Supercapacitors are emerging as a desirable energy storage medium in view of their order of magnitude higher power density than batteries and energy density than electronic capacitors.One of the key issues in the development of a suitable electrode material for supercapacitors is that materials showing large specific capacitance are poorly abundant. In this paper, we show that niobium doped titanium dioxide (Nb:TiO 2 ) nanowires developed by electrospinning have an order of magnitude higher capacitance (~280 Fg -1 ) than pristine TiO 2 (~40 Fg -1 ) or zirconium doped TiO 2 (~30 Fg -1 ). The cyclic voltammetry and charge discharge cycling experiments show that the Nb:TiO 2 nanowires have 100% coulombic efficiency and could be operated over 5000 cycles without any appreciable capacitance degradation. The superior charge storage capability of the Nb:TiO 2 is assigned to its high electrical conductivity as determined by electrochemical impedance spectroscopy. A practical supercapacitor is fabricated in asymmetric configuration using the Nb:TiO 2 as anode and activated carbon as cathode. The device delivered energy densities of 16.3, 11.4 and 5.6Whkg -1 at power densities of 770, 1310, and 1900 Wkg -1 , respectively. These values are much superior than a control device fabricated using activated carbon as its both electrodes. 3 compared to that of the carbons they are employed in the SCs as one of the electrodes to enhance the energy density. Such device configuration is termed as asymmetric supercapacitors (ASCs). Even if the intense research on SCs is aimed at increasing energy density similar to that of batteries, attention is equally given at lowering fabrication costs and on materials of larger abundance.High electrochemical reversibility, multiple oxidation states, large surface area, and high electrical conductivity are properties required for high performance SC electrodes.Among the TMOs, TiO 2 have relatively lower toxicity, larger abundance and lower cost, environmental friendly, and desirable optical, electrical and electrochemical properties. 8 It has been extensively studied for its wide application from catalysis to energy storage. 9,10 For its application in SCs, theoretically TiO 2 could deliver specific capacitance 700 Fg -1 (See Electronic Supplementary Information, † ESI, † S1); i.e., TiO 2 nanostructures hold good promise as a desirable SC electrode. However, its practically achieved C S is rather low thereby limiting its commercial deployability (see Table 2). We believe that this poor performance could be related to the inferior electrical conductivity of nanostructured TiO 2 (~10 -5 S/cm) 11,12 . Doping of TiO 2 with transition metals such as W +6 , Nb 5+ , V +5 , Ce +4 , Zr +4 , Fe +3 and Ni +3 or non-metals such as H and N is considered to be one of the efficient method to improve the electrical conductivity of TiO 2 . 13-16 The Nb doped TiO 2 (Nb:TiO 2 ) have three orders of magnitude higher electrical conductivity than pristine TiO 2 11,17 and show superior performance in electrochemical dev...
