Template-free two-dimensional (2D) titania/titanate nanosheets on Ti metal foil (TiNS/Ti) is prepared by a hydrothermal method at 150 degrees C assisted by KOH(aq.), followed by sintering at 500 degrees C. A single thin layer of TiNS is grown with 2D morphology when using low concentrations of KOH(aq.) (0.25 and 0.5 M). However, the morphology is transformed to 1D when using a high concentration of KOH(aq.). The TiNS is a mixture of rutile TiO2 and K-titanate (K2Ti3O7 and K2Ti2O5) with the formation of Ti3+ interstitials. The optimized TiNS/Ti electrode exhibits quasi-rectangular cyclic voltammograms (CVs) in a wide potential range. The specific capacitance (C-s) are 6.8 x 10(3) and 4.7 x 10(3) mu F/cm(2) according to the CV (scan rate, 5 mV/s) and charge-discharge measurements (CD, current density, 50 mu A/cm(2)), respectively. These values are much higher than those reported for pure OD and 1D TiO2 nanostructures.The higher C-s for the TiNS/Ti electrode can be ascribed to the increased rate of K+ intercalation and de-intercalation during charging and discharging, as well as enhanced conductivity enable by the K in the crystal lattice (10.30%) and Ti3+ interstitials (5.2%), respectively. The TiNS/Ti electrode shows excellent stability with the C-s retention of 89% even after 5000 CD cycles.