Manganese dioxides surface properties studied by XPS and gas adsorption

Structurally well defined gamma-MnO2 in terms of Pr and Tw were studied using X-ray photoelectron spectroscopy (XPS) to complete surface investigations performed by high-resolution gas adsorption, water adsorption, and acid-base surface titration. The O 1s and Mn 2p spectra were deconvoluted into three components Mn-OH2+, Mn-OH, and Mn-O-. Analysis of the O 1s spectra in energy shift and relative intensity shows that 70 to 80% of the surface groups stay as neutral OH, 5% as Mn-OH2 and 20 to 30% as Mn-OH: their relative amount varies with Pr as well as PZC, water cross-sectional area and energetic constant C. Mn 2p spectra are far less sensitive than O 1s to the charge variation. Nevertheless a correlation is shown between the relative amount of surface species, the binding energy of Mn = O and O = Mn species and Tw. (C) 2004 The Electrochemical Society.