Mechanically flexible electrospun carbon nanofiber (ECNF) mats were prepared by electrospinning mixtures containing hydrothermal liquefaction (HTL) derived biochar and polyacrylonitrile (PAN) into precursor nanofiber mats followed by stabilization in air and then carbonization in argon. The resulting ECNF mats well retained the overall morphological structures of their precursors (i. e., biochar/PAN composite nanofiber mats), and the carbon nanofibers showed the enlarged specific surface area upon the increase of biochar loading amount in precursor nanofibers. The ECNFs (4/10), which were derived from composite nanofibers with the biochar/PAN weight ratio being 4/10, had the fiber diameters of similar to 350 nm and the BET specific surface area of 30.12 m(2)center dot g (1); and these ECNF mats exhibited the highest gravimetric capacitance of 37.60 F center dot g (1) at the current density of 500 mA center dot g (1). Hence, the prepared ECNF mats could potentially be utilized for energy related (e. g., supercapacitor) applications. (C) 2017 Elsevier B.V. All rights reserved.