Morphology of Template-Grown Polyaniline Nanowires and Its Effect on the Electrochemical Capacitance of Nanowire Arrays

The morphology of polyaniline nanowires grown electrochemically in anodic aluminum oxide (AAO) templates is strongly influenced by the supporting electrolyte concentration, the potential of electropolymerization, the growth time, and the monomer concentration. Increasing the sulfuric acid concentration during growth induces a transition from solid nanowires with tubular ends to open nanowires. Current transient data for nanowire growth were interpreted quantitatively in terms of instantaneous and progressive nucleation and growth models, and this analysis was consistent with the observed concentration and potential dependence of nanowire vs nanotube growth. The electrochemical capacitance of nanowire arrays in AAO templates was shown to be related to the morphology of the nanowires. Specific capacitance values in the range of 700 F/g (measured at a charge/discharge rate of 5 A/g) were obtained for porous nanowires grown at 0.5 M aniline concentration at high overpotential in 1.5−2.0 M sulfuric acid solutions.