Oxygen as Redox Mediator in Scanning Electrochemical Microscopy. Application to the Study of Localised Acid Attack of Marble

摘要

Oxygen from air-saturated aqueous solutions was employed as redox mediator in SECM experiments. Accurate approach curves under negative-feedback conditions were obtained using platinum and gold microelectrodes. Imaging experiments were also carried out, using a 2.5 #mu#m gold microelectrode and oxygen that acted as distance mediator. The topographic images of a glass surface and that of a marble surface prior and after localised acid attack were recorded. High concentrations of hydrogen ions were produced locally, at the microelectrode tip held 3 #mu#m above the marble surface, by applying a large enough positive potential within the oxygen evolution region. Under these conditions, the dissolution of CaCO_3 occurred. Pits were produced, and the crater volumes thus obtained were linearly dependent on the electrolysis time.