Abstract
Thick composites composed of crystalline manganese dioxide (MnO <sub>2</sub> ) and multiwall carbon nanotubes (MWCNTs) were successfully codeposited onto a graphite substrate from an Mn(AcO) <sub>2</sub> · 4H <sub>2</sub> O + MWCNTs solution. The rate/nucleation mechanism of MnO <sub>2</sub> deposition was significantly influenced by the introduction of MWCNTs in the plating baths. The specific capacitance of thick MnO <sub>2</sub> -MWCNT composites, measured from cyclic voltammetry (CV) or chronopotentiometry (CP) in a potential window of 1.0 V, is monotonously decreased from ca. 160 to 80 F/g with increasing the oxide loading from 1.5 to 4.5 mg/cm <sub>2</sub> . The lower specific capacitance of thick MnO <sub>2</sub> and MnO <sub>2</sub> -MWCNTs deposits is reasonably attributed to the relatively poorer utilization of electroactive species as well as the compact structure in comparison with a thin Mn oxide deposit (<1 μm). The capacitive performance of these thick MnO <sub>2</sub> deposits in 0.1 M Na <sub>2</sub> SO <sub>4</sub> is significantly improved by the application of electrochemical activation and the introduction of MWCNTs, revealing the promising improvement in the capacity of electrodes. © 2004 The Electrochemical Society. All rights reserved.