Template preparation of multisegment PtNi nanorods as methanol electro-oxidation catalysts with adjustable bimetallic pair sites

Multisegment PtNi nanorods (Ni-Pt, Ni-Pt-Ni, Ni-Pt-Ni-Pt, and Ni-Pt-Ni-Pt-Ni) with controllable lengths of the individual metals were obtained by sequential electrodeposition of the metals into the pores of anodic aluminum oxide (AAO) membranes. Field emission scanning electron microscopy (FESEM) showed that the nanorods are about 170 nm in diameter and 1.6 mum in length, with 530 nm of total Pt segment lengths. The alternating Pt and Ni segments could be easily differentiated by FESEM. XRD characterization of the PtNi nanorods indicated that both Pt and Ni are polycrystals with a face-centered cubic structure. The presence of Pt(0), Pt(II), Pt(IV), Ni(0), and Ni(II) on the surface of the PtNi nanorods was deduced from XPS measurements. The nanorods are catalytically active in the room temperature electro-oxidation of methanol. The relative rates of reaction as recorded by cyclic voltammetry showed a linear relationship between the peak current densities and the number of Pt-Ni interfaces. The use of segmented nanorods with identifiable Pt-Ni 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 the bifunctional mechanism.