2 H MAS NMR and SPECS Studies of γ ­ MnO2 Reduction in Zinc Alkaline Primary Batteries

Abstract

magic-angle spinning (MAS) NMR spectroscopy was used, in conjunction with step potential electrochemical spectroscopy (SPES), to investigate the reduction and H-insertion mechanisms of in primary zinc alkaline batteries. Three electrolytic manganese dioxides (EMDs) were discharged in a deuterated alkaline electrolyte: a commercial EMD, and two synthetic EMDs, one prepared in a static electrolyte, and the other in a deuterated static electrolyte. Five distinct discharge processes were observed in the SPES plots, which were assigned to reduction of near defects (1.45 V), reduction of ramsdellite and pyrolusite domains (1.1-1.3 V), formation of (1.05 V), and reduction of Mn(III) to Mn(II) (0.95 V). The signal intensities increase up to ca. 50% of discharge and then decrease on further discharge due to the growth of non-proton-containing oxides, such as and The MAS NMR spectra of the 1.4 V discharged products of all samples were dominated by an isotropic resonance at around 300 ppm, which is assigned to deuteron environments near defects (e.g., Mn-vacancy sites). The results were compared to those for three model compounds with different levels of De Wolff disorder, 0.61, 0.99. © 2004 The Electrochemical Society. All rights reserved.