Abstract
Amorphous hydrous manganese oxide (a-MnO 2 ·nH 2 O) was anodically deposited onto a graphite substrate from a MnSO 4 ·5H 2 O solution with pH of 6.4. The specific capacitance of this thick a-MnO 2 ·nH 2 O deposit, measured from both cyclic voltammetry and chronopotentiometry, is about 265-320 F g -1 in a potential window of 1.0 V. The electrochemical reversibility of redox couples at/within the a-MnO 2 ·nH 2 O was significantly influenced by the pH of the test electrolytes. This amorphous hydrous oxide exhibited ideal capacitive behavior (acceptable capacity, high reversibility and high pulse charge-discharge property) between 0 and 1.0 V in 0.1 M Na 2 SO 4 indicating a promising electrode material for electrochemical supercapacitors. © 2002 Elsevier Science B.V. All rights reserved.