First-principles study on hydrogen storage by graphitic carbon nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the hydrogen storage capacity of graphitic carbon nitride nanotubes. Graphitic carbon nitride nanotubes could be attractive hydrogen sorbent for two reasons: firstly, its porous structure allows easy access of hydrogen into the interior of the nanotubes; and secondly, the doubly bonded nitrogen at its pore edges provides active sites for either the adsorption of hydrogen (chemically and physically), or functionalization with metal catalysts. Our calculations show that an isolated nanotube can uptake up to 4.66 wt. % hydrogen, with an average overall hydrogen adsorption energy of about −0.22 eV per H atom. In the form of a bulk bundle, the hydrogen storage capacity is enhanced due to the increased availability of space among the tubes. We predict that the hydrogen storage capacity in the bundle is at least 5.45 wt. %. Importantly, hydrogen molecules can easily access the tube’s interior due to the low energy barrier (∼0.54 eV) for their passage through the pores, indicating a fast uptake rate at relatively low pressure and temperature. Our findings show that graphitic carbon nitride nanotubes should be applicable to practical hydrogen storage because of the high gravimetric capacity and fast uptake rate.