Hierarchical three-dimensional MnO2/carbon@TiO2 nanotube arrays for high-performance supercapacitors

Abstract

Highly ordered TiO₂ nanotube arrays (TNAs) modified by other materials with enhanced conductivity and capacitance have been considered to be promising anode materials for supercapacitors. In this work, carbon@TiO₂ nanotube arrays (CTNAs) were firstly synthesized through a calcination process under an Ar atmosphere. Then the hierarchical three-dimensional MnO₂/carbon@TiO₂ nanotube arrays (CMTNAs) were further developed via hydrothermal deposition of uniformly dispersed MnO₂ nanoparticles with the help of the in situ reduction effect of the as-obtained carbon layers. The CTNA electrode exhibited a high area capacitance of 5.58 mF cm⁻² at a scan rate of 100 mV s⁻¹, which is about 11 times higher than that of the TiO₂ nanotube arrays annealed under an air atmosphere (ATNAs). The highest gravimetric capacitance 521.4 A g⁻¹ was achieved with the CMTNAs at a current density of 2 A g⁻¹, and 88.6% of the initial capacitance could be maintained at a current density of 5 A g⁻¹ up to 2000 cycles via a galvanostatic charge–discharge test.