Exceeding the hydrogen gravimetric capacity targets in cubic bundles of Li doped carbon nanotubes

Enhanced hydrogen adsorption is considered in 〈111〉 cubic arrangements of Li doped single walled carbon nanotubes. In particular we have considered the +Ω and +Σ cubic arrangements of (10,0) carbon nanotubes at different Li content and pressure at both cryogenic (T=100K) and room (T=300K) temperatures. The adsorption isotherms with different Li content have been calculated by Grand Canonical Monte Carlo simulations using accurate parameters for the Li−H2 interaction that were previously obtained on the basis of density functional theory calculations. We show that for the lighter +Σ〈111〉 cubic arrangement, Li doping is able to enhance the hydrogen uptake at such an extent that the U.S. Department of Energy ultimate gravimetric target is exceeded at room temperature and P=10MPa. We also find that heavy Li doping (greater than 20% of carbon atoms) becomes detrimental in terms of gravimetric adsorption performances because the H2 uptake increase is overcompensated by the heaviness of the absorbing medium. The system volumetric capacity improvement is not as good as the gravimetric and is still not sufficient to fulfill the needs of onboard hydrogen storage for light-duty fuel cell vehicles in the thermodynamic and Li content ranges explored.