Synthesis of mesoporous spherical TiO₂ and its application in negative electrode of hybrid supercapacitor

To fabricate a hybrid supercapacitor comprising activated carbon and TiO₂ electrodes, anatase TiO₂ was investigated as a candidate negative electrode material. It was synthesized by a combination of the sol-gel and microwave methods using dodecylamine as a structure directing agent. The synthesized TiO₂ had uniform size (~400 nm), a spherical morphology, a mesoporous structure (specific surface area = ~100 m²g^-1, pore size distribution = ~10 nm), and anatase phase without any impurities. To balance the power and energy densities of positive (activated carbon) and negative electrodes (TiO₂), each electrode was confirmed to have the specific capacity of about 190 mAh g^-1 and 50 mAh g^-1 (at 1 C-rate = 250 mA g^-1) through half cell tests. While the specific capacitance (23 F cm^-3) of the hybrid supercapacitor achieved about 28% increase compared to an existing supercapacitor (electric double-layer capacitor = 18 F cm^-3) at a current density of 0.5 mA cm^-2, it had a low retention ratio of 91% during 100 cycles due to the poor electronic conductivity of TiO₂. However, it was confirmed that anatase TiO₂ is suitable for use as a negative material in hybrid supercapacitors.