Ab initio simulations of H2 in Li-doped carbon nanotube systems

TL;DR

This study uses ab initio simulations to evaluate hydrogen storage in Li-doped carbon nanotubes, finding limited storage capacity and questioning the effectiveness of doping and processing for enhanced hydrogen uptake.

Contribution

It provides the first theoretical analysis of hydrogen storage in Li-doped nanotubes, showing no significant enhancement from doping or defects.

Findings

No evidence of enhanced hydrogen storage in Li-doped systems

Hydrogen uptake remains below 3.5 wt% even with defects

Diffusion barriers are high, limiting hydrogen entry into nanotubes

Abstract

Because of their unique structure, it has been proposed that carbon nanotube ropes may well provide an ideal container for the storage of molecular hydrogen. Indeed, there has been some experimental evidence of enhanced hydrogen uptake in doped Li and other alkali metal systems [Chen et al, Science 285, 91 (1999)]. We have therefore addressed this issue of hydrogen storage in Li-doped graphite and carbon nanotube systems theoretically with ab initio simulations. Our results find no evidence for such enhanced storage, based on the induced structural changes. In addition, we have also investigated the diffusion barriers for hydrogen to enter into nanotube interiors, both in the presence and absence of topological defects. Even if nanotube interiors are made accessible, the hydrogen uptake remains modest, i.e., less than 3.5 wt%. Mechanically or chemically processing nanotubes is therefore not likely to lead to greatly increased hydrogen storage.