On hydrogen storage in metal-decorated trans-polyacetylene

Abstract 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 TiH 3 or ScH 2 , one structural unit of TiH 3 (ScH 2 ) 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 (C 4 H 2 ·2TiH 3 ) n ((C 4 H 2 ·2ScH 2 ) n ), where two out of four hydrogen atoms in the C 4 H 4 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.