum oxide (AAO) membranes. Field-emission scanning electron microscopy (FESEM) shows that the nanorods are about 200 nm in diameter and 1.2 μm long, with 900 nm of total platinum-segment length. The alternating platinum and ruthenium segments can be easily differentiated using FESEM. X-ray diffractometry reveals that the platinum and ruthenium in the bimetallic nanorods are polycrystalline with face-centered cubic and hexagonal close-packed crystal lattice structures, respectively. The presence of Pt0, PtII, PtIV, Ru0, and RuVI on the surface of the bimetallic nanorods is demonstrated via X-ray photo-electron spectroscopy. The nanorods are catalytically active in the room-temperature electro-oxidation of methanol. The relative rates of reaction, recorded using chronoamperometry, show a linear relationship between the long-time (near-steady-state) current density and the number of Pt-Ru interfaces. The use of segmented nanorods with a controlled number of Pt-Ru interfaces removes many of the ambiguities in the interpretation of experimental data from conventional alloy catalysts and has provided a direct demonstration of the role of pair sites in bifunctional catalysis. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.