Abstract
α-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 α-Fe2O3 was greatly improved by optimizing the nanotube structure of α-Fe2O3 and its combination with polyaniline (PANI). α-Fe2O3 nanotubes (α-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 α-NT in two forms: PANI@α-NT-a enclosed inside and outside with PANI and PANI@α-NT-b containing PANI only on the inside. In contrast to α-NT, which showed a very low specific capacitance, these two composites showed significantly improved capacitances of 185 Fg−1 for PANI@α-NT-a and 62 Fg−1 for PANI@α-NT-b. In the electrochemical impedance spectroscopy analysis, it was observed that the resistance of charge transfer was minimized in PANI@α-NT-a, and the pseudocapacitance on the entire surface of the α-Fe2O3 nanotubes was utilized with high efficiency through binding and conductivity improvements by PANI. PANI@α-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 α-Fe2O3 electrode materials and improve performance.
Highlights
As electrical energy storage devices, electrochemical supercapacitors have the characteristics of high power, fast charge–discharge, high cycle efficiency, and stability
It was found that Fe(CO)5 selectively decomposed on the alumina surface to form metallic iron, and this enabled the fabrication of α-Fe2 O3 nanotubes with a precisely controlled tube thickness and diameter
The very low capacitance of α-Fe2O3 nanotubes (α-NT) was dramatically increased by the formation of combined structures with PANI
Summary
As electrical energy storage devices, electrochemical supercapacitors have the characteristics of high power, fast charge–discharge, high cycle efficiency, and stability. These characteristics cannot be fully realized in current lithium-ion battery technology; the importance of the energy storage role of the supercapacitor in various mobile devices is increasing. The limit of the energy storage density is always an obstacle to allow the supercapacitor to be the main storage device This is due to the basic principle that supercapacitors directly store electric charge on the electrode surface. This principle results in high power, and causes low energy storage density [1,2]. MnO2 [3,4,5,6], NiO [7,8], and RuO2 [9,10]-based materials have been developed to exhibit pseudocapacitance with high charge storage capacity; beginning to overcome the limitations of low-capacity
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