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Probing Molecular-Scale Catalytic Interactions between Oxygen and Cobalt Phthalocyanine Using Tip-Enhanced Raman Spectroscopy
journal contribution
posted on 2018-04-23, 00:00 authored by Duc Nguyen, Gyeongwon Kang, Naihao Chiang, Xu Chen, Tamar Seideman, Mark C. Hersam, George C. Schatz, Richard P. Van DuyneUltrahigh vacuum tip-enhanced Raman
spectroscopy (UHV-TERS) is
used to investigate adsorption of molecular oxygen (O2)
on cobalt(II) phthalocyanine (CoPc) supported on Ag(111) single crystal
surfaces, which is the initial step for the oxygen reduction reaction
(ORR) using metal Pc catalysts. Two adsorption configurations are
primarily observed, assigned as O2/CoPc/Ag(111) and O/CoPc/Ag(111)
based on scanning tunneling microscopy (STM) imaging, TERS, isotopologue
substitution, and density functional theory (DFT) calculations. Distinct
vibrational features are observed for different adsorption configurations
such as the 18O–18O stretching frequency
at 1151 cm–1 for O2/CoPc/Ag(111), and
Co–16O and Co–18O vibrational
frequencies at 661 and 623 cm–1, respectively, for
O/CoPc/Ag(111). DFT calculations show vibrational mode coupling of
O–O and Co–O vibrations to the Pc ring, resulting in
different symmetries of oxygen-related normal modes. This study establishes
UHV-TERS as a chemically sensitive tool for probing catalytic systems
at the molecular scale.