The novel technique of centrifuged-electrospinning is employed to fabricate immiscible polyacrylonitrile (PAN)/polymethyl methacrylate (PMMA) polymer fibers, followed by carbonization to form ultra-thin carbon nanofibers (UT-CNF) with 28 +/- 11 nm diameters. An additional centrifugal force provides a strong stretching force to stretch the dispersed droplets (PAN) into ultra-thin nanofibers, as confirmed by electron microscopy. This structure presents good electrochemical properties compared to electrospun carbon nanofibers with 126 +/- 16 nm diameters. Electrochemical impedance spectroscopy analysis shows enhanced efficient surface areas, which accumulate ions more quickly, resulting in a decrease in the charge distribution and ion diffusion resistance because the reduction in diameter provides a short pore length and large outer surface. Applied to a supercapacitor, galvanostatic charge/discharge analysis gives a maximum specific capacitance of 243 F/g at 1 A/g and capacitance retention of 77.1% at a charge/ discharge rate of 100 A/g for UT-CNF. This result is significantly higher than that of traditional electrospun carbon nanofibers. (C) 2018 Elsevier Ltd. All rights reserved.