Hydrogen Adsorption and Dissociation Using Single Metal Atom Doped Mg12O12 Nanocage as a Catalyst: A DFT Study

Abstract

Energy is the keystone of life on Earth, powering everything from microscopic levels to large- scale chemical reactions. The expanding population and increasing industrial activities have reinforced the energy demands, traditionally sourced from fossil fuels. However, the finite nature of these resources and their detrimental environmental impacts necessitate a transition to sustainable energy solutions. Currently, hydrogen emerges as the outstanding substitute for fossil fuels, making it a more valuable energy source due to its high energy density, renewability, and clean burning nature, producing only water as a by-product. Hence, efficient hydrogen utilization requires its dissociation because molecular hydrogen is not an effective energy source as the atomic form. In this regard, hydrogen dissociation reaction on single-atom catalysts (SAC) is an essential step in sustainable and non-toxic energy production. Our study employed DFT calculations to investigate the adsorption and dissociation of molecular hydrogen on 3d transition metal atoms doped onto Mg12O12 nanocages. Each TM@Mg12O12 complex is evaluated to identify the most stable spin state for the catalytic reaction. The energetic analysis reveals that the Sc@Mg12O12 and Ti@Mg12O12 complexes exhibit high and identical interaction energy (-2.13eV) among the studied complexes. Further evaluation using NBO, FMO, IRI, and QTAIM analysis revealed the charge transfer carried from nanocage to metal and confirmed the partial covalent interactions between the TM-doped complexes. The adsorption of molecular hydrogen on the TM-doped nanocage exhibits negative adsorption energy which confirms the exothermic nature of H2 adsorption. Notably, the homolytic dissociation of H2 on the Ti@Mg12O12 complex displayed the lowest activation barrier (0.23eV), highlighting its potential as an efficient catalyst for hydrogen dissociation reactions. QTAIM of H2TM@Mg12O12 studies the interaction between the hydrogen and catalyst and confirms the covalency. NBO and EDD analysis confirm the transfer of charge from metal bonding to hydrogen antibonding orbital which leads to the dissociation of the H-H bond and facilitates the adsorption of hydrogen atoms on the catalyst. Our investigation sheds light on the factors that govern the electronic properties and catalytic ability of TM-doped Mg12O12 nanocage complexes in hydrogen dissociation reactions and paving the way for the development of improved hydrogen energy technology.