Activated porous carbon nanofibers (CNFs) with three different types of porous structures, which were controlled to contain 1, 4, and 8 wt% of Sn-poly(vinylpyrrolidone) (PVP) precursors in the core region and 7 wt% polyaniline (PAN)-PVP precursors in the shell region during electrospinning, were synthesized using a co-electrospinning technique with H-2-reduction. The formation mechanisms of activated porous CNF electrodes with the three different types of samples were demonstrated. The activated porous CNFs, for use as electrodes in high-performance electrochemical capacitors, have excellent capacitances (289.0 F/g at 10 mV/s), superior cycling stability, and high energy densities; these values are much better than those of the conventional CNFs. The improved capacitances of the activated porous CNFs are explained by the synergistic effect of the improved porous structures in the CNF electrodes and the formation of activated states on the CNF surfaces. (C) 2013 Elsevier Ltd. All rights reserved.