Molecular Modeling of Cu-, Ag-, and Au-Decorated Aluminum Nitride Nanotubes for Hydrogen Storage Application

Abstract

The stabilities, electronic properties, and reactivities of hydrogen interactions with Cu-, Ag-, and Au-decorated aluminum nanotubes (AlNNT), H2-AlNNT, H2-Ag@AlNNT, H2-Au@AlNN T, and H2-Cu@AlNNT, for efficient hydrogen storage were investigated using density functional theory (DFT) computations at the ωB97XD/def2svp level of theory. The electron shared by H2-Ag@AlNNT, H2-Au@AlNNT, and H2-Cu@AlNNT, as well as the chemical bond created with the adsorbed hydrogen molecule, indicate chemisorption from the electron localization function (ELF) analysis, which is compatible with the adsorption energies obtained. H2-Cu@AlNNT exhibited molecular physisorption with an average hydrogen adsorption energy (Eads) of −0.027 eV, whereas H2-AlNNT, H2-Ag@AlNNT, and H2-Au@AlNNT exhibited chemisorption behavior. The molecular adsorption energies for H2-Ag@AlNNT and H2-Au@AlNNT were, respectively, −0.136 and −0.081 eV. Thus, in comparison to the other H2-adsorbed systems under investigation, the highest obtained adsorption energies were observed for these two decorated nanotube systems, respectively. H2-Ag@AlNNT and H2-Au@AlNNT are, therefore, better when compared to the other studied materials in terms of storage and adsorption of hydrogen molecules. Additionally, the negative value of Eads shows that the stated hydrogen molecule’s adsorption is thermodynamically efficient. Also, in comparison with the Department of Energy (DOE) standard, the calculated wt % values for the studied systems were found to be 6.0 and 5.8 wt % for the AlNNT and metal-decorated systems, respectively. This is quite lower than the recommended standard; however, adsorption of more hydrogen molecules and surface engineering could improve the obtained wt %. The desorption temperature was also found to be within the required range for storage materials, according to DOE. Ab initio molecular dynamics simulation also confirms surface stability. Correspondingly, the NCI analysis reveals that the nature of the connection is linked to van der Waals forces and that the hydrogen molecule interacts well with the adsorbent surfaces. These phenomenal results enshrined probably the noble metal-decorated AlN nanotube materials as efficient reservoir materials for hydrogen storage.