Porous. carbon nanofibers with Si-O-C/Si-O-Si group (Si/ACNF) mats are produced by incorporating tetraethyl orthosilicate (TEOS) into polyacrylonitrile (PAN) via electrospinning/activation, and their electrochemical properties as a supercapacitor electrode are investigated. The Si/ACNF exhibits a high surface area of up to 1386.91 m(2) g(-1) as result of the ultramicropore size distributions centered at approximately 0.8 nm and mesopore volume fraction up to 38%. The gravimetric capacitance of the Si/ACNF webs in an organic electrolyte is 91.95 F g(-1), and the energy densities are 59.72-88.23 Wh kg(-1) over the power density range of 1000-20,000W kg(-1). The electrochemical capacitance of a Si/ACNF electrode is closely related to the pore size distribution, surface area, and ionic accessibility of the electrode material, providing a large charge capacity and high rate capability. (C) 2013 Elsevier B.V. All rights reserved.