We studied oxygen reduction reaction (ORR) activities for outermost surfaces of 0.3 nm thick Co deposited on Pt(111) (Co0.3 nm/Pt(111)) bimetallic systems fabricated using molecular beam epitaxy at various Co deposition temperatures. Results show that Co0.3 nm/Pt(111) fabricated at temperatures lower than 393 K displays extra low-energy electron diffraction (LEED) spots outside the integer ones, indicating incoherent epitaxial growth of Co. A new IR band that is attributed to linearly bonded carbon monoxide (CO) on the Pt site influenced by neighboring Co atoms emerges at 2052 cm-1 for 333 K fabricated Co0.3 nm/Pt(111), in addition to the CO-Pt and CO-Co bands. With increasing fabrication temperature, the new band shifts to higher frequencies and reaches 2082 cm-1 for 773 K fabricated Co0.3 nm/Pt(111), which has a diffuse (1× 1) LEED pattern. We evaluated the dependence of the deposition temperature on the lattice parameters of the Co0.3 nm/Pt(111) and ascribed the band at 2082 cm-1 to adsorbed CO on a Pt-enriched topmost surface having 6-fold symmetry. Although the incoherent epitaxial Co layer was unstable in 0.1 M HClO4 aqueous solution, the Pt-enriched topmost surface is rather stable and the ORR activity is 10 times higher than that for clean Pt(111). The activities for Pt0.3 nm,0.6 nm/Co0.3 nm/Pt(111) artificial sandwich (superlattice) surfaces were also evaluated. The obtained results indicate that the Co atoms located at the second atomic layer strongly modify the electrocatalysis of the topmost surface.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films