Fluorine-doped anatase for improved supercapacitor electrode

Anatase is an attractive supercapacitor material as it is widely available, non-toxic, stable over a wide potential window, and has a high theoretical value of specific capacitance, but the experimental value is still low. Here, we show that HF treatment leads to simultaneous nanostructuring and fluorine doping of anatase. Structural characterizations show a substantial reduction in the particle size and an order of magnitude increase in the surface area without any change in the distribution of the crystal facets of anatase. Material characterizations show that fluorine doping leads to the creation of oxygen vacancies as well as the Ti3+ states. Electrochemical characterizations show that these defects increase electronic charge carrier density (9×1019 cm−3) and local conductivity of the doped anatase by an order of magnitude compared to the pristine anatase (7.68×1018 cm−3). As a result of this, doped anatase shows three times (236 Fg−1) higher specific capacitance than the pristine one and its rate capability is also better. Doped anatase also has good cycling stability with a minimum decrease in the specific capacitance through 10000 charge/discharge cycles.