PtRu Alloy Nanoparticles. 2. Chemical and Electrochemical Surface Characterization for Methanol Oxidation

Platinum–ruthenium (PtRu) nanoparticles (NPs) were evaporatively deposited in a 1:1 mass ratio onto carbon paper, using three different orders of deposition: Pt deposited onto Ru, Ru deposited onto Pt, and both Pt and Ru deposited simultaneously. The three samples were further annealed at 650 °C for 1.5 h. A sample of Pt NPs on carbon paper was also prepared as a reference. All the deposits and the reference (a total of seven samples) were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and electrochemical techniques, in order to investigate the relationship between their catalytic surface chemical properties and their electrocatalytic activities during the methanol oxidation reaction. The simultaneous deposition of Pt and Ru demonstrated higher electrocatalytic activity, as well as excellent chronoamperometric stability, compared to either sequential deposition. This can be attributed to the synergistic effects between Pt and Ru species at the surface. Annealing at 650 °C led to a reduction of the electrocatalytic oxidation peaks. This appears to be due to the deposition of surface hydrocarbons at high temperature, thereby blocking active catalysis sites on the NP surface, as well as to the decomposition of metal oxides, which occurs above 350 °C.