Mo2N-Activated Metal Borohydride Nanocomposites for H2 Storage

Metal hydrides play a pivotal role in advancing the hydrogen economy by providing a compact solution for onboard hydrogen storage. However, their practical application is hindered by undesirable side reactions and slow kinetics during hydrogen uptake and release. We present herein enhanced thermodynamics and kinetics of hydrogen uptake/release through the infiltration of lithium borohydride (LiBH4) into Mo2N-doped defective boron nitride (Mo2N-DBN) host. Density functional theory (DFT), Ab initio molecular dynamics (MD), and a wide array of experimental data suggested that the Mo2N-DBN host promotes proximity between the active sites of LiBH4, effectively preventing aggregation during sorption processes, thereby leading to a reversible hydrogen storage capacity of 10.80 wt % at 200 °C and 50 bar for LiBH4@Mo2N-DBN composite with minimal loss after five hydrogenation-dehydrogenation cycles. This marked an 84% enhancement over pure LiBH4 under identical conditions and represented the highest reported storage capacity among LiBH4-based composites to date. The Mo2N sites in the composite prevented direct melting transitions of LiBH4 and facilitated the weakening of H-H bonds, which in turn gave rise to fast dehydrogenation kinetics (Ea = 77.44 ± 0.02 kJ/mol). Additionally, analysis of hydrogenation-dehydrogenation energetics indicated that Li atoms are drawn from the LiBH4 cluster toward Mo2N sites, coordinating with N atoms and thereby promoting better interface stability. We anticipate the continuous formation of interfaces between Mo2N-DBN, LiH, and B, where rehydrogenation reactions can proceed efficiently, supported by the migration of H-containing species between bulk and interfacial regions.