Hydrogen Storage Capacity Study of a Li+Graphene Composite System with Different Charge States

Based on first-principles plane-wave calculations,we firstly reconfirm that the Li+graphene complex can be taken as a hydrogen storage medium with capacity of 12.8wt%.Then metal adsorption properties of this Li+graphene system with different charge states are investigated.Finally,the hydrogen storage ability of the charging system is calculated.Our calculations show that adding positive charge on a Li+graphene composite results in a conspicuous reduction of Li2s and Li2p orbital occupation with respect to the C2p state.As a result,a stronger bonding between Li and graphene is formed,and a special double-layer hydrogen adsorption structure has been found.Compared to the neutral system,utilizing the positive charged Li+graphene to store hydrogen molecules can solve the issue of clustering of metal atoms after releasing hydrogen,and can improve hydrogen storage capacity up to a gravimetric density of 20.4wt%,correspondingly one adsorbed Li atom can effectively absorb up to seven H2 molecules.