RuO2-containing activated carbon nanofibers with hollow cores (PMRu-ACNEs) are prepared through one-step electrospinning using polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), and ruthenium(III) acetylacetonate followed by thermal treatment. The porous PMRu-ACNE composites exhibit an improved morphological structure and textual properties due to the increased surface area, unique nanotexture, and presence of several functional groups such RuO2 in the ACNFs. Electrochemical measurements of PMRu-ACNF reveal a maximum specific capacitance of 180 Fg(-1) and high energy densities of 20-14 Whkg(-1) in the power density range of 400 to 10,000 W kg(-1) in aqueous KOH electrolyte. In contrast, the ACNF electrodes show a lower specific capacitance and the energy density rapidly drops to 2 Whkg(-1) at power densities of 4,000 Wkg(-1). Therefore, the PMRu-ACNE composite electrodes may be more suitable as supercapacitors than regular ACNFs are, due to the synergistic effect between the electric double-layer capacitance of porous ACNFs and the pseudocapacitance of Ru02. (C) 2015 Elsevier Ltd. All rights reserved.