Exploring the Hydrogen Storage Potential of Allylamine Borane Using Density Functional Theory

Abstract This study focused on investigating the potential of allylamine borane (AABH 3 ) as a hydrogen‐releasing compound and its viability as an alternative energy source. The investigation involved a comprehensive analysis of its structure and thermochemistry during the dehydrogenation process using density functional theory (DFT) methods. The structural parameters computed with the M06‐2X method were observed to be closer to the experimental values than those of B3LYP and wB97XD3, particularly, the bond lengths. The C−N−B bond angle was observed to increase with dehydrogenation, and higher with doubly dehydrogenated adduct. Also, the dihedral angle was observed to change from negative to positive and back to negative in AABH 3 , AABH 2 and AABH respectively. The reaction enthalpy (▵ H r ) for the first dehydrogenation step obtained at M06‐2X/cc‐pVTZ level is exothermic (−19.6 kJ/mol), while the second step is endothermic (132.6 kJ/mol). However, the values of the entropy in the first and second dehydrogenation steps are 122.0 and 124.0 kJ/mol respectively, indicating the feasibility of the reaction. The values of the reaction free energy (▵ G r ), in the first and second steps were calculated to be −56.0 kJ/mol and 95.7 kJ/mol respectively, indicating that the second step of the reaction is rate limiting. The relative free energies of the reaction also corroborated this observation. The mechanism of the reaction was observed to be initiated by the abstraction of AABH 3 proton by the BH 3 , over a distance of 1.37 Å. Importantly, the calculated dehydrogenation reaction energies demonstrated minimal energy requirements for the hydrogen release reactions, indicating the suitability of allylamine borane for chemical hydrogen storage onboard various applications.