The electrochemical response of manganese hydroxide± oxide ®lms in slightly alkaline solutions. II. Voltammetric and ellipsometric studies

M. HERNANDEZ UBEDA; H. HERRERA; H. T. MISHIMA; B. A. LÓPEZ DE MISHIMA; H. M. VILLULLAS; M. LÓPEZ TEIJELO

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1998 vol. 44 p. 513 - 519

0013-4686

The potentiodynamic behaviour of colloidal manganese hydroxide±oxide ®lms obtained by chemical precipitation on a conducting substrate in alkaline solutions is described. The voltammetric response of cycled electrodes 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 reportedfor manganese and iridium oxides obtained by cycling the base metal. The optical response of cycled hydrous manganese oxide ®lms is studied by in-situ ellipsometry. Data can be explained using an anisotropic single layer model. The optical anisotropy is related to the morphology of the hydrous oxide layer. The electroreduction process produces a decrease of the refractive indices and a pronounced diminution of the extinction coe?cients yielding apractically transparent film.