Supercapacitors are efficient energy storage devices with long lifetime and safe service. Their effectiveness, to a big extent, is dependent on electrode materials used for accumulation of energy in form of electrostatic charges. Over the last decades, variety of carbonaceous electrode materials has been used in supercapacitors. Mostly the production of such electrodes is still oriented on unsustainable fossil fuels as precursors instead of sustainable renewable resources. In this study, freestanding carbonaceous electrode materials for supercapacitors were derived from cellulose, the most abundant renewable resource. They were synthesized via carbonization of fibrillar cellulose impregnated with CNTs (carbon nanotubes). The ensuing composite materials consisted of a CNF (carbon nanofiber) scaffold (fiber diameter in the range of 50-250 nm) covered with layers of CNTs (tube diameter in the range of 1-20 nm). Moreover, these composites were tested as electrode materials for supercapacitors. Incorporation of the CNTs into the CNFs improved electrical conductivity and also increased the surface area of the produced composite materials, which led to high specific capacitance values (up to 241 F g(-1)), cyclic stability, and power density of these materials in electrochemical measurements. These results suggest that cellulose-derived original CNF/CNT composites are sustainable and efficient carbonaceous electrodes for supercapacitors. (C) 2015 Elsevier Ltd. All rights reserved.