Effects of Electrochemical Activation and Multiwall Carbon Nanotubes on the Capacitive Characteristics of Thick MnO[sub 2] Deposits

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