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Graphene-based nanocomposites are regarded as potential candidate for hydrogen storage. In this work, the energetics of the hydrogen adsorption on graphene with TiO2 decoration is systematically investigated based on first-principles total energy calculations. TiO2 cluster is chemisorbed on graphene via O-C bonds. The C atoms near TiO2 cluster act as the nucleation positions for the hydrogen atom adsorption, and the binding energy of hydrogen atoms on graphene is significantly enhanced due to the decoration of TiO2 clusters, which is larger than the binding energy of hydrogen atoms in hydrogen molecules. It can be deduced that the hydrogen storage capacity could reach 7.3 wt. %, provided that the content of TiO2 in graphene is 5 wt. %. The results give a comprehensive understanding on electrochemical hydrogen storage behavior of graphene-based nanocomposites. [ABSTRACT FROM AUTHOR]