Free-standing nitrogen-doped TiO₂ nanorod arrays with enhanced capacitive capability for supercapacitors

TiO2 nanomaterials have attracted desirable attention as advanced electrode materials in supercapacitors, but they suffer from poor conductivity and low capacitance. Herein, we developed an effective approach to dramatically boost the capacitive capability of TiO2 nanorods by controlling the morphology of TiO2 and introducing N dopants upon nitridation process. The nitrided TiO2 with different morphologies are facilely synthesized by a seed-assisted hydrothermal method with different concentrations of nanosize TiO2 as seeds and subsequent nitridation. Without seeding, TiO2 nanorods are assembled into porous microflowers, while the introduction of seeds can induce the vertical growth of TiO2 nanorods. The results also show that the morphology of TiO2 can affect the doping degree of nitrogen. Owing to the improved charge transport and unique free-standing nanorod structure, the optimized nitrided TiO2 electrode obtains a remarkable areal capacitance of 177.1 mF cm(-2) at 4 mA cm(-2), which is much larger than nitrided TiO2 electrode without seeding (16 mF cm(-2)). This provides a general method for increasing the areal capacitance of nanomaterials by adjusting the seed solution concentration of the seed-assisted method.