Kinetic characterization of PtRu fuel cell anode catalysts made by spontaneous Pt deposition on Ru nanoparticles

Hydrogen oxidation kinetics without and with trace amounts of CO in H-2 were investigated for carbon-supported catalysts consisting of Pt submonolayers on Ru nanoparticles prepared by spontaneous deposition and commercial Pt, Ru, and PtRu alloy catalysts. Thin catalyst layers were deposited onto a glassy carbon rotating disk electrode without using Nafion film to stabilize them. Nonlinear fittings of the entire polarization curves at several rotation rates were used to determine the exchange current, the Tafel slope, and the Levich slope. To ensure full utilization of the catalyst, the mass-specific activity was determined by finding the minimum Pt loading needed to have all three kinetic parameters close to those found for a polycrystalline Pt electrode. For the PtRu20, PtRu10, and PtRu5 samples prepared by spontaneous deposition of 1/9 to 4/9 monolayer Pt on Ru, the minimum loading is 5 nmol/cm(2) (1 mug(Pt)/cm(2)). This is only one-third of that for Pt or PtRu (E-TEK) catalysts and only double the atomic density of a Pt(111) surface, indicating that the high activity of Pt metal for hydrogen oxidation is retained when the atomic assemblies are reduced to submonolayer level on Ru. The enhanced CO tolerance was studied at low potentials by correlating the loss of the activity in 0.1% CO/H-2 with the CO coverage on Pt and Ru sites. (C) 2003 The Electrochemical Society.