Probing Molecular-Scale Catalytic Interactions between Oxygen and Cobalt Phthalocyanine Using Tip-Enhanced Raman...

Area of Science:

• Surface Science
• Catalysis
• Spectroscopy

Background:

• The oxygen reduction reaction (ORR) is crucial for energy conversion technologies.
• Metal phthalocyanines (MPcs) are promising catalysts for ORR, but their reaction mechanisms require detailed molecular-level understanding.
• Investigating the initial adsorption steps of oxygen on MPc surfaces is essential for catalyst design.

Purpose of the Study:

• To investigate the adsorption of molecular oxygen (O2) on cobalt(II) phthalocyanine (CoPc) supported on Ag(111) using UHV-TERS.
• To identify and characterize different oxygen adsorption configurations at the molecular scale.
• To establish UHV-TERS as a sensitive tool for probing catalytic systems.

Main Methods:

• Ultrahigh vacuum tip-enhanced Raman spectroscopy (UHV-TERS) for in-situ vibrational analysis.
• Scanning tunneling microscopy (STM) for imaging adsorption structures.
• Isotopologue substitution and density functional theory (DFT) calculations for vibrational mode assignment and analysis.

Main Results:

• Two primary adsorption configurations, O2/CoPc/Ag(111) and O/CoPc/Ag(111), were identified.
• Distinct vibrational frequencies were observed for O2 (1151 cm-1 for 18O-18O stretch) and O (661 cm-1 for Co-16O, 623 cm-1 for Co-18O).
• DFT calculations revealed coupling of oxygen vibrations with the CoPc ring, influencing normal mode symmetries.

Conclusions:

• UHV-TERS successfully probes the initial stages of the ORR at the molecular level.
• The study provides detailed insights into oxygen adsorption configurations on CoPc/Ag(111).
• This work validates UHV-TERS as a powerful chemical sensing technique for catalytic surface studies.