Ultrathin carbon layer-encapsulated TiN nanotubes array with enhanced capacitance and electrochemical stability for supercapacitors

Although titanium nitride (TiN) is promising as electrode material in supercapacitors due to the high conductivity, there are drawbacks such as the brittleness, low capacitance, and chemical stability. Herein, three-dimensional (3D) carbon-encapsulated mesoporous titanium nitride nanotubes (TiN/C NTs) arrays with carbon doping are prepared by one-step nitridation of anodic TiO₂ NTs with organic electrolyte as the carbon source. In TiN/C NTs, 3D carbon matrix not only serves as a protective layer and mechanical support to mitigate electrochemical oxidation and structural collapse, but also provides a conductive network to facilitate electron transfer. The capacitance retention of the TiN NTs electrodes increases from 72.5 to 92.2% for 4000 cycles after carbon encapsulating. Moreover, the carbon doping increases the active charge storage sites of the TiN NTs. The TiN/C NTs electrode exhibits a large volumetric capacitance of 121 F cm⁻³ (0.83 A cm⁻³), which is one time larger than that of the pure TiN NTs (69 F cm⁻³). The symmetrical all-solid-state device assembled with two TiN/C NTs electrodes and polyvinyl alcohol electrolyte shows a large volumetric capacitance of 8.3 F cm⁻³. This finding provides a good potential application in flexible supercapacitor.