Surface functionalization-enhanced spillover effect on hydrogen storage behaviors of Ni-B nanoalloy-doped activated carbon is investigated in comparison to the 3D graphene-based material. It is discovered that the hydrogen storage capacity of the activated carbon increases from Ni-B nanoalloy-doping but much less than that of graphene. After surface functionalization, although the specific surface area and micropore volume of the doped activated carbon decrease significantly, a hydrogen storage capacity is still almost as same as that of the unfunctionalized larger surface one, while showing a large desorption hysteresis. We argue that the surface functionalization greatly enhances the spillover process on carbon based adsorbents, thus playing an essential role in hydrogen storage capacity improvement. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.