Calculated properties of fully hydrogenated single layers of BN, BC2N, 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 [J. O. Sofo , Phys. Rev. B 75, 15340 (2007)], and experimentally observed [D. C. Elias , Science 323, 610 (2009)]. In this work, we examine analogs of graphane, in particular BNH2 and BC2NH4. 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 H-2 molecules, in sharp contrast with graphane. We find that BC2NH4 is energetically very close to hexagonal BC2N+2H(2) molecules. Furthermore, our examination of the relative binding strengths of rows of symmetry related hydrogen atoms on BC2NH4 shows that this compound is marginally higher in energy than BC2NH2 plus an H-2 molecule, with the hydrogen atoms in BC2NH2 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.