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Abstract
Based on density functional theory calculation, we screened suitable Ti-decorated carbon-based hydrogen adsorbent structures. The adsorption characteristics and adsorption mechanism of hydrogen molecules on the adsorbent were also discussed. The results indicated that Ti-decorated double vacancy (2 × 2) graphene cells seem to be an efficient material for hydrogen storage. Ti atoms are stably embedded on the double vacancy sites above and below the graphene plane, with binding energy higher than the cohesive energy of Ti. For both sides of Ti-decorated double vacancy graphene, up to six H2 molecules can be adsorbed around each Ti atom when the adsorption energy per molecule is −0.25 eV/H2, and the gravimetric hydrogen storage capacity is 6.67 wt.%. Partial density of states (PDOS) analysis showed that orbital hybridization occurs between the d orbital of the adsorbed Ti atom and p orbital of C atom in the graphene layer, while the bonding process is not obvious during hydrogen adsorption. We expect that Ti-decorated double vacancy graphene can be considered as a potential hydrogen storage medium under ambient conditions.
Highlights
As an excellent substitute for fossil fuels, hydrogen is considered one of the most promising “green” fuels, because of its high heat value (144 MJ/kg), high energy density, abundant reserves, and the fact that it is environmental pollution free [1]
For Ti-decorated DV graphene, when two, four and six H2 molecules are adsorbed on both sides of the substrate, the adsorption energies per molecule are −0.31, −0.28 and −0.25 eV/H2, respectively, and these are suitable for reversible hydrogen storage media
Among the adsorbents we analyzed, the Ti-decorated double vacancy (2 × 2) cell of graphene showed the best performance as an adsorbent, with a binding energy large enough to overcome the cohesive energy of Ti, avoiding the clustering of Ti atom on graphene surface
Summary
As an excellent substitute for fossil fuels, hydrogen is considered one of the most promising “green” fuels, because of its high heat value (144 MJ/kg), high energy density, abundant reserves, and the fact that it is environmental pollution free [1]. Hydrogen storage performance is relatively poor; due to the low weight and volume densities of hydrogen adsorbed at ambient temperature, it cannot meet the strict parameters set by US Department of Energy (DOE). Traditional hydrogen storage methods use low-temperature and high-pressure liquid phase storage technology, which is difficult to apply at large scales due to high cost and safety problems [4]. Hydrogen storage in solid materials is considered to be a promising method that is safe, economical, and easy to transport. Common solid hydrogen storage materials can be divided into several categories: physical hydrogen storage such as metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), carbon-based materials, chemical hydrogen storage materials like metal hydrides, and chemical hydrides
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