The generalized gradient approximation (GGA) to density functional theory (DFT) calculations indicate that the highly localized states derived from the defects of nitrogen doped carbon nanotube with divacancy (4ND-CNxNT) contribute to strong Sc and Ti bindings, which prevent metal aggregation. Comparison of the H2 adsorption capability of Sc over Ti-decorated 4ND-CNxNT shows that Ti cannot be used for reversible H2 storage due to its inherent high adsorption energy. The Sc/4ND-CNxNT possesses favorable adsorption and consecutive adsorption energy at the local-density approximation (LDA) and GGA level. Molecular dynamics (MD) study confirmed that the interaction between molecular hydrogen and 4ND-CNxNT decorated with scandium is indeed favorable. Simulations indicate that the total amount of adsorption is directly related to the operating temperature and pressure. The number of absorbed hydrogen molecules almost logarithmically increases as the pressure increases at a given temperature. The total excess adsorption of hydrogen on the (Sc/4ND)10-CNxNT arrays at 300 K is within the range set by the department of energy (DOE) with a value of at least 5.85 wt%.

This study addresses the inherent difficulty in synthesizing single-walled carbon nanotubes (SWCNTs) with uniform chirality and well-defined electronic properties through the introduction of dopants, topological defects, and intercalation of metals. Depending on the desired application, one can modify the electronic and magnetic properties of SWCNTs through an appropriate introduction of imperfections. This scheme broadens the application areas of SWCNTs. Under this motivation, we present our ongoing investigations of the following models: (i) (10, 0) and (5, 5) SWCNT doped with nitrogen (CNxNT), (ii) (10, 0) and (5, 5) SWCNT with pyridine-like defects (3NV-CNxNT), (iii) (10, 0) SWCNT with porphyrine-like defects (4ND-CNxNT). Models (ii) and (iii) were chemically functionalized with 14 transition metals (TMs): Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt and Au. Using the spin-unrestricted density functional theory (DFT), stable configurations, deformations, formation and binding energies, the effects of the doping concentration of nitrogen, pyridine-like and porphyrine-like defects on the electronic properties were all examined. Results reveal that the electronic properties of SWCNTs show strong dependence on the concentration and configuration of nitrogen impurities, its defects, and the TMs adsorbed.

Structures and electronic properties of zigzag graphene nanoribbon (ZGNR) with pyridine (3NV-ZGNR) functionalized by Scandium (Sc) at the edge were studied through quantum chemical calculations in the formalism of density-functional theory (DFT). Pyridine-like nitrogen defects is very crucial for enhancing the Sc atom binding to the defects and is thermodynamically favoured. During Sc decoration of ZGNR there is a shift from 0.35 eV small gap semiconductor regime to that of a metal which can be used for band gap tuning by controlled saturation of Sc. ZGNR decorated with Sc can attract H 2. Upon saturation of multiple H 2 in quasi-molecular fashion, the metallic character is converted to semiconductors of small gap of 0.10 eV, which are predicted to be interesting materials not only for hydrogen storage but also for their band gap engineered properties.