H-2 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 gamma-MnO2 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 MnO2 near defects (1.45 V), reduction of ramsdellite and pyrolusite domains (1.1-1.3 V), formation of ZnMn2O4 (1.05 V), and reduction of Mn(III) to Mn(II) (0.95 V). The H-2 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 Mn2O3, Mn3O4, and ZnMn2O4. The H-2 MAS NMR spectra of the 1.4 V discharged products of all gamma-MnO2 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 gamma-MnO2 model compounds with different levels of De Wolff disorder, P-r approximate to 0.25, 0.61, 0.99. (C) 2004 The Electrochemical Society.