The structural and chemical heterogeneity of 2.5-nm
Pt50Ru50 electrocatalysts was studied
by transmission electron microscopy using selected area
diffraction, lattice imaging, electron-energy loss spectroscopy,
and energy-dispersive X-ray spectroscopy. The catalysts with
the highest methanol oxidation activities exhibit oxidation-induced
phase separation on the nanoscale to form Pt-rich metal embedded
in Ru-rich hydrous and anhydrous oxide. Reduction of the
oxide-on-metal samples produces a true bimetallic face-centered
cubic Pt50Ru50 alloy, with 275 times lower
oxidation activity.
