Combining the first-principles calculations with kinetic Monte Carlo simulations of LaNi5-graphene heterojunctions as hydrogen storage materials

The hydrogen can be stored in LaNi5 via chemisorption while in graphene via physisorption. The heterojunctions were designed using the LaNi5(100) surface and graphene with layer distances of 4–8 Å as hydrogen storage materials. Ab initio molecular dynamics simulations were performed to examine the heterojunctions’ stability. The first-principles calculations showed that the hydrogen atom can stably adsorb on 6 m sites (a tetrahedral interstitial structure) on LaNi5(100) surface. The hydrogen migration kinetics were investigated by combining the CI-NEB method and kinetic Monte Carlo simulations. The H migration barriers between adjacent 6 m sites on LaNi5 layer surface are decreased for all LaNi5-graphene (LG) structures. Subsequently, along the maximum energy path 6ma - 4ha - 12nb inside LaNi5 layer of LG, significant decreases are observed in both migration barriers and optimal reaction temperatures. The migration barrier in pure LaNi5(100) is 1.432 eV with the reaction temperature of 532 K. For LG_4 Å and LG_5 Å, the migration barriers are reduced to 1.160 and 1.210 eV, respectively, corresponding with the reaction temperatures of 436 and 454 K. The hydrogen storage density of LG is around 2.10 wt%. LaNi5-graphene heterojunctions showed good hydrogen kinetics and storage density, indicating promising potential as hydrogen storage materials. [Display omitted] •The LaNi5-graphene heterojunctions were constructed for hydrogen storage.•Hydrogen migration barriers between different adsorption sites in LaNi5were calculated.•The migration kinetics of hydrogen are enhanced in the LaNi5-graphene heterojunctions.•The hydrogen storage density of LaNi5-graphene is improved to 2.10 wt%.