Two-dimensional graphitic carbon nitride (g-CN) sheet, functionalized with polylithiated molecules (CLi2, OLi2), has been investigated to study their structural, electronic and hydrogen (H-2) storage properties by van der Waals corrected first principles calculation. A strong binding of both CLi2/OLi2 with two-sided coverage and large enough molecular distance ensures their uniform dispersion over the g-CN monolayer without forming clusters. Each Li in g-CN@2CLi(2) (g-CN@2OLi(2)) adsorbs 3H(2), due to its cationic nature through transferring a portion of its charge, resulting into a high H-2 storage capacity of 10.34% (9.76%). The calculated H-2 adsorption energies are well suited for practical applications. (C) 2017 Elsevier B.V. All rights reserved.