Lamellar birnessite-type MnO2 materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO2 with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO2, composed of alpha-MnO2 and gamma-MnO2, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO2 Was much higher than that of rod-like MnO2 at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO2. The initial specific capacitance of MnO2 prepared at pH 2.81 was 242.1 F g(-1) at 2 mA cm(-2) in 2 mol L-1 (NH4)(2)SO4 aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm(-2). (C) 2009 Elsevier Ltd. All rights reserved.