Effects of electrochemical activation and multiwall carbon nanotubes on the capacitive characteristics of thick MnO2 deposits

Thick composites composed of crystalline manganese dioxide (MnO2) and multiwall carbon nanotubes (MWCNTs) were successfully codeposited onto a graphite substrate from an Mn(AcO)(2) .4H(2)O + MWCNTs solution. The rate/ nucleation mechanism of MnO2 deposition was significantly influenced by the introduction of MWCNTs in the plating baths. The specific capacitance of thick MnO2-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(2). The lower specific capacitance of thick MnO2 and MnO2-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 mu m). The capacitive performance of these thick MnO2 deposits in 0.1 M Na2SO4 is significantly improved by the application of electrochemical activation and the introduction of MWCNTs, revealing the promising improvement in the capacity of electrodes. (C) 2004 The Electrochemical Society.