Metallized HOT-graphene: A novel reversible hydrogen storage medium with ultrahigh capacity

Abstract

By performing first-principles calculations, we have researched the hydrogen storage capability of the alkali metals (Li, Na, K) and alkali-earth metal (Ca) decorated HOT graphene, a novel excellent Dirac semimetal which consists of hexagon, octagon and tetragon carbon rings. Metal Li, Na, K and Ca can be strongly bonded on HOT graphene with very large binding energy instead of forming clusters. Each metal can absorb maximum of 3, 5, 5 and 6 H2, respectively, and the average adsorption energy are all in the reversible hydrogen storage range. In the case of double-sided adsorption, 16 metals can be loaded on 2 × 2 × 1 supercell of HOT graphene and then come into being gravimetric H2 uptake of 12.34 wt%, 14.59 wt%, 11.83 wt% and 13.71 wt% for Li, Na, K and Ca decorated HOT graphene, separately, which significantly exceeds the DoE standard (6.5 wt%). The analysis of the calculated electronic density of states and charge transfer indicates that the strong bonding between metal atoms and HOT graphene is derived from orbital interaction concerning charge transfer, while the adsorption of hydrogen molecule attributes to the polarization of hydrogen molecule near ionized metal atoms and thus electrostatic and van der Waals interactions render H2 to adsorb in the metal atoms. Finally, the integrity of metal decorated HOT graphene based on ab-initio molecular dynamics (AIMD) calculation at corresponding H2 desorption temperatures indicates that the feasibility of practical application of metallized HOT-graphene system as reversible hydrogen storage medium with ultrahigh capacity. And these findings could be expected to facilitate experimental studies.