We identified several parameters that correlate with the hydrogen physisorption energy and physicochemical properties of heteronuclear bonding in single-walled carbon nanotubes (SWCNT) and graphene. These parameters were used to find the most promising heteronuclear doping agents for SWCNTs and graphene for enhanced hydrogen storage capacity. Si-doping was showed to increase the amount of physisorbed hydrogen on such surfaces. Grand Canonical Ensemble Monte Carlo (GCMC) simulations showed that the hydrogen storage capacity of 10 at% Si-doped SwCNT (Si-CNT10) could reach a maximum of 2.5 wt%, almost twice the storage capacity of undoped SWCNTs, which were showed to reach a maximum capacity of 1.4 wt% at room temperature. To achieve this capacity, debundling effects of the uneven surfaces of Si-doped SWCNTs were found to be necessary. Similarly, 10 at% Si-doping on graphene (Si-GR10) was showed to increase the hydrogen storage capacity from 0.8 to 2.4 wt%. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.