New experimental evidence on the formation of platinum superactive sites in an electrochemical environment

V DÍAZ; S REAL; E TÉLIZ; CF ZINOLA; ME MARTINS*

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY

ELSEVIER

Año: 2008

0360-3199

Abstract New electrochemical results are found after the application of a constant cathodic polarization to the platinum/aqueous acid solution interface within the hydrogen evolution region. Voltammograms reveal highly stable anodic peaks emerging in the double-layer region assigned to the so-called “superactive” states. The severe cathodization produces the disruption of the platinum/aqueous solution interface leading to an open outer layer composed of metallic species highly coordinated to the solvent. These active sites are related with electrocatalytic features since the onset potential for water discharge is diminished. Voltammetry and modulated voltammetry explain the fact that platinum species highly coordinated to the solvent can be more oxidized since the reduction potential shifts toward more negative values. The alkalinization of the interface and the formation of new surface oxides in a different potential range are proposed. The latter produces electrocatalytic effects on methanol electrooxidation. Keywords: platinum; superactive state; triangularly modulated triangular potential sweep voltammetry; electrochemical impedance; XPS.