Detection of Superoxide Anion Oxygen Reduction Reaction Intermediate on Pt(111) by Infrared Reflection Absorption Spectroscopy in Neutral pH Conditions

In this work, in situ external infrared reflection absorption spectroscopy (IRRAS) is successfully employed for the detection of intermediate species in the oxygen reduction reaction (ORR) mechanism on a flat and well-defined Pt surface. Superoxide anion species (O2-) are detected on the Pt(111) surface in an O2-saturated solution with a NaF/HClO4 mixture with pH 5.5 by the observation of a O-O vibration band at ca. 1080 cm-1. The observation of O2- without the use of any other additional method of signal enhancement is possible because in these experimental conditions O2- is the main ORR-generated intermediate and its reactivity is limited in this pH. This leads to the accumulation of O2- near the Pt surface, facilitating its identification.