By using first-principles calculations based on density functional theory, we design a potential high-capacity hydrogen storage medium by exohedrally functionalizing a stable inorganic Si20H20 nanocage with small organic molecules and Li atoms. The perhydrogenated Si20H20 nanocage was functionalized by replacing H atoms with -CN2H3 (or -CONH2) and Li atoms, and the resulting functionalized complexes show high structural stabilities. Our calculation reveals that Si20H10(CONHLi)(10), Si20H10(CONLi2)(10), Si20H10(CN2H2Li)(10), and Si20H10(CN2HLi2)(10) possess an adequate hydrogen binding energy that is suitable for practical storage and usage at ambient temperature. When these complexes reach their maximum H-2 uptake capacity, the gravimetric hydrogen percentage is 11.57 wt% for Si20H10(CONHLi)(10), 12.40 wt% for Si20H10(CONLi2)10, 10.17 wt% for Si20H10(CN2H2Li)(10), and 12.50 wt% for Si20H10(CN2HLi2)(10). These complexes can be dispersed into metal organic frameworks (MOFs) to improve their hydrogen storage properties further. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.