文摘
The dependence of adsorbate vibrational frequencies on the surface potential, (“Stark‐tuning” effect), observed in electrochemical systems is exploited for the same metal surfaces in contact with ambient‐pressure gases so to estimate values in the latter environment. Saturated CO adlayers on palladium and platinum films are examined along these lines by using surface‐enhanced Raman spectroscopy (SERS) to obtain frequencies for both the C–O () and metal–carbon stretching () vibrations in CO‐containing aqueous electrochemical and gaseous environments. The effective gas‐phase surface potentials extracted by matching the vibrational frequencies with the corresponding potential‐dependent electrochemical spectra are substantially (ca. 1–1.5 V) lower than the work functions for such interfaces under “clean” (ultrahigh vacuum) conditions. These disparities are ascribed to the occurrence of electrochemical‐like redox half‐reactions in the ambient‐pressure gas‐phase environment, leading to surface charging, and, hence, marked alterations in the surface potential as controlled by potential‐dependent redox kinetics. The possible implications of these and related findings to ambient‐pressure adsorption and catalysis are discussed.
