Development of the ReaxFFCBN reactive force field for the improved design of liquid CBN hydrogen storage materials

Abstract

Liquid CBN (carbon–boron–nitrogen) hydrogen-storage materials such as 3-methyl-1,2-BN-cyclopentane have the advantage of being easily accessible for use in current liquid-fuel infrastructure. To develop practical liquid CBN hydrogen-storage materials, it is of great importance to understand the reaction pathways of hydrogenation/dehydrogenation in the liquid phase, which are difficult to discover by experimental methods. Herein, we developed a reactive force field (ReaxFF_CBN) from quantum mechanical (QM) calculations based on density functional theory for the storage of hydrogen in BN-substituted cyclic hydrocarbon materials. The developed ReaxFF_CBN provides similar dehydrogenation pathways and energetics to those predicted by QM calculations. Moreover, molecular dynamics (MD) simulations with the developed ReaxFF_CBN can predict the stability and dehydrogenation behavior of various liquid CBN hydrogen-storage materials. Our simulations reveal that a unimolecular dehydrogenation mechanism is preferred in liquid CBN hydrogen-storage materials. However, as the temperature in the simulation increases, the contribution of a bimolecular dehydrogenation mechanism also increases. Moreover, our ReaxFF MD simulations show that in terms of thermal stability and dehydrogenation kinetics, liquid CBN materials with a hexagonal structure are more suitable materials than those with a pentagonal structure. We expect that the developed ReaxFF_CBN could be a useful protocol in developing novel liquid CBN hydrogen-storage materials.