Abstract
Highly ordered titania nanotubes (TNTs) were synthesised by an electrochemical anodization method for supercapacitor applications. However, the capacitive performance of the TNTs was relatively low and comparable to the conventional capacitor. Therefore, in order to improve the capacitive performance of the TNTs, a fast and facile electrochemical reduction method was applied to modify the TNTs (R-TNTs) by introducing oxygen vacancies into the lattice. X-ray photoelectron spectroscopy (XPS) data confirmed the presence of oxygen vacancies in the R-TNTs lattice upon the reduction of Ti4+ to Ti3+. Electrochemical reduction parameters such as applied voltage and reduction time were varied to optimize the best conditions for the modification process. The electrochemical performance of the samples was analyzed in a three-electrode configuration cell. The cyclic voltammogram recorded at 200 mV s−1 showed a perfect square-shaped voltammogram indicating the excellent electrochemical performance of R-TNTs prepared at 5 V for 30 s. The total area of the R-TNTs voltammogram was 3 times larger than the unmodified TNTs. A specific capacitance of 11.12 mF cm−2 at a current density of 20 μA cm−2 was obtained from constant current charge-discharge measurements, which was approximately 57 times higher than that of unmodified TNTs. R-TNTs also displayed outstanding cycle stability with 99% capacity retention after 1000 cycles.
Highlights
Global energy crisis, the depletion of fossil fuels, and the ever increasing environmental pollution have all led to an urgent search of efficient, clean, and sustainable alternative energy supply and storage
The geometrical size of the nanotubes tended to reduce after electrochemical reduction, but the structure of the nanotubes was still intact
A fast and simple electrochemical reduction method in an aqueous electrolyte has been presented in this work in order to enhance the capacitive performance of TNTs as a supercapacitor
Summary
The depletion of fossil fuels, and the ever increasing environmental pollution have all led to an urgent search of efficient, clean, and sustainable alternative energy supply and storage. Due to the increased power demand worldwide, there has been a need to develop high power and high energy devices that are robust and are able to withstand hundreds and thousands of charging/discharging cycles without being degraded. Electrochemical capacitors, known as ultracapacitors and supercapacitors, have attracted significant attention, mainly due to their promising properties: higher power density than batteries, higher energy density than conventional capacitors, fast charging-discharging rates, and prolonged cycle life [1]. Supercapacitors are characterized as electric double-layer capacitors (EDLC) and pseudocapacitors. Electrical energy storage in EDLC occurs at the phase boundary between the electrode (active material) and the electrolyte solution (liquid ionic conductor) [2] with no charge-transfer involvement. As for pseudocapacitors, charge storage is caused by the fast faradaic redox reaction due to Journal of Nanomaterials
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