Calculated properties of fully hydrogenated single layers of BN, BC2 N, and graphene: Graphane and its BN-containing analogues

Carbon is an attractive material for hydrogen adsorption due to its light weight, variety of structures, and ability to both physisorb and chemisorb hydrogen. Recently, fully hydrogenated graphene layers ("graphane") have been predicted to exist, and experimentally observed. In this work, we examine analogs of graphane, in particular BNH2 and BC2 NH4. Unlike graphene, these materials have a band gap without hydrogenation. Our results indicate that the hydrogenation product of BN is metastable: the fully hydrogenated compound BNH2 is higher in energy than hexagonal BN sheets plus H2 molecules, in sharp contrast with graphane. We find that BC2 NH4 is energetically very close to hexagonal BC2 N+2 H2 molecules. Furthermore, our examination of the relative binding strengths of rows of symmetry related hydrogen atoms on BC2 NH4 shows that this compound is marginally higher in energy than BC2 NH2 plus an H2 molecule, with the hydrogen atoms in BC2 NH2 absorbed on the carbon sites. These remaining hydrogen atoms are not as strongly bound as in graphane, indicating that the average hydrogen chemisorption energy is controllable by changing the carbon content in the B-C-N layer.