Multisegment PtRu nanorods: Electrocatalysts with adjustable bimetallic pair sites

Multisegment PtRu nanorods (Pt-Ru, Pt-Ru-Pt, Pt-Ru-Pt-Ru, Pt-Ru-Pt-Ru-Pt, Pt-Ru-Pt-Ru-Pt-Ru) with customixable lengths of the individual metals are obtained by the sequential electrodeposition of the metals into the pores of anodic amulinum oxide (AAO) membranes. Field-emission scanning electron microscopy (FESEM) shows that the nanorods are about 200nm in diameter and 1.2 mu m long, with 900 nm of total platinum-segment length. The alternating platinum and ruthenium segments can be easily differentiated using FESEM. X-ray diffractomy reveals that the platinum and ruthenium in the bimetallic nonorods are polycrystalline with face-centered cubic and hexagonal close-packed crystal lattice structures, respectively. The presence of Pt-0, Pt-II, Pt-IV, Ru-0, and Ru-VI on the surface of the bimetallic nanorods is demonstrated via X-ray photo-electron spectroscopy. The nanorods are catalytically active in the room-temperature electron-oxidation of methanol. The relative rates of reaction, recorded using chronoamperometry, show a linear relationship between the long-time (near-study-state) current density and the number of Pt-Ru interfaces. The use of segmented nanorods with 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.