Enhanced reversibility of fluorine substituted bis-BN cyclohexane for hydrogen storage: A first-principles approach

Abstract

Liquid organic hydrogen carrier (LOHC) technology, in which hydrogen is captured in a liquid-phase compound, is a key enabler in realizing hydrogen economy. Among the LOHC materials, bis-BN cyclohexane is thermodynamically stable at 150°C and does not release detectable volatile contaminants during catalytic dehydrogenation at room temperature. In this study, we identified other potential bis-BN cyclohexane-based hydrogen storage materials with improved dehydrogenation efficiency and reversibility using density functional theory (DFT) calculations. The dehydrogenation mechanisms of bis-BN cyclohexane with and without functional group (F, Cl, NH2, CH3, and CN) substitutions were investigated by calculating the reaction enthalpies and free energies. With the Pt catalyst surface, F-bis-BN cyclohexane has slightly lower dehydrogenation reaction efficiency than the existing bis-BN cyclohexane; however, it was found that the efficiency of the reverse reaction of hydrogenation is significantly improved owing to the F substitution in bis-BN cyclohexane. Therefore, F-bis-BN cyclohexane can exhibit enhanced reversible dehydrogenation–hydrogenation cycles in the presence of a Pt catalyst and is expected to be suitable as an alternative hydrogen carrier. Details of dehydrogenation reaction pathways with activation energies and electronic properties of the dehydrogenation mechanisms have also been discussed herein.