High-capacity reversible hydrogen storage in Na-decorated Al-N-O nanocluster: a DFT-D3 study

Efficient and reversible hydrogen storage remains a major challenge for clean energy technologies. Here, DFT-D3 calculations combined with PDOS, TD-DFT, QTAIM, and RDG analyses were used to evaluate a Na-decorated Al₄N₄O₂ nanocluster as a solid-state hydrogen storage material. The optimized Al-N-O framework is structurally stable, with a formation energy of - 4.645 eV, and shows strong electronic polarization due to charge redistribution between Na and O/N sites. Ab initio molecular dynamics simulations at 600 K predict high thermal stability of the Al₄N₄O₂Na₄ nanocluster during the simulated hydrogen adsorption-desorption process. The resulting electropositive Na and electron-rich O/N regions create dual adsorption sites that promote polarization-induced physisorption of H₂. Upon successive hydrogenation, adsorption energies range from - 0.470 to - 0.309 eV per H₂, with desorption enthalpies of - 28.56 to - 21.45 kJ mol^-1 per H₂, suggesting reversible hydrogen release at 244-347 K. The predicted gravimetric capacity reaches 20.13 wt%, exceeding the DOE 2025 target.