Theoretical Study on N Doping in Carbon Materials for Hydrogen Storage

Abstract

Interaction between nitrogen-substituted graphene-like compounds and hydrogen was investigated using ab initio molecular orbital method in the aspect of hydrogen storage. We adopted coronene as a model compound for fragmented graphene-like carbon materials and compared the interaction between hydrogen and pure or N-substituted coronenes by changing nitrogen positions. Among the assumed 19 N-substituted models, polarozabilities and HOMO–LUMO gaps were compared to evaluate physisorption and chemisorption energies. As for chemisorption, two N-substituted models were selected and closely examined to reveal the dependence on both nitrogen-substitution and hydrogen-adsorption positions. Potential energy surfaces as a function of H–H bond length and H₂–coronen distance showed that the barrier height for hydrogen chemisorption strongly depends on N-substitution positions. The chemisorbed products of N-substituted coronenes are stabilized or destabilized compared with the pure carbon case depending on the sites of N-substitution and H-adsorption. These results suggest that N-substitution at certain positions possibly improve hydrogen storage properties of graphene-like materials.