Accentuating the Competency of $3d$ Transition Metal Doped $Mg_4$ Clusters towards Molecular Hydrogen Adsorption: A DFT Study

TL;DR

This study uses DFT calculations to show that doping Mg4 clusters with 3d transition metals enhances their ability to adsorb molecular hydrogen, with specific metals like Ni and Fe providing higher binding energies and storage capacities.

Contribution

It reveals how 3d transition metal doping alters hydrogen adsorption properties of Mg4 clusters, identifying optimal metals and geometries for improved hydrogen storage.

Findings

NiMg3 adsorbs up to 13.28 wt% H2

FeMg3+ adsorbs up to 7.89 wt% H2

Doping with 3d TM enhances hydrogen binding energies

Abstract

Density functional theory $(DFT)$ studies show that doping of $3d TM$ atoms into $Mg_4^{0,+} (TMMg_3^{0,+})$ can alter the endothermic nature of molecular hydrogen adsorption on bare $Mg_4^{0,+}$. $H_2$ adsorption on $TMMg_3^{0,+}$ clusters depends on the $TM(3d)$ orbital contribution to the frontier molecular orbitals of the clusters. In $H_2TMMg_3^{0,+}$ complexes, $H_2$ is adsorbed through donation and back donation of electronic charges with $TMMg_3^{0,+}$ clusters. $H_2$ binding energy is the maximum for $NiMg_3$ (-0.76 eV) and $FeMg_3^+$ (-0.48 eV) among the neutral and cationic $TMMg_3$ clusters, respectively. The geometry of $H_2$ adsorption complex entirely depends on the geometry of the host cluster. The lowest energy symmetrical structures of both $NiMg_3$ and $FeMg_3^+$ clusters are less efficient than some slightly higher energy low symmetrical geometrical isomers for adsorption of multiple hydrogen molecules (13.28 $H_2$ $wt\%$ for $NiMg_3$ and 7.89 $H_2$ $wt\%$ for $FeMg_3^+$). Greater exposer of $TM^{0,+}$ along with its lower Mg coordination number make host clusters more suitable for hydrogen storage.