Synthesis of carbon modified TiO2 nanotubes composite films by gas thermal penetration as symmetrical and binder-free electrochemical supercapacitor

In this work, we develop a novel carbon-modification method to improve the electronic conductivity and the electrochemical performances of TiO2 nanotubes electrodes for binder-free supercapacitor. The carbon modified TiO2 nanotubes (denoted as C-TNTs) is prepared by two-step process of anodic oxidation and gas thermal penetration method on a Ti plate. The structure and composition of C-TNTs was characterized by SEM, XRD, EDS, RAMAN, XPS and XANS, respectively. The electrochemical performances of C-TNTs were evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD) tests. The C-TNTs film presents almost the same morphology as TNTs film and C is successfully deposited on the film in different forms. The largest areal capacitance of C-TNTs film is 38.2 mF/cm2 at the scan rate of 10 mV/s in CV curves, and 12.10 mF/cm2 at the current density of 0.125 mA/cm2 in GCD measurements, 21.1 times than that of TNTs film. The great improvement of the capacitance can be attributed to the increase of conductivity and the pseudocapacitance effect, which corresponds to the C deposition and Ti4+ reduction into Ti3+, and the chemisorbed CO and OH on the film surface, respectively. The galvanostatic charging/discharging cycle test indicates the good stability and reversibility of C-TNTs film as the electrode material in the application of supercapacitor.