A computational study of hydrogen adsorption on penta-NiN2 sheet and nanotubes

Stimulated by the recent synthesis of penta-NiN2 sheet [ACS Nano 2021, 15, 13,539], we study the hydrogen adsorption on the sheet and the derived nanotubes by using density functional theory with the correction of van der Waals interactions. We have found that each Ni site can only adsorb two hydrogen molecules as expected from the 18-electron rule, the corresponding capacity is 4.44 wt%. As more H2 molecules are introduced, H2 can only be very weakly adsorbed on N sites. When the sheet is curved into nanotubes, the Ni–N distance is enlarged due to the stress, which weakens the orbital hybridizations between Ni and N, and reduces the charge transfer from Ni to N. The Ni ion with a less charge on the tube shows weak polarizing ability for H2 molecule.