Assessing the performance of screw deformed nanotube as potential hydrogen storage material

• Hydrogen storage reactions of screw deformed carbon nanotube.
• Physisorption and thermodynamic characterization.
• The free energies and enthalpies meet the ultimate targets of DOE.
• Surface coverage and (direct/inverse) rate constant ratios are estimated.
• More promising thermodynamics are assigned to the screw deformed nanotube.

The hydrogen storage of screw deformed Ti-functionalized (5,2) single walled carbon nanotube is investigated by using the state of the art density functional theory calculations. The single Ti atom prefers to bind at the hollow site of the hexagonal ring with average adsorption energies per hydrogen molecule −0.56 and −0.52 eV for the un-deformed CNT-φ = 0 and deformed CNT-φ = 5 nanotubes, respectively. The hydrogen storage reactions 4H2 + Ti-CNT-φ = 0,5 are characterized in terms of projected densities of states and statistical thermodynamics. The free energies and enthalpies meet the ultimate targets of the department of energy for minimal and maximal temperatures and pressures. The closest reactions to zero free energy exhibit surface coverage values 0.951 and 0.816 as well as (direct/inverse) rate constant ratios 6.55 and 1.5. The translational term is found to exact a dominant effect on the total entropy change with temperature, and the more promising thermodynamics are assigned to the screw deformed nanotube.