Long-range structural effects in the anomalous voltammetry on ultra-high vacuum prepared Pt (111)

Abstract

The cyclic voltammetry of Pt (111) in three different structural states (well-ordered, restructured by electrochemical redox cycling, and restructured by Ar +-sputtering) was studied in aqueous acidic and basic electrolytes using a UHV-electrochemical transfer system. The well-ordered surface gave distinctive voltammograms with anomalous features identical to those first reported by Clavilier using flame-an-nealed (111) surfaces transferred through the air while hot. Electrochemical cycling above the sharp oxidation peak removed the anomalous features and introduced randomly spaced monatomic steps to the surface, as shown by low energy electron diffraction (LEED). Ar +-sputtered surfaces, with a similar randomly stepped structure, yielded on the first cycle the same voltammetry as the redox-cycled surfaces, demonstrating clearly that the loss of the anomalous features upon cycling is due to a disruption of the long-range (> 5 atomic spacings) order of the surface, rather than to a simple irreversible oxidation of adventitious impurities. Cycling in basic electrolytes produced voltammetric and structural changes similar to those seen in acid. Possible origins of the anomalous features are discussed in the light of the collected electrochemical and surface science data. The extreme sensitivity of these systems to disruption of long-range surface order is ascribed to the ability of hydrogen-bonded aqueous networks to transmit structural phase information over greater-than-molecular distances.