LAUSR

Abstract This research demonstrated the annealing-free synthesis of K-doped mixed-phase TiO 2 (anatase and rutile, AR) nanofibers (K-TNF) on Ti foil at 150 °C assisted by KOH (aq.) for electrochemical supercapacitors (ESCs) applications. The aggregated network and the average diameter of K-TNF was slightly decreased with the increase of KOH (aq.) concentrations from 4 to 6 M, while the amount of K-doping, Ti 3+ interstitials, and OH functional groups was substantially increased. The TiO 2 phase was entirely rutile at 4 M KOH (aq.) , while it was a mixed AR phase at 5 and 6 M. All the K-TNF modified Ti electrodes (K-TNF/Ti) exhibited quasi-rectangular shaped cyclic voltammograms (CVs) in a wide potential range and the specific capacitance (C s ) for the optimal electrode with mixed AR phase TiO 2 was ca. 102.12 and 97.30 mF/cm 2 , obtained from the CV (scan rate, 5 mV/s) and charge-discharge (CD, current density, 50 μA/cm 2 ) measurements, respectively. The higher C s for the optimal K-TNF/Ti electrode can be ascribed to the synergistic effect of mixed AR phase, high percentage of K-doping ( ca. 17.20%), and Ti 3+ interstitials ( ca. 16.20%), respectively. The directional electron transport through the 1D channel as well as the OH functional groups on the K-TNF surface is also contribute to enhance C s . The K-TNF/Ti electrode is covered excellent stability with the C s retention of ca. 91% and a very small change of internal series resistance (R s ) and charge transfer resistance (R ct ) at the electrodeǀelectrolyte interface after 2500-CD cycles.