PNNL

Abstract

Carbon sorbent materials have shown great promise for solid-state hydrogen storage. The modification of these materials with nitrogen (N) dopants has been undertaken to develop materials that can store hydrogen at ambient temperatures. In this work density functional theory (DFT) calculations are used to systematically probe the influence of curvature on the stability and activity of non-doped and N-doped carbon materials towards hydrogen binding. Specifically, we use four models of carbon materials: graphene, [5,5] carbon nanotube, [5,5] D5d-C120 and C60, to extract and correlate the thermodynamic properties of active sites with varying degrees of sp2 hybridization (curvature). From our calculations and analysis, we find that graphitic N-doping is thermodynamically favored on more pyramidal sites with increased curvature. In contrast, we find that the hydrogen binding energy is weakly affected by curvature and is dominated by electronic effects induced by N-doping. These findings highlight the importance of modulating the heteroatom doping configuration and the lattice topology when developing materials for H2 storage.