High-Capacity Room-Temperature Hydrogen Storage in Carbon Nanotubes via Defect-Modulated Titanium Doping

Carbon materials have been at the forefront of hydrogen storage research. However, without improvements in the hydrogen binding strength, as provided by transition-metal dopants, they will not meet practical targets. We performed ab initio density functional theory simulations on titanium-atom dopants adsorbed on the native defects of an (8,0) nanotube. Adsorption on a vacancy strongly binds titanium, preventing nanoparticle coalescence (a major issue for atomic dopants). The defect-modulated Ti adsorbs five H-2 molecules with H-2 binding energies in the range from -0.2 to -0.7 eV/H-2, desirable for practical applications. Molecular dynamics simulations indicate that this complex is stable at room temperature, and simulation of a C112Ti16H160 unit cell finds that a structure with 7.1 wt % hydrogen storage is stable.