Surface-Engineered TiO₂ for High-Performance Flexible Supercapacitor Applications

Titanium dioxide (TiO₂) shows excellent pseudocapacitive properties. However, the low internal conductivity of TiO₂ limits its use in supercapacitor applications. Therefore, an efficient surface engineering process was developed to enhance the overall pseudocapacitive performance of rutile TiO₂ nanorods. Specifically, surface-engineered TiO₂ nanorod arrays coordinated on carbon cloth were established through the Kapton tape-assisted hydrothermal route. X-ray diffraction analysis confirmed the formation of a tetragonal TiO₂ rutile phase. Morphological analysis revealed the formation of uniform nanorods with an apparent high surface-to-volume aspect ratio. X-ray photoelectron spectroscopy analysis showed that the TiO₂ synthesized in the presence of Kapton tape and annealed under air had high content of hydroxyl groups and Ti³⁺, which is favorable for supercapacitor performance. Surface treatment of the samples led to significantly enhanced conductivity and electrochemical behavior of TiO₂. The surface-engineered TiO₂ nanorod arrays show specific capacitance of about 57.62 mF/cm² at 10 mV/s in 2 M KOH, with excellent rate capability of about 83% at 200 mV/s, and also exhibit long cycle life, retaining 91% of their original capacitance after 10,000 charge/discharge cycles, which is among the highest values reported for TiO₂-based supercapacitors. Graphical Abstract: [Figure not available: see fulltext.]