THE ELECTROCHEMICAL RESPONSE OF MANGANESE HYDROXIDE OXIDE-FILMS IN SLIGHTLY ALKALINE-SOLUTIONS - II - VOLTAMMETRIC AND ELLIPSOMETRIC STUDIES

The potentiodynamic behaviour of colloidal manganese hydroxide-oxide f ilms obtained by chemical precipitation on a conducting substrate in a lkaline solutions is described. The voltammetric response of cycled el ectrodes shows a main redox couple which is associated with the Mn(III )/Mn(IV) reaction occurring in solid state. The observed dependence of peak currents and peak potentials on sweep rate, charge and solution pH is similar to that reported for manganese and iridium oxides obtain ed by cycling the base metal. The optical response of cycled hydrous m anganese oxide films is studied by in-situ ellipsometry. Data car, be explained using an anisotropic single layer model. The optical anisotr opy is related to the morphology of the hydrous oxide layer. The elect roreduction process produces a decrease of the refractive indices and a pronounced diminution of the extinction coefficients yielding a prac tically transparent film. (C) 1998 Elsevier Science Ltd. All rights re served.