Synthesis of Intermetallic PtZn Nanoparticles by Reaction of Pt Nanoparticles with Zn Vapor and Their Application as Fuel Cell Catalysts

Intermetallic PtZn nanoparticles with stable and high activities toward formic acid and methanol electrooxidation were synthesized by reaction of carbon-supported Pt nanoparticles with Zn vapor at 500 degrees C for 8 h under flowing nitrogen at atmospheric pressure. The resulting well-dispersed 3-15 nm diameter PtZn nanoparticles were tetragonal phase (P4/mmm: a = 0.2842(1) nm, c = 0.3488(3) nm) and their Pt:Zn ratio was approximately 1:1. Reactions using unsupported Pt nanoparticles (< 5 nm domain size) produced aggregated masses consisting of 5-60 nm nanoparticles. The catalytic activities of supported PtZn nanoparticles toward formic acid and methanol electrooxidation were studied by differential electrochemical mass spectrometry (DEMS). The intermetallic PtZn nanoparticles exhibited higher currents For both formic acid and methanol oxidation than supported Pt nanoparticles with similar particle sizes, but the activity was not as high as that of PtPb. Finally, we established that vapor phase reactions of nano-Pt and M at temperatures sufficient to produce a vapor pressure of 1 x 10(-4) atm for M are generally successful (M: Bi, Tl, and Pb).