Structure of Dealloyed PtCu3 Thin Films and Catalytic Activity for Oxygen Reduction

The detailed structure and composition (surface and bulk) as well as catalytic activity for oxygen reduction of electrochemically dealloyed PtCu3 thin films have been investigated. Synchrotron-based anomalous X-ray diffraction (AXRD) reveals that a Pt enriched surface region (similar to 1.0 nm thick) and a Cu depleted interior (atomic ratio different from that of PtCu3) are formed in the dealloyed film, and we directly observe a compressive lattice strain in the Pt surface region. The dealloyed PtCu3 thin films show a similar to 2.4 fold increase in the specific oxygen reduction activity over pure Pt thin films as measured by a rotating disk electrode (RDE). Our results show that the enhanced catalytic activity of the dealloyed Pt-Cu film is primarily due to the compressive strain in the surface layer (ligand effect is very weak). We compare our results on thin films to related results on nanoparticles. These studies provide a better understanding of the structure - composition and structure - activity relationships in Pt-skeleton structures prepared by dealloying base-metal-rich alloys.