Enhanced electrocatalytic oxidation of formic acid by platinum deposition on ruthenium nanoparticle surfaces

PtRu alloy nanoparticles were prepared by the spontaneous adsorption of Pt(acac)(2) on the surface of freshly prepared octanethiolate-protected ruthenium (RuSC8) nanoparticles. UV-vis spectroscopic measurements suggested that the adsorption was facilitated by the strong affinity of the platinum metal center to the ruthenium surface. Scanning tunneling spectroscopic studies showed that the resulting PtRu nanoparticles exhibited enhanced conductance as compared to the original ruthenium nanoparticles, where the adsorbed Pt centers might serve as the effective sites for electron-tunneling across the tip/particle/substrate junction. The nanoparticles were then loaded onto a glassy carbon (GC) electrode and their catalytic activities in the electro-oxidation of formic acid were examined and compared. Remarkably, despite the presence of an organic protecting monolayer on the particle surface, apparent electrocatalytic activity was observed. Voltammetric measurements suggested that a Pt skin layer was formed on the Ru nanoparticle surface, most likely as a result of electro-reduction of the adsorbed Pt(acac)(2). On the basis of the onset potential and current density in the electro-oxidation of HCOOH, the resulting PtRu nanoparticles displayed much higher electrocatalytic activity than the Ru counterparts and commercial PtRu nanoparticle catalysts from BASF. It was also found that the electrocatalytic activity of the PtRu nanoparticles was comparable to that of FePt alloy nanoparticles and PtRu bulk electrocatalysts, despite a minimal loading of Pt in the catalysts. Consistent responses were observed in electrochemical impedance spectroscopic measurements, where the charge-transfer resistance on PtRu/GC was found to be at least an order of magnitude smaller than that on Ru/GC and commercial PtRu catalysts. These measurements suggest that the PtRu thin-layer nanoparticles might be used as a promising candidate for the electrocatalytic oxidation of formic acid. (C) 2009 Elsevier B.V. All rights reserved.