Surface Structures and Electrochemical Stabilities for Pt/Pd(111) Model Electrocatalysts

摘要

We investigated surface structures and electrochemical stabilities for Pt/Pd(111) bimetallic surfaces fabricated using molecular beam epitaxy. The Pt/Pd(111) surfaces were prepared by depositing four monolayer (ML)-thick Pt onto Pd(111) at substrate temperatures of 300°C. The oxygen reduction reaction (ORR) activity of the pristine 4ML-Pt/Pd(111) surface was ca. 4.5 times higher than that of clean Pt(111). Electrochemical stabilities were evaluated by applying square-wave potential cycles (PCs) between 0.6 and x V (x = 0.8, 0.85, 0.9 and 1.0; xV-PCs) in O_2-saturated 0.1 M HClO_4 at 80°C. Although the 0.9V- and 1.0V-PCs cause ORR deactivation, the pristine ORR activities remained nearly unchanged by the 0.8V- and 0.85V-PCs even after 5000 PCs. The results suggest that the electrochemical structural stability of Pt/Pd core-shell type catalysts depends on the cell voltages used under the practical operating conditions of polymer electrolyte fuel cells.