Synergistic Effects of Fe2O3 Nanotube/Polyaniline Composites for an Electrochemical Supercapacitor with Enhanced Capacitance

Abstract

alpha-Fe2O3, which is an attractive material for supercapacitor electrodes, has been studied to address the issue of low capacitance through structural development and complexation to maximize the use of surface pseudocapacitance. In this study, the limited performance of alpha-Fe2O3 was greatly improved by optimizing the nanotube structure of alpha-Fe2O3 and its combination with polyaniline (PANI). alpha-Fe2O3 nanotubes (alpha-NT) were fabricated in a form in which the thickness and inner diameter of the tube were controlled by Fe(CO)(5) vapor deposition using anodized aluminum oxide as a template. PANI was combined with the prepared alpha-NT in two forms: PANI@alpha-NT-a enclosed inside and outside with PANI and PANI@alpha-NT-b containing PANI only on the inside. In contrast to alpha-NT, which showed a very low specific capacitance, these two composites showed significantly improved capacitances of 185 Fg(-1) for PANI@alpha-NT-a and 62 Fg(-1) for PANI@alpha-NT-b. In the electrochemical impedance spectroscopy analysis, it was observed that the resistance of charge transfer was minimized in PANI@alpha-NT-a, and the pseudocapacitance on the entire surface of the alpha-Fe2O3 nanotubes was utilized with high efficiency through binding and conductivity improvements by PANI. PANI@alpha-NT-a exhibited a capacitance retention of 36% even when the current density was increased 10-fold, and showed excellent stability of 90.1% over 3000 charge-discharge cycles. This approach of incorporating conducting polymers through well-controlled nanostructures suggests a solution to overcome the limitations of alpha-Fe2O3 electrode materials and improve performance.