Structural characterizations of PtRu nanoparticles by galvanostatic pulse electrodeposition

Abstract

We demonstrate that the compositions and structures of PtRu nanoparticles can be altered via adjusting plating variables during galvanostatic pulse electrodeposition. During current-on time (Ton), both Pt and Ru are deposited according to their respective diffusion-limiting current. However, during current-off time (Toff), due to difference in the redox potentials, a displacement reaction is occurring that leads to the reduction of Pt ions from the electrolyte while the Ru atoms in the PtRu nanoparticles experience oxidation reaction and corrosive dissolution simultaneously. Therefore, the duty cycle, defined as Ton/(Ton + Toff), serves as an indicator for the severity of displacement reaction that affects the PtRu makeup. Inductively-coupled mass spectrometry determines the composition as Pt83Ru17, Pt64Ru36, and Pt53Ru47 for duty cycles of 0.077, 0.111, and 0.333, respectively. Images from transmission electron microscope exhibit nanoparticles in sizes of 4-11 nm. Analysis from extended X-ray absorption fine structure (EXAFS) suggests that Pt atoms tend to segregate outward and reside at the alloy's surface upon the displacement reaction. Composition profiles from line scans of energy dispersive X-ray spectroscopy are consistent with atomic structure revealed by EXAFS. (C) 2013 Elsevier B.V. All rights reserved.