Herein, 3D in-situ hollow carbon fiber/carbon nanosheet/Fe3C@Fe3O4 (h-CNF/CNS/Fe3C@Fe3O4) was constructed using ferrocene and oleic acid by a solventless one-step process that did not require additional filtering, neutralization, drying, or calcination steps. The iron-oleate chelating structure that self-assembled during annealing facilitated the fabrication of 3D in-situ h-CNF/CNS/Fe3C@Fe3O4 by undergoing graphitization at 600 degrees C. This carbon shell of the 3D in-situ h-CNF/CNS/Fe3C@Fe3O4 was derived from the two cyclopentadienyl rings in ferrocene. This hybrid material made from economically cheap oleic acid exhibited superior supercapacitive behavior: high specific capacitance of 327 F g(-1) at 5 mV s(-1) and 210 F g(-1) at 10 mV s(-1), good rate capability of 60 F g(-1) at 10 A g(-1) (compared to 70 F g(-1) at 1 A g(-1) for pure Fe3O4),and superior retention of 108% after 6000 cycles at 100 mV s(-1). These superior supercapacitive properties were ascribed to the 3D graphitic h-CNF/CNS for enhancing electrical conductivity and the carbonaceous shell over Fe3C@Fe3O4 core for buffering the bulk expansion of ironrelated particles. (C) 2017 Elsevier Ltd. All rights reserved.