Coordination of nickel atoms with Al12X12 (X = N, P) nanocages enhances H2 adsorption: A surface study by DFT

• Decoration of nickel on Al12X12 (X = N, P) nano-cages provides four distinct geometries.
• H2 adsorption on pristine Al12X12 (X = N, P) nano-cages is really low.
• Decorated nickel at Ni-Al12X12 (X = N, P) nano-cages increases H2 adsorption significantly.
• Adsorbed nickel changes HOMO and LUMO distributions of Al12X12 (X = N, P), drastically.

Density functional theory (DFT) calculations have been performed to study the adsorption of hydrogen on the surface of pristine and nickel decorated Al12N12 and Al12P12 nano-cages. Decoration of nickel on the surface of nano-cages delivers four distinct geometries. Hydrogen adsorption is studied on the surface of Ni-decorated Al12X12 (X = N, P) in these four geometries (named as P1, P2, P3, and P4). Calculations reveal very weak physisorption of H2 on pristine nano-cages while significant enhancement in its adsorption properties is found upon using Ni-X12Y12 nano-cages. The hydrogen adsorption on Ni-Al12N12 nano-cage is in order of P2 > P3 > P4 > P1, whereas the order of adsorption energies on Ni-Al12P12 is P2 > P1 > P3 > P4. Ni complexation with Al12N12 shows considerably higher potential for H2 adsorption compared to Al12P12. We used natural bond orbital (NBO), molecular dipole moment, density of states (DOS) and frontier molecular orbitals analyses to observe the changes in the electronic structure of Ni-Al12X12 nano-cages on adsorption of H2.