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.
