Hydrogen storage in TiO2 functionalized (10, 10) single walled carbon nanotube (SWCNT) – First principles study

• Theoretical study of hydrogenation in TiO2 functionalized SWCNT is done.
• Binding energy of H2 to the composite system is in ideal range (0.10–0.39 eV).
• H2 storage capacity is high (6.6 wt.%) due to non-clustering of TiO2 molecules.
• Functionalization leads to transformation of metallic tube to semiconductor.
• The study gives much hope for using CNT as a practical hydrogen storage medium.

Hydrogen storage in titanium dioxide (TiO2) functionalized (10, 10) armchair single walled carbon nanotube (SWCNT) is investigated through first principle calculations using density functional theory (DFT). This first principles study uses Vienna Ab-initio Simulation Package (VASP) with ultrasoft pseudopotentials and local density approximation (LDA). The necessary benchmark and other systematic calculations were carried out to project the hydrogen storage capability of the designed system. Interestingly, the TiO2 molecules functionalized on the outer surface of SWCNT do not undergo any dimerization/clustering thus giving excellent stability and usable gravimetric hydrogen storage capacity of 5.7 wt.% and the value nearly fulfills the US DOE target (i.e. 6 wt.%). The band structure and density of states (DOS) plots suggest that the functionalization can lead a way to transform the nature (metallic → semiconducting) of the pristine SWCNT. The nominal values of H2 storage capacity and binding energies give much hope for using CNT functionalized with TiO2 as a practical and reversible hydrogen storage medium (HSM).