  The capacity of Ti-capped sp carbon atomic chains for use as hydrogen storage
media is studied using first-principles density functional theory. The Ti atom
is strongly attached at one end of the carbon chains via d-p hybridization,
forming stable TiCn complexes. We demonstrate that the number of adsorbed H2 on
Ti through Kubas interaction depends upon the chain types. For polyyne (n even)
or cumulene (n odd) structures, each Ti atom can hold up to five or six H2
molecules, respectively. Furthermore, the TiC5 chain effectively terminated on
a C20 fullerene can store hydrogen with optimal binding of 0.52 eV/H2. Our
results reveal a possible way to explore high-capacity hydrogen storage
materials in truly one-dimensional carbon structures.
