Theoretical studies on hydrogen adsorption properties of lithium decorated diborene (B_2H_4Li_2) and diboryne (B_2H_2Li_2)

摘要

Using ab initio based quantum chemical calculations, we have studied the structure, stability and hydrogen adsorption properties of different boron hydrides decorated with lithium, examples of the corresponding anions being dihydrodiborate dianion, B_2H_2 and tetrahydrodiborate dianion, B_2H_4 which can be considered to be analogues and isoelec-tronic to acetylene (C_2H_2) and ethelene (C_2H_4) respectively. It is shown that there exists a B-B double bond in B_2H_4Li_2 and a B-B triple bond in B_2H_2Li_2. In both the complexes, the lithium sites are found to be cationic in nature and the calculated lithium ion binding energies are found to be very high. The cationic sites in these complexes are found to interact with molecular hydrogen through ion-quadrupole and ion-induced dipole interactions. In both the complexes, each lithium site is found to bind a maximum of three hydrogen molecules which corresponds to a gravimetric density of ～23 wt% in B_2H_4Li_2 and ～24 wt% in B_2H_2Li_2. We have also studied the hydrogen adsorption in a model one-dimensional nanowire with C_6H_4B_2Li_2 as the repeating unit and found that it can adsorb hydrogen to the extent 9.68 wt% and the adsorption energy is found to be -2.34 kcal/mol per molecular hydrogen.