This paper addresses the preparation of three-dimensional functionalized carbon felts (CFs), which were coated with nickel (Ni) nanostructures and used as an electrocatalyst for glycerol electrooxidation in alkaline medium. The commercial CFs (3D-carbon fibers) were first functionalized with O- and S- like functionalities via electrochemical pretreatment in NaOH and H2SO4, then the impacts of this pretreatment on the electrodeposited Ni nanoparticles (NiNPs) morphology, distribution, structure and performance for glycerol electrooxidation was investigated. X-ray diffraction (XRD) together with cyclic voltammetry (CV) techniques were used to detect the changes of the electrodeposited Ni oxide phases. Contact angle was used to determine impact of pretreatment on the wettability of CF. X-ray photoelectron spectroscopy (XPS) was used to get information about the added functional groups while scanning electron microscope (SEM) was used to observe the changes of NiNPs morphology, distribution, and particle size. As-synthesized NiNPs modified functionalized CFs exhibited an excellent activity concurrent with good stability for glycerol electrooxidation. The pretreatment of CF in either NaOH or H2SO4 resulted in a significant increase in the Ni surface active sites and improved their electrocatalytic activity for glycerol electrooxidation. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.