Abstract:
Efficient and cost-effective hydrogen storage remains a significant challenge for utilization
of hydrogen as a fuel source. In response, the search for new chemical hydrides has become
a major focus. Molecular complexes such as ammine boranes serve as promising hydrogen
storage materials, releasing multiple equivalents of molecular hydrogen (H₂) upon
decomposition. In this work, a detailed theoretical analysis of aromatic thiomorpholine
borane (ATMB), a cyclic amine-borane, was conducted to assess its potential as a hydrogen
storage material. Thermochemical parameters, B-N bond dissociation energies and the
potential energy surface associated with dehydrogenation pathways were calculated by using
the CBS-QB3 level of theory. The computed Gibbs free energy changes indicate the
thermodynamic feasibility of hydrogen release from ATMB. Furthermore, the enthalpy of
dehydrogenation at 298 K was found to be -50.7 kJmol-1, suggesting that the hydrogen
elimination process is exothermic - a desirable feature for practical hydrogen storage
systems. Transition state structures were identified for both non-catalyzed and borane (BH3)-
catalyzed dehydrogenation pathways. The results show that BH3 significantly lowers the
activation barrier to 41 kJmol-1.This value is much lower than the B-N bond dissociation
energy of 94 kJmol-1. Therefore, BH3 plays an essential catalytic role in facilitating hydrogen
release. This study represents the first theoretical investigation of ATMB as a hydrogen
storage candidate and provides valuable insights into the design and development of efficient
hydrogen storage materials.
