PAMAM-stabilized Pt–Ru nanoparticles for methanol electro-oxidation

This work utilizes poly(amidoamine) dendrimers (PAMAM) as a protective ligand in solution to produce carbon-supported, Pt–Ru bimetallic nanoparticles for use as methanol electro-oxidation catalysts. UV–vis spectra show that after initial Pt2+ complexation with PAMAM G4OH dendrimer in water, appropriate adjustment of solution pH permits subsequent Ru3+ complexation without displacing Pt2+, demonstrating the formation of an aqueous, bimetallic solution complex. Catalysts (nominally 20 wt% metals, confirmed by AA spectroscopy) are produced by impregnating high surface area carbon black with G4OH–(Pt2+)x(Ru3+)y complex solution, drying, and activation in H2 gas at elevated temperature. XPS results show that activation in H2 at 400 °C removes virtually all of the PAMAM and reduces all of the Pt and most of the Ru to zero valence. TEM and XRD results show that the use of G4OH in the recipe is crucial for controlling metal particle size, and that the particles are crystalline with lattice parameters indicative of bimetallic Pt–Ru alloys. XRD data also suggest that G4OH promotes greater Pt–Ru alloying when Pt:Ru = 1:1. Catalytic activity for methanol oxidation increases with Ru content and is greatest for the catalyst with 1:1 Pt:Ru ratio. Per unit mass of Pt, the methanol oxidation activity of 20 wt% G4OH–PtRu/C catalyst is about 60% greater than that of E-Tek's commercially available 20 wt% PtRu catalyst.