Spectroelectrochemical studies of birnessites

Abstract

Layered manganese dioxides, birnessites, have been studied by cyclic voltammetry and Raman spectroscopy. Electrochemical polarisations have been carried out using two types of electrode coatings; thin film and a thicker birnessite/graphite/Teflon composite. Raman spectroscopy shows heterogeneous phase transformation of hydrogen bimessite to Mn2O3 at high negative potentials. The addition of Li+ to the working solution leads to intercalation of Li+ ions and a change of electrochemical behaviour of the birnessites to reversible reduction-oxidation of MnO2. Under these conditions the Raman spectra do not show "structural collapse" to Mn2O3. Polarisation data for amine salts and for aniline are comparable for these of Li+ where intercalation has occured. Cyclic voltammetry in organic solution also demonstrates the absence of any phase transformation and points to the reversible behaviour of birnessites. A good correlation of electrochemical and spectroscopic results have been obtained.