Leveraging Curvature on N-Doped Carbon Materials for Hydrogen Storage

Carbon sorbent materials have shown great promise for solid-state hydrogen (H₂) storage. Modification of these materials with nitrogen (N) dopants has been undertaken to develop materials that can store H₂ 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 undoped and N-doped carbon materials toward H binding. Specifically, four models of carbon materials are used: graphene, [5,5] carbon nanotube, [5,5] D_5d-C_120, and C₆₀, to extract and correlate the thermodynamic properties of active sites with varying degrees of sp² hybridization (curvature). From the calculations and analysis, it is found that graphitic N-doping is thermodynamically favored on more pyramidal sites with increased curvature. In contrast, it is found 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.