Electrochemical Scanning Tunneling Microscopic Observation of the Preoxidation Process of CO on Pt(111) Electrode Surface

Presented are sequential images of CO on Pt(111), observed with electrochemical scanning tunneling microscopy, during its electrochemical preoxidation process. In the course of the well-known phase transition from the (2 × 2)-3CO-α structure to the (√19 × √19)R23.4°-13CO structure, various structures were observed: (2 × 2)-3CO-β (Chem. Comm. 2006, 2191−2193), (1 × 1)-CO, and (√13 × √13)R46.1°-9CO. Based on an analysis of the populations of the structures averaged over imaging time and imaged location at the preoxidation potential range (0−0.25 V vs Ag/AgCl), the structures of CO domains changed sequentially in the order of (2 × 2)-3CO-α, (2 × 2)-3CO-β, (1 × 1)-CO, (√13 × √13)R46.1°-9CO, and (√19 × √19)R23.4°-13CO as the potential shifted from 0 to 0.25 V. Such a sequential structural change demonstrates that the structures of (2 × 2)-3CO-β, (1 × 1)-CO, and (√13 × √13)R46.1°-9CO are transient ones during the preoxidation of CO on Pt(111). Discussed are the transient structures in terms of various aspects, such as the absence of CO in solution and the origin of compressed structures.