Thermodynamics of hydrogen release from the molecular BNC compounds: A computational study

Boron-nitrogen hydride (BNHx) materials display favorable gravimetric and volumetric densities of hydrogen. The hydrogen release is, however, too exothermic for direct practical applications and/or on-board regeneration. Different approaches aiming at improved thermodynamics are being pursued. In the past we suggested that the (BNHx) compounds infused in nanoporous silica undergo dehydrogenation reactions with more favourable thermodynamics than the neat (BNHx) compounds. Here we present results for molecular systems, in which the (BNHx) compounds are chemically modified. We recognize that the dehydrogenation of cylohexane is endothermic while the dehydrogenation of perhydroborazine, which is a BN analog of cyclohexane, is exothermic. Next, we recognize that the BN unit is isoelectronic with the CC unit. Finally we propose that ByNyCz compounds might display thermodynamics for dehydrogenation intermediate between this for carbon based and that for BN based hydrides. The thermodynamics of dehydrogenation calculated for molecular, cyclic carbon-, BN-, and BNC- based hydrides confirms this hypothesis. The calculations were performed at the density functional level of theory with a hybrid B3LYP exchange-correlation functional.