On hydrogen storage in metal-decorated trans-polyacetylene

We propose metal-decorated trans-polyacetylene as a hydrogen storage medium using first-principles calculations based on the density-functional theory. When a hydrogen atom in polyacetylene is replaced by a TiH3 or ScH2, one structural unit of TiH3 (ScH2) can maximally bind five (six) hydrogen molecules with the binding energy of about 0.20 eV/H-2. The molecular formula of the optimal structure is (C4H2 center dot 2TiH(3))(n) ((C4H2 center dot 2ScH(2))(n)), where two out of four hydrogen atoms in the C4H4 Unit in polyacetylene are substituted by 2TiH(3) (2ScH(2)) units. Theoretically, the gravimetric and volumetric densities of the maximally stored hydrogen molecules here are 12 (14) wt.% and 140 kg/m(3), respectively. (C) 2007 Elsevier B.V. All rights reserved.