Electrochemical impedance spectroscopy has been used to characterize various electrode constructions employing electrolytic manganese dioxide (EMD), the active material used in alkaline manganese dioxide cathodes. The electrodes varied in their access to electrons necessary for reduction. The results suggest that establishing an effective three-phase boundary between EMD, graphite, and the alkaline electrolyte is essential for low impedance behavior. Furthermore, the processes of proton and electron insertion into the structure to cause reduction must occur in close proximity to one another, implying a commercial cathode performance dependence on factors such as mixing, packing, and EMD and graphite particle size. Evidence is also presented to support localization of proton-electron pairs within the structure, rather than delocalization, which is apparent in the literature, as well as the extent to which electrolyte can penetrate into the porous EMD structure. (c) 2007 The Electrochemical Society.