Crystallized manganese dioxide powders (cryptomelane type alpha-MnO2 and birnessite type delta-MnO2) were electrochemically investigated in mild aqueous electrolytes with the cavity microelectrode (CME) technique. Cyclic voltammetry was performed with isolated MnO2 powder and mixed acetylene black/MnO2 powder. High electrochemical performance is achieved showing the pseudocapacitive behavior of cryptomelane and the birnessite signature, which is exhibited by large, intense and more defined peaks, than for a composite electrode. The microcavity electrode (about 10(-3) mm(3)) allows studies with only a few micrograms of MnO2 powder in order to display its intrinsic electrochemical behavior and to improve the understanding of the role of the different components in the composite electrode performance. (C) 2012 Elsevier Ltd. All rights reserved.