Abstract
• SFG spectra of adsorbed CO on Pt(111) showed on-top peak in HClO 4 and NaOH solutions. • The on-top SFG peak totally disappeared in pre-peak region in NaOH solution. • The on-top SFG peak totally disappeared in the main peak region in HClO 4 solution. • Adsorbed CO was oxidized by reacting with OH − in solution via Eley-Rideal mechanism. • SFG inactive adsorbed CO was oxidized in the main peak region in NaOH solution. In situ broad band sum frequency generation (SFG) spectroscopy was applied to clarify the oxidation mechanism of adsorbed CO on Pt(1 1 1) electrode in alkaline solution in comparison with that in acidic solution. A single SFG peak due to CO adsorbed on-top site of Pt(1 1 1) was observed in the region of 1950 – 2150 cm −1 . While oxidation of adsorbed CO proceeded in a nucleation-growth mode via Langmuir–Hinshelwood (L-H) mechanism by reacting with adsorbed OH in the main peak region in 0.1 M HClO 4 solution, adsorbed CO was oxidized in a random oxidation model via Eley-Rideal (E-R) mechanism by reacting with OH − in the solution in the pre-peak region in 0.1 M NaOH solution. The main anodic peak was still observed even after the SFG peak due to on-top CO was totally disappeared by anodic oxidation in the pre-peak region, showing there existed SFG inactive adsorbed CO, although its structure was not clear.
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